Earnings Per Share [Abstract] Schedule of Earnings Per Share Reconciliation Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Revenue from Contract with Customer [Abstract] Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Commitments and Contingencies Disclosure [Abstract] Long-term Purchase Commitment [Table] Long-term Purchase Commitment [Table] Jointly Owned Utility Plant [Axis] Jointly Owned Utility Plant [Axis] Jointly Owned Utility Plant [Domain] Jointly Owned Utility Plant [Domain] Busch Ranch I Wind Farm Busch Ranch I Wind Farm [Member] Busch Ranch I Wind Farm [Member] Segments [Axis] Segments [Axis] Segment [Domain] Segments [Domain] Electric Utilities Electric Utilities [Member] Electric Utilities Segment [Member] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] AltaGas AltaGas [Member] AltaGas Long-term Purchase Commitment [Line Items] Long-term Purchase Commitment [Line Items] Utility Plant, Megawatt Capacity Utility Plant, Megawatt Capacity Utility Plant, Megawatt Capacity Jointly Owned Utility Plant, Proportionate Ownership Share Jointly Owned Utility Plant, Proportionate Ownership Share Business Acquisition, Percentage of Voting Interests Acquired Business Acquisition, Percentage of Voting Interests Acquired Business Combination, Consideration Transferred Business Combination, Consideration Transferred Discontinued Operations and Disposal Groups [Abstract] Disposal Groups, Including Discontinued Operations, Balance Sheet Accounts Disposal Groups, Including Discontinued Operations, Balance Sheet Accounts [Table Text Block] Disposal Groups, Including Discontinued Operations, Balance Sheet Accounts [Table Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Segment Reporting Segment Reporting, Policy [Policy Text Block] Use of Estimates and Basis of Presentation Use of Estimates, Policy [Policy Text Block] Cash and Cash Equivalents and Restricted Cash Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Investments Investment, Policy [Policy Text Block] Recently Issued and Adopted Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Revenue Recognition Revenue Recognition, Policy [Policy Text Block] Fair Value Disclosures [Abstract] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Carrying Amount Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents, Fair Value Cash and Cash Equivalents, Fair Value Disclosure Restricted cash Restricted Cash and Investments, Current Restricted Cash Fair Value Disclosure Restricted Cash Fair Value Disclosure This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This element represents the fair value of assets categorized as restricted cash Notes payable Short-term Debt Notes payable, Fair Value Short-term Debt, Fair Value Long-term debt, including current maturities Long-term Debt Long-term debt, including current maturities, Fair Value Long-term Debt, Fair Value Statement [Table] Statement [Table] Regulatory Liability [Axis] Regulatory Liability [Axis] Regulatory Liability [Domain] Regulatory Liability [Domain] TCJA Revenue Reserve Subject to Refund Revenue Subject to Refund [Member] Statement [Line Items] Statement [Line Items] Number of States That Have Received State Utility Commission Approvals to Provide the Benefits of Federal Tax Reform to Utility Customers Number of States That Have Received State Utility Commission Approvals to Provide the Benefits of Federal Tax Reform to Utility Customers Number of States That Have Received State Utility Commission Approvals to Provide the Benefits of Federal Tax Reform to Utility Customers Estimated and recorded revenue reduction from TCJA tax benefits Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Regulatory Liabilities Regulatory Liabilities Revenue refunded to customers as a result of the TCJA tax benefits Revenue Refunded To Customers As A Result Of The TCJA Tax Benefits Revenue Refunded To Customers As A Result Of The TCJA Tax Benefits Statement of Comprehensive Income [Abstract] Other Comprehensive Income (Loss) Comprehensive Income (Loss) Note [Text Block] Supplemental Cash Flow Information [Abstract] Supplemental Disclosure of Cash Flow Information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Business Group [Axis] Business Group [Axis] Business Group (grouping of segments) [Axis] Business Group [Domain] Business Group [Domain] [Domain] for Business Group (grouping of segments) [Axis] Utilities Group Utilities Group [Member] Utilities Group - consists of our Electric Utilities and our Gas Utilities segments Related Party Transaction [Line Items] Related Party Transaction [Line Items] Restricted Net Assets for Subsidiaries Restricted Net Assets for Subsidiaries Amount of Restricted Net Assets (Equity) for Subsidiaries as of the end of the reporting period. Non-cash Investing and Financing Activities from Continuing Operations [Abstract] Noncash Investing and Financing Items [Abstract] Property, plant and equipment acquired with accrued liabilities Capital Expenditures Incurred but Not yet Paid Increase (decrease) in capitalized assets associated with asset retirement obligations Increase (Decrease) in Asset Retirement Obligations Supplemental Cash Flow Elements [Abstract] Supplemental Cash Flow Elements [Abstract] Interest (net of amounts capitalized) Interest Paid, Net Income taxes (paid) refunded Income Taxes Paid, Net Reclassification Out Of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification Out Of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification Out Of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Member] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] Accumulated Defined Benefit Plans Adjustment Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Interest Rate Contract Interest Rate Contract [Member] Commodity Contract Commodity Contract [Member] Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Interest expense Interest Costs Incurred Net (loss) from discontinued operations Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax Fuel, purchased power and cost of natural gas sold Fuel, Purchased Power and Cost of Gas Sold Fuel costs incurred that are directly related to goods produced and sold and services rendered during the reporting period, combined with the amount of purchased power charged against earnings for the period, and cost of gas sold to customers for the period. Operations and maintenance