Income Tax Disclosure [Abstract] Income Taxes Income Tax 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 Statement of Stockholders' Equity [Abstract] Schedule of Stockholders Equity Schedule of Stockholders Equity [Table Text Block] Schedule of Variable Interest Entities Schedule of Variable Interest Entities [Table Text Block] Equity Stockholders' Equity Note Disclosure [Text Block] Debt Disclosure [Abstract] Notes Payable and Long-term Debt Debt Disclosure [Text Block] Inventory, Net [Abstract] Materials, Supplies and Fuel Schedule of Inventory, Current [Table Text Block] Fair Value Disclosures [Abstract] Fair Value of Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Statement of