Operating Expense, Maintenance, Operations, and Other Costs and Expense Amount of operating expenses for the period including selling, general, and administrative expenses, costs include routine repairs and maintenance and operations. Income (loss) before earnings (loss) of unconsolidated subsidiaries and income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Income tax benefit (expense) Income Tax Expense (Benefit) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Regulatory Assets and Liabilities Disclosure [Abstract] Schedule of Regulatory Assets and Liabilities Schedule of Regulatory Assets and Liabilities [Table Text Block] The entire disclosure for detailed information about regulatory assets and liabilities, including current and noncurrent assets created when regulatory agencies permit the deferral of costs to the balance sheet that would otherwise be required to appear on the company's income statement and would be charged against current expenses or revenues, as well as current and noncurrent liabilities created when regulatory agencies permit. [Table Text Block] Schedule of TCJA (Federal Tax Reform) Benefits Passed On To Customers By State Schedule of TCJA (Federal Tax Reform) Benefits Passed On To Customers By State [Table Text Block] [Table Text Block] for Schedule of TCJA (Federal Tax Reform) Benefits Passed On To Customers By State [Table] Statement of Stockholders' Equity [Abstract] Total Stockholders’ Equity Parent [Member] Noncontrolling Interest Noncontrolling Interest [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Total Equity, beginning balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Net income (loss) Net Income (Loss) Including Portion Attributable to Noncontrolling Interest (Excluding Income Loss Attributable to Redeemable Noncontrolling Interest) Net Income (Loss) Including Portion Attributable to Noncontrolling Interest (Excluding Income Loss Attributable to Redeemable Noncontrolling Interest) Other comprehensive income Other Comprehensive Income (Loss), Net of Tax Dividends on common stock Dividends, Common Stock, Cash Share-based compensation Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Dividend reinvestment and stock purchase plan Stock Issued During Period, Value, Dividend Reinvestment Plan Redeemable noncontrolling interest Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests Cumulative effect of ASU 2016-09 implementation Adjustment to Additional Paid in Capital, Income Tax Effect from Share-based Compensation, Net Other stock transactions Stockholders' Equity, Other Distribution to noncontrolling interest Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Total Equity, ending balance Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Discontinued Operations, Held-for-sale or Disposed of by Sale Discontinued Operations, Held-for-sale or Disposed of by Sale [Member] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Disposal Group, Including Discontinued Operations, Impairment Of Long-lived Assets (Net of Tax) Disposal Group, Including Discontinued Operations, Impairment Of Long-lived Assets (Net of Tax) Disposal Group, Including Discontinued Operations, Impairment Of Long-lived Assets (Net of Tax) Inventory, Net [Abstract] Materials, Supplies and Fuel Inventory Disclosure [Text Block] Segment Reporting Information, Additional Information [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] External Operating Revenue External Customers [Member] External Customers Inter-company Operating Revenue Intercompany Customers [Member] Intercompany Customers [Member] Gas Utilities Gas Utilities [Member] Gas Utilities [Member] Power Generation Power Generation [Member] Power Generation Mining Mining [Member] Mining Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Inter-company Revenues Intersegment Eliminations [Member] Corporate Corporate, Non-Segment [Member] Consolidation, Eliminations Consolidation, Eliminations [Member] Restructuring Type [Axis] Restructuring Type [Axis] Type of Restructuring [Domain] Type of Restructuring [Domain] Other Restructuring Other Restructuring [Member] Products and Services [Axis] Products and Services [Axis] Products and Services [Domain] Products and Services [Domain] Other Revenues Other [Member] Other [Member] Segment Reporting Information Segment Reporting Information [Line Items] Revenue from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax Revenues Revenues Net income (loss) from continuing operations Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Deferred income taxes Deferred Income Tax Expense (Benefit) Net income attributable to noncontrolling interests Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Net tax benefit Tax Adjustments, Settlements, and Unusual Provisions Revenue Revenue from Contract with Customer [Text Block] Management's Statement Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Risk Management Activities Derivative Instruments and Hedging Activities Disclosure [Text Block] Fair Value of Financial Instruments Fair Value Disclosures [Text Block] Contract or notional amounts and terms of marketing activities and derivative commodity instruments Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Derivative Instruments, Gain (Loss) Derivative Instruments, Gain (Loss) [Table Text Block] Document and Entity Information [Abstract] Abstract model section heading for document and entity information Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Document Type Document Type Document Period End Date Document Period End Date Amendment Flag Amendment Flag Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Current Fiscal Year End Date Current Fiscal Year End Date Entity Current Reporting Status Entity Current Reporting Status Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Statement of Cash Flows [Abstract] Operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Loss from discontinued operations, net of tax Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent Income from continuing operations Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation, depletion and amortization Depreciation, Depletion and Amortization Deferred financing cost amortization Amortization of Debt Issuance Costs and Discounts Stock compensation Share-based Compensation Employee benefit plans Pension and Other Postretirement Benefits Cost (Reversal of Cost) Other adjustments, net Other Noncash Income (Expense) Changes in certain operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Materials, supplies and fuel Increase (Decrease) in Inventories Accounts receivable, unbilled revenues and other operating assets Increase (Decrease) in Accounts Receivable and Other Operating Assets Accounts payable and other operating liabilities Increase (Decrease) in Other Accounts Payable and Accrued Liabilities Regulatory assets - current Increase (Decrease) in Other Regulatory Assets Regulatory liabilities - current Increase (Decrease) in Regulatory Liabilities Contributions to defined benefit pension plans Payment for Pension Benefits Other operating activities, net Increase (Decrease) in Other Operating Assets and Liabilities, Net Net cash provided by operating activities of continuing operations Net Cash Provided by (Used in) Operating Activities, Continuing Operations Net cash provided by (used in) operating activities of discontinued operations Cash Provided by (Used in) Operating Activities, Discontinued Operations Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Property, plant and equipment additions Payments to Acquire Property, Plant, and Equipment Purchase of investment Payments to Acquire Other Investments Other investing activities Payments for (Proceeds from) Other Investing Activities Net cash provided by (used in) investing activities of continuing operations Net Cash Provided by (Used in) Investing Activities, Continuing Operations Net cash provided by (used in) investing activities of discontinued operations Cash Provided by (Used in) Investing Activities, Discontinued Operations Net cash provided by (used in) investing activities Net Cash Provided by (Used in) Investing Activities Financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Dividends paid on common stock Payments of Dividends Common stock issued Proceeds from Issuance of Common Stock Net (payments) borrowings of short-term debt Proceeds from (Repayments of) Short-term Debt Proceeds from Issuance of Long-term Debt Proceeds from Issuance of Long-term Debt Long-term debt - repayments Repayments of Long-term Debt Distributions to noncontrolling interest Payments to Noncontrolling Interests Other financing activities Proceeds from (Payments for) Other Financing Activities Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Net change in cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect Cash, cash equivalents and restricted cash at beginning of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash, cash equivalents and restricted cash at end of period Schedule Of Regulatory Assets And Liabilities [Table] Schedule Of Regulatory Assets And Liabilities [Table] A table of assets and liabilities that are created when regulatory agencies permit public utilities to defer recognitiion of certain revenues or costs included in rate setting. Regulatory Asset [Axis] Regulatory Asset [Axis] Regulatory Asset [Domain] Regulatory Asset [Domain] Deferred energy and fuel cost adjustments - current Deferred Fuel Costs [Member] Deferred gas cost adjustments Asset Recoverable Gas Costs [Member] Gas price derivatives Price Risk Derivative [Member] Deferred taxes on AFUDC Allowance For Funds Used During Construction [Member] The offsetting entry to other income when an enterprise capitalizes, as part of the cost of plant and equipment, the cost of financing construction as financed partially by equity. Employee benefit plans Pension and Other Postretirement Plans Costs [Member] Environmental Environmental [Member] Environmental costs associated with utility property [Member] Asset retirement obligations Asset Retirement Obligation Costs [Member] Loss on reacquired debt Loss on Reacquired Debt [Member] Renewable energy standard adjustment Renewable Energy Program [Member] Deferred taxes on flow through accounting Flow Through Accounting [Member] The income tax effects of certain tax items are reflected in cost of service for the customer in which the tax benefits are realized and result in lower utiity rates. The regulatory treatment under flow-through accounting was applied for this tax benefit generated by utility costs that were previously capitalized for tax purposes in a rate case settlement and resulted in a lower rate increase. A regulatory asset was established to reflect the future increase in taxes payable recovered from sutomers as the temporarty difference reverses.[Member] Decommissioning costs Environmental Restoration Costs [Member] Gas supply contract termination Gas Supply Contract Termination [Member] Gas Supply Contract Termination [Member] Other regulatory assets Other Regulatory Assets [Member] Other regulatory assets [Member] Deferred energy and gas costs Cost of removal Removal Costs [Member] Excess deferred income taxes Deferred Income Tax Charges a [Member] Rate Action of a regulator resulting in capitalization or accrual of income taxes TCJA revenue reduction Other regulatory liabilities Other Regulatory Liabilities [Member] Other regulatory liabilities [Member] Schedule Of Regulatory Assets And Liabilities [Line Items] Schedule Of Regulatory Assets And Liabilities [Line Items] Schedule of regulatory asset and liabilities line items Regulatory assets Net Regulatory Assets [Abstract] Regulatory assets Regulatory Assets Less current regulatory assets Regulatory Assets, Current Regulatory assets, non-current Regulatory Assets, Noncurrent Regulatory liabilities Regulatory Assets and Liabilities, Other Disclosures [Abstract] Regulatory liabilities Less current regulatory liabilities Regulatory Liability, Current Regulatory liabilities, non-current Regulatory Liability, Noncurrent Fair Value of Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Designated as Hedging Instrument Designated as Hedging Instrument [Member] Not Designated as Hedging Instrument Not Designated as Hedging Instrument [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Derivative assets — current Derivative Assets, Current [Member] Line item in the statement of financial position in a classified presentation in which the fair value amounts of the derivative instruments are included. Other assets, non-current Derivative Assets, Noncurrent [Member] Line item in the statement of financial position in a classified presentation in which the fair value amounts of the derivative instruments are included. Current assets held for sale Current Assets Held For Sale [Member] Current Assets Held For Sale [Member] Derivative liabilities — current Derivative Liabilities, Current [Member] Line item in the statement of financial position in a classified presentation in which the fair value amounts of the derivative instruments are included. Current liabilities held for sale Current Liabilities Held For Sale [Member] Current Liabilities Held For Sale [Member] Other deferred credits and other liabilities Derivative Liabilities, Noncurrent [Member] Line item in the statement of financial position in a classified presentation in which the fair value amounts of the derivative instruments are included. Noncurrent liabilities held for sale Noncurrent Liabilities Held For Sale [Member] Noncurrent Liabilities Held For Sale [Member] Derivatives, Carrying Amount and Fair Value [Line Items] Derivatives, Fair Value [Line Items] Derivative Asset, Fair Value, Gross Asset Derivative Asset, Fair Value, Gross Asset Derivative Asset, Fair Value, Gross Liability Derivative Asset, Fair Value, Gross Liability Derivative Liability, Fair Value, Gross Asset Derivative Liability, Fair Value, Gross Asset Derivative Liability, Fair Value, Gross Liability Derivative Liability, Fair Value, Gross Liability Derivative Asset, Fair Value, Net Derivative Asset, Fair Value, Amount Not Offset Against Collateral Derivative Liability, Fair Value, Net Derivative Liability, Fair Value, Amount Not Offset Against Collateral Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Equity compensation Stock Compensation Plan [Member] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Anti-dilutive shares Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Corporate Term Loan Due 2033 Corporate Term Loan Due 2033 [Member] Corporate Term Loan Due 2033 Remarketable Junior Subordinated Notes Due 2028 Remarketable Junior Subordinated Notes Due 2028 [Member] Remarketable Junior Subordinated Notes Due 2028 [Member] Corporate Term Loan Due July 2020 Corporate Term Loan Due July 2020 [Member] Corporate Term Loan Due July 2020 [Member] Extinguishment of Debt [Axis] Extinguishment of Debt [Axis] Extinguishment of Debt, Type [Domain] Extinguishment of Debt, Type [Domain] Junior Subordinated Debt Junior Subordinated Debt [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] Base Rate Base Rate [Member] Eurodollar Eurodollar [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Proceeds from Issuance of Senior Long-term Debt Proceeds from Issuance of Senior Long-term Debt Debt Instrument, Interest Rate, Stated Percentage Debt Instrument, Interest Rate, Stated Percentage Extinguishment of Debt, Amount Extinguishment of Debt, Amount Long-term Debt, Gross Long-term Debt, Gross Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Long-term Contract for Purchase of Electric Power [Axis] Long-term Contract for Purchase of Electric Power [Axis] Long-term Contract for Purchase of Electric Power [Domain] Long-term Contract for Purchase of Electric Power [Domain] Sale Agreement Between Colorado IPP and Affiliate Colorado Electric Sale Agreement Between Colorado IPP and Affiliate Colorado Electric [Member] Sale Agreement Between Colorado IPP and Affiliate Colorado Electric [Member] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Long-term Purchase Commitment, Period Long-term Purchase Commitment, Period Discontinued Operations Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Interest rate swaps Interest Rate Swap [Member] Reclassification adjustment of benefit plan - prior service cost, (tax) benefit Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, Tax Reclassification adjustment of benefit plan liabilities, (tax) benefit Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax Net unrealized gains/losses, (tax) benefit Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax Reclassification of net realized gains/losses, (tax) benefit Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax Fair Value Measurements Derivatives and Fair Value [Text Block] Net income available for common stock Net Income (Loss) Available to Common Stockholders, Basic Weighted average shares - basic (in shares) Weighted Average Number of Shares Outstanding, Basic Dilutive effect of: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Equity Units (in shares) Incremental Common Shares Attributable to Dilutive Effect of Equity Unit Purchase Agreements Equity compensation (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Weighted average shares - diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Subsequent Events [Abstract] Subsequent Events Subsequent Events [Text Block] Income Tax Disclosure [Abstract] Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Long-term Investments [Abstract] Investments Investment [Table Text Block] Derivative [Table] Derivative [Table] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Interest Expense Interest Expense [Member] Net (loss) from Discontinued Operations Net (loss) from Discontinued Operations [Member] Net (loss) from Discontinued Operations [Member] Cost of Sales Cost of Sales [Member] Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Cash Flow Hedging Cash Flow Hedging [Member] Derivative [Line Items] Derivative [Line Items] Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net Derivative, Gain (Loss) on Derivative, Net Derivative, Gain (Loss) on Derivative, Net Defined Benefit Plan [Abstract] Employee Benefit Plans Pension and Other Postretirement Benefits Disclosure [Text Block] Statement of Financial Position [Abstract] Common Stock, Par Value (usd per share) Common Stock, Par or Stated Value Per Share Common Stock, Shares Issued Common Stock, Shares, Issued Treasury Stock, Shares Treasury Stock, Shares Common Stock, Shares Authorized Common Stock, Shares Authorized Sales Revenue, Net Sales Revenue, Net [Member] Price Risk Derivative Regulatory assets Schedule of Net Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Schedule of Defined Benefit Plans Contributions Schedule of Defined Benefit Plans Contributions [Table Text Block] Schedule of Defined Benefit Plans Contributions for the current year and specific future years.[Text Block] Regulatory Agency [Axis] Regulatory Agency [Axis] Regulatory Agency [Domain] Regulatory Agency [Domain] Arkansas Public Service Commission (APSC) Arkansas Public Service Commission (APSC) [Member] Arkansas Public Service Commission (APSC) Colorado Public Utilities Commission (CPUC) Colorado Public Utilities Commission (CPUC) [Member] Colorado Public Utilities Commission (CPUC) [Member] Iowa Utilities Board (IUB) Iowa Utilities Board (IUB) [Member] Iowa Utilities Board (IUB) [Member] Kansas Public Utilities Commission (KPUC) Kansas Public Utilities Commission (KPUC) [Member] Kansas Public Utilities Commission (KPUC) [Member] Nebraska Public Service Commission (NPSC) Nebraska Public Service Commission (NPSC) [Member] Nebraska Public Service Commission (NPSC) [Member] South Dakota Public Utilities Commission (SDPUC) South Dakota Public Utilities Commission (SDPUC) [Member] South Dakota Public Utilities Commission (SDPUC) [Member] Schedule of Short-term Debt [Table] Schedule of Short-term Debt [Table] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Revolving Credit Facility Revolving Credit Facility [Member] Short-term Debt, Type [Axis] Short-term Debt, Type [Axis] Short-term Debt, Type [Domain] Short-term Debt, Type [Domain] Commercial Paper Commercial Paper [Member] Letter of Credit Letter of Credit [Member] Short-term Debt [Line Items] Short-term Debt [Line Items] Letters of Credit Letters of Credit Outstanding, Amount Current borrowing capacity Line of Credit Facility, Current Borrowing Capacity Number of extension options Number Of One-Year Extension Options Number Of One-Year Extension Options; related to a revolving credit facility. Debt term Debt Instrument, Term Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Interest rate Line of Credit Facility, Interest Rate at Period End Commitment fee Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Commercial paper, maximum borrowing capacity Commercial Paper, Maximum Borrowing Capacity Commercial Paper, Maximum Borrowing Capacity Short-term interest rate Short-term Debt, Weighted Average Interest Rate, at Point in Time Senior Unsecured Notes Due 2019 Senior Unsecured Notes Due 2019 [Member] Senior Unsecured Notes Due 2019 Corporate Term Loan Due June 2021 Corporate Term Loan Due June 2021 [Member] Corporate Term Loan Due June 2021 [Member] Current maturities of long-term debt Long-term Debt, Current Maturities Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Defined Benefit Pension Plans Pension Plan [Member] Defined Benefit Postretirement Healthcare Plans Other Postretirement Benefits Plan [Member] Supplemental Non-qualified Defined Benefit and Defined Contribution Plans Supplemental Employee Retirement Plan [Member] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Prior service cost (benefit) Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Net loss (gain) Defined Benefit Plan, Amortization of Gain (Loss) Net periodic benefit cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Payment for Pension and Other Postretirement Benefits [Abstract] Payment for Pension and Other Postretirement Benefits [Abstract] Contributions made to the Defined Benefit Pension Plan Payment for Pension and Other Postretirement Benefits Contributions by Employer Defined Benefit Plan, Plan Assets, Contributions by Employer Estimated Future Employer Contributions in Current Fiscal Year Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year Estimated Future Employer Contributions in Next Fiscal Year Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value, Measurements, Recurring Fair Value, Measurements, Recurring [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Fair Value, Inputs, Level 1 Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 2 Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 3 Fair Value, Inputs, Level 3 [Member] Estimate of Fair Value Measurement Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Derivative Assets, Commodity Derivatives Derivative Asset Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset Derivative Assets, Total Assets, Fair Value Disclosure Derivative Liabilities, Fair Value Disclosure Derivative Liability Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset Derivative Liabilities, Total Financial and Nonfinancial Liabilities, Fair Value Disclosure Segment Reporting Schedule of Segment Reporting Information, by Segment [Table Text Block] Reconciliation of Assets from Segment to Consolidated Reconciliation of Assets from Segment to Consolidated [Table Text Block] Materials and supplies Inventory, Raw Materials and Supplies, Gross Fuel - Electric Utilities Energy Related Inventory, Other Fossil Fuel Natural gas in storage held for distribution Energy Related Inventory, Natural Gas in Storage Total materials, supplies and fuel Inventory, Net Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2014-09 Accounting Standards Update 2014-09 [Member] Amount of cumulative adoption adjustment to the opening balance of Retained Earnings Cumulative Effect of New Accounting Principle in Period of Adoption Payables and Accruals [Abstract] Accrued employee compensation, benefits and withholdings Employee-related Liabilities, Current Accrued property taxes Accrual for Taxes Other than Income Taxes, Current Customer deposits and prepayments Customer Advances and Deposits, Current Accrued interest and contract adjustment payments Interest Payable, Current CIAC current portion Customer Advances for Construction Other (none of which is individually significant) Other Accrued Liabilities, Current Total accrued liabilities Accrued Liabilities, Current Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract] Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract] Disposal Group, Including Discontinued Operation, (Gain) Loss On Sale Of Assets Disposal Group, Including Discontinued Operation, (Gain) Loss On Sale Of Assets Disposal Group, Including Discontinued Operation, (Gain) Loss On Sale Of Assets Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract] Other current assets Disposal Group, Including Discontinued Operation, Other Assets, Current Derivative assets, current and noncurrent Disposal Group, Including Discontinued Operation, Derivative Assets (Current and Noncurrent) Disposal Group, Including Discontinued Operation, Derivative Assets (Current and Noncurrent) Deferred income tax assets, noncurrent, net Disposal Group, Including Discontinued Operation, Deferred Tax Assets, Noncurrent Property, plant and equipment, net Disposal Group, Including Discontinued Operation, Property, Plant and Equipment Other current liabilities Disposal Group, Including Discontinued Operation, Other Liabilities Derivative liabilities, current and noncurrent Disposal Group, Including Discontinued Operations, Derivative Liabilities (Current and Noncurrent) Disposal Group, Including Discontinued Operations, Derivative Liabilities (Current and Noncurrent) Deferred income tax liabilities, noncurrent, net Disposal Group, Including Discontinued Operation, Deferred Tax Liabilities, Noncurrent Other noncurrent liabilities Disposal Group, Including Discontinued Operation, Other Liabilities, Noncurrent Net assets Disposal Group, Including Discontinued Operation, Assets Notes Payable, Current Maturities and Debt Debt Disclosure [Text Block] Effective Income Tax Rate Reconciliation, Percent [Abstract] Effective Income Tax Rate Reconciliation, Percent [Abstract] Federal statutory rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent State income tax (net of federal tax effect) Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent Percentage depletion in excess of cost Effective Income Tax Rate Reconciliation, Nondeductible Expense, Depletion, Percent Accounting for uncertain tax positions adjustment Effective Income Tax Rate Reconciliation, Tax Contingency, Percent Noncontrolling interest Effective Income Tax Rate Reconciliation, Noncontrolling Interest Income (Loss), Percent IRC 172(f) carryback claim Effective Income Tax Rate Reconciliation, NOL Carryback Specified Liability Loss Effective Income Tax Rate Reconciliation, NOL Carryback Specified Liability Loss Tax credits Effective Income Tax Rate Reconciliation, Tax Credit, Percent Effective tax rate adjustment Effective Income Tax Rate Reconciliation, Inter-period Tax Allocation, Percent Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to an inter-period tax allocation. Flow-through adjustments Effective Income Tax Rate Reconciliation, Flow Through Accounting The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by Flow Through Accounting. TCJA change in estimate Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent AFUDC equity Effective Income Tax Rate Reconciliation Allowance For Other Funds Used During Construction, Equity The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by the equity portion of allowance for other funds used during construction, a nondeductible expense. Jurisdictional simplification project Effective Income Tax Reconciliation, Tax Benefit Related to Legal Restructuring Effective Income Tax Reconciliation, Tax Benefit Related to Legal Restructuring. Other tax differences Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Effective Tax Rate Effective Income Tax Rate Reconciliation, Percent Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount Investment [Table] Investment [Table] Asset Class [Axis] Asset Class [Axis] Asset Class [Domain] Asset Class [Domain] Cost method investment Cost-method Investments [Member] Cash surrender value of life insurance contracts Cash Surrender Value [Member] Investment [Line Items] Investment [Line Items] Assets held for sale contributed in exchange for equity securities in a privately held company Assets Held for Sale Used to Acquire Other Investments Assets Held for Sale Used to Acquire Other Investments Total investments Long-term Investments At The Market Equity Offering Program Authorized Aggregate Value At The Market Equity Offering Program Authorized Aggregate Value At The Market Equity Offering Program authorized an aggregate value that the Company may, through its sales agents, offer and sell from time to time shares of its common stock. Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Debt Instrument, Convertible, Consecutive Trading Days for Calculation of Applicable Market Value Debt Instrument, Convertible, Consecutive Trading Days for Calculation of Applicable Market Value Debt Instrument, Convertible, Consecutive Trading Days for Calculation of Applicable Market Value Debt Instrument, Convertible, If Applicable Market Value Greater Than Reference Price, Amount Used To Calculate Number of Shares, Numerator Debt Instrument, Convertible, If Applicable Market Value Greater Than Reference Price, Amount Used To Calculate Number of Shares, Numerator Debt Instrument, Convertible, If Applicable Market Value Greater Than Reference Price, Amount Used To Calculate Number of Shares, Numerator Debt Instrument, Convertible, Conversion Ratio Debt Instrument, Convertible, Conversion Ratio Sale of Stock, Consideration Received on Transaction Sale of Stock, Consideration Received on Transaction Sale of Stock, Number of Shares Issued in Transaction Sale of Stock, Number of Shares Issued in Transaction Schedule of Accrued Liabilities Schedule of Accrued Liabilities [Table Text Block] Reclassification Out of Accumulated Other Comprehensive Income (Loss) Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] Schedule of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Receivables [Abstract] Accounts Receivable Loans, Notes, Trade and Other Receivables Disclosure [Text Block] Business Segment Information Segment Reporting Disclosure [Text Block] Materials, Supplies and Fuel Schedule of Inventory, Current [Table Text Block] Schedule of Short-term Debt Schedule of Short-term Debt [Table Text Block] Schedule of Credit Facility Covenants Credit Facility and Short Term Debt Covenants [Table Text Block] Schedule of significant debt covenants related to Credit Facility and other short-term debt [Table Text Block] Energy [Axis] Energy [Axis] Energy [Domain] Energy [Domain] Natural Gas, Distribution Natural Gas, Distribution [Member] Natural Gas for distribution [Member] Future Future [Member] Commodity Option Commodity Option [Member] Basis Swap Basis Swap [Member] Fixed for Float Swaps Purchased Fixed for Float Swaps Purchased [Member] Fixed for Float Swaps Purchased [Member] Natural Gas Physical Purchases Natural Gas Physical Purchases [Member] Natural Gas Physical Purchases [Member] Derivative, Nonmonetary Notional Amount Derivative, Nonmonetary Notional Amount Derivative, Remaining Maturity Derivative, Remaining Maturity Derivative, Nonmonetary Notional Amount, Energy Measure Derivative, Nonmonetary Notional Amount, Energy Measure Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months Credit Risk Derivative Liabilities, at Fair Value Collateral Already Posted, Aggregate Fair Value Equity Stockholders' Equity Note Disclosure [Text Block] Derivative Expired During the Period Derivative Expired During the Period Derivative Expired During the Period Retail Retail [Member] Retail [Member] Transportation Transportation [Member] Transportation [Member] Wholesale Wholesale [Member] Wholesale [Member] Market - off-system sales Market Off-System Sales [Member] Market Off-System Sales [Member] Transmission/Other Transmission/Other [Member] Transmission/Other [Member] Other revenues Timing of Transfer of Good or Service [Axis] Timing of Transfer of Good or Service [Axis] Timing of Transfer of Good or Service [Domain] Timing of Transfer of Good or Service [Domain] Services transferred at a point in time Transferred at Point in Time [Member] Services transferred over time Transferred over Time [Member] Total revenues Supplemental Disclosure of Cash Flow Information Cash Flow, Supplemental Disclosures [Text Block] Investments Investment [Text Block] Reconciliation of Assets from Segment to Consolidated [Table] Reconciliation of Assets from Segment to Consolidated [Table] Discontinued Operations, Held-for-sale Discontinued Operations, Held-for-sale [Member] Segment Reporting, Asset Reconciling Item [Line Items] Segment Reporting, Asset Reconciling Item [Line Items] Assets Assets Other comprehensive income (loss), net of tax: Other Comprehensive Income (Loss), Net of Tax [Abstract] Reclassification adjustments of benefit plan liability - prior service cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax Reclassification adjustments of benefit plan liability - net gain (loss) Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax Reclassification of net realized (gains) losses Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Net unrealized gains (losses) Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Other comprehensive income (loss), net of tax Comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Less: comprehensive income attributable to noncontrolling interest Comprehensive income available for common stock Comprehensive Income (Loss), Net of Tax, Attributable to Parent Accounts Receivable and Allowance for Doubtful Accounts Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Earnings Per Share Earnings Per Share [Text Block] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Income Statement [Abstract] Revenue Operating expenses: Operating Expenses [Abstract] Taxes - property, production and severance Taxes, Miscellaneous Other operating expenses Other Cost and Expense, Operating Total operating expenses Operating Expenses Operating income Operating Income (Loss) Other income (expense): Nonoperating Income (Expense) [Abstract] Interest charges - Interest and Debt Expense [Abstract] Interest expense incurred (including amortization of debt issuance costs, premiums and discounts) Allowance for funds used during construction - borrowed Public Utilities Allowance For Funds Used During Construction Borrowed Interest Costs Capitalized The component of the allowance for funds used during construction during the period which represents the approximate composite costs of borrowed funds and is netted against interest expense. Capitalized interest Interest Costs Capitalized Adjustment Interest income Investment Income, Interest Allowance for funds used during construction - equity Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity Other income (expense), net Other Nonoperating Income (Expense) Total other income (expense), net Nonoperating Income (Expense) Income before income taxes Income from continuing operations Net (loss) from discontinued operations Net income Net income attributable to noncontrolling interest Net Income (Loss) Attributable to Noncontrolling Interest Net income from continuing operations Net income available for common stock Earnings per share of common stock: Earnings Per Share, Basic [Abstract] Earnings Per Share, Basic [Abstract] Income from continuing operations, Basic (usd per share) Income (Loss) from Continuing Operations, Per Basic Share (Loss) from discontinued operations, Basic (usd per share) Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share Earnings (loss) per share, Basic (usd per share) Earnings Per Share, Basic Earnings Per Share, Diluted [Abstract] Earnings Per Share, Diluted [Abstract] Income from continuing operations, Diluted (usd per share) Income (Loss) from Continuing Operations, Per Diluted Share (Loss) from discontinued operations, Diluted (usd per share) Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share Earnings (loss) per share, Diluted (usd per share) Earnings Per Share, Diluted Weighted Average Number of Shares Outstanding, Basic and Diluted [Abstract] Weighted Average Number of Shares Outstanding, Basic and Diluted [Abstract] Weighted average number of shares of common stock, basic and diluted[Abstract] Basic (in shares) Diluted (in shares) Dividends declared per share of common stock (usd per share) Common Stock, Dividends, Per Share, Declared Schedule of Stockholders Equity Schedule of Stockholders Equity [Table Text Block] Crude Oil Crude Oil [Member] Natural Gas Natural Gas [Member] Options Held Options Held [Member] Swap Swap [Member] Income Taxes Income Tax Disclosure [Text Block] ASSETS Assets [Abstract] Current assets: Assets, Current [Abstract] Accounts receivable, net Accounts Receivable, Net, Current Materials, supplies and fuel Derivative assets, current Derivative Asset, Current Income tax receivable, net Income Taxes Receivable, Current Regulatory assets, current Other current assets Other Assets, Current Current assets held for sale Disposal Group, Including Discontinued Operation, Assets, Current Total current assets Assets, Current Investments Property, plant and equipment Property, Plant and Equipment, Gross Less: accumulated depreciation and depletion Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Total property, plant and equipment, net Property, Plant and Equipment, Net Other assets: Other Assets, Noncurrent [Abstract] Goodwill Goodwill Intangible assets, net Intangible Assets, Net (Excluding Goodwill) Other assets, non-current Other Assets, Noncurrent Noncurrent assets held for sale Disposal Group, Including Discontinued Operation, Assets, Noncurrent Total other assets, non-current Assets, Noncurrent, Other than Noncurrent Investments and Property, Plant and Equipment TOTAL ASSETS LIABILITIES AND TOTAL EQUITY Liabilities and Equity [Abstract] Current liabilities: Liabilities, Current [Abstract] Accounts payable Accounts Payable, Current Accrued liabilities Derivative liabilities, current Derivative Liability, Current Accrued income taxes, net Accrued Income Taxes Regulatory liabilities, current Current liabilities held for sale Disposal Group, Including Discontinued Operation, Liabilities, Current Total current liabilities Liabilities, Current Long-term debt Long-term Debt, Excluding Current Maturities Deferred credits and other liabilities: Liabilities, Noncurrent [Abstract] Deferred income tax liabilities, net Deferred Tax Liabilities, Net, Noncurrent Benefit plan liabilities Liability, Defined Benefit Plan, Noncurrent Other deferred credits and other liabilities Other Liabilities, Noncurrent Non-current liabilities held for sale Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent Total deferred credits and other liabilities Liabilities, Noncurrent Commitments and contingencies (See Notes 9, 11, 16, 17) Commitments and Contingencies Equity: Stockholders' Equity Attributable to Parent [Abstract] Common stock $1 par value; 100,000,000 shares authorized; issued 53,661,863; 53,579,986; and 53,524,529 shares, respectively Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Retained earnings Retained Earnings (Accumulated Deficit) Treasury stock, at cost – 72,915; 39,064; and 41,457 shares, respectively Treasury Stock, Value Accumulated other comprehensive income (loss) Accumulated Other Comprehensive Income (Loss), Net of Tax Total stockholders’ equity Stockholders' Equity Attributable to Parent Noncontrolling interest Noncontrolling Interest in Variable Interest Entity Total equity TOTAL LIABILITIES AND TOTAL EQUITY Liabilities and Equity Deferred Tax Assets, Goodwill and Intangible Assets Deferred Tax Assets, Goodwill and Intangible Assets Regulatory Accounting Schedule of Regulatory Assets and Liabilities [Text Block] Accrued Liabilities Accounts Payable and Accrued Liabilities Disclosure [Text Block] Public Utilities General Disclosures [Table] Public Utilities General Disclosures [Table] Wyoming Public Service Commission (WPSC) Wyoming Public Service Commission (WPSC) [Member] Wyoming Public Service Commission (WPSC) [Member] Kansas Corporation Commission Kansas Corporation Commission [Member] Kansas Corporation Commission Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Black Hills Energy, Rocky Mountain Natural Gas Black Hills Energy, Rocky Mountain Natural Gas [Member] Black Hills Energy, Rocky Mountain Natural Gas [Member] Black Hills Energy, Wyoming Gas Black Hills Energy, Wyoming Gas [Member] Black Hills Energy, Wyoming Gas [Member] Black Hills Energy, Arkansas Black Hills Energy, Arkansas [Member] Black Hills Energy, Arkansas [Member] Black Hills Energy, Wyoming Electric Black Hills Energy, Wyoming Electric [Member] Black Hills Energy, Wyoming Electric [Member] Black Hills Gas Distribution - Nebraska Black Hills Gas Distribution - Nebraska [Member] Black Hills Gas Distribution - Nebraska [Member] Black Hills Energy, Kansas Black Hills Energy, Kansas [Member] Black Hills Energy, Kansas [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Maximum Maximum [Member] Public Utilities, General Disclosures [Line Items] Public Utilities, General Disclosures [Line Items] Approved revenue increase Public Utilities, Approved Rate Increase (Decrease), Amount Return on equity Public Utilities, Approved Return on Equity, Percentage Capital structure, equity Public Utilities, Approved Equity Capital Structure, Percentage Capital structure, debt Public Utilities, Approved Debt Capital Structure, Percentage Public Utilities, Amount Of Existing Revenue Collected Through Rider Mechanisms Included In New Base Rates Public Utilities, Amount Of Existing Revenue Collected Through Rider Mechanisms Included In New Base Rates Public Utilities, Amount Of Existing Revenue Collected Through Rider Mechanisms Included In New Base Rates Public Utilities, Aggregate Amount of Customer Credits Through The Power Cost Adjustment Mechanism Public Utilities, Aggregate Amount of Customer Credits Through The Power Cost Adjustment Mechanism Public Utilities, Aggregate Amount of Customer Credits Through The Power Cost Adjustment Mechanism Public Utilities, Power Purchase Agreement Annual Cost Escalation Percentage Through 2022 Public Utilities, Power Purchase Agreement Annual Cost Escalation Percentage Through 2022 Public Utilities, Power Purchase Agreement Annual Cost Escalation Percentage Through 2022 Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Accounts Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts Receivable, Trade Accounts Receivable, Gross, Current Unbilled Receivables, Current Unbilled Receivables, Current Allowance for Doubtful Accounts Allowance for Doubtful Accounts Receivable, Current Accounts receivable, net Schedule of Fair Value Hierarchy, Measured on Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Schedule of Derivative Instruments Balance Sheet Location Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent AOCI Attributable to Parent AOCI Attributable to Parent [Member] Interest Rate Swaps Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] AOCI Attributable to Parent, Net of Tax [Roll Forward] Accumulated Other Comprehensive Income [Roll Forward] Accumulated Other Comprehensive Income [Roll Forward] Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Reclassification from AOCI, Current Period, Tax Reclassification from AOCI, Current Period, Tax Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End Line of Credit Facility [Table] Line of Credit Facility [Table] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Consolidated Indebtedness to Capitalization Ratio Debt Instrument, Consolidated Indebtedness To Capitalization Ratio Requirement For The Next Fiscal Year Debt Instrument, Consolidated Indebtedness To Capitalization Ratio Requirement For The Next Fiscal Year Recourse Leverage Ratio Recourse Leverage Ratio Recourse Leverage Ratio Debt instrument, covenant, Leverage Recourse Ratio Debt Instrument, Covenant, Recourse Leverage Ratio The maximum allowed recourse leverage ratio under debt covenants.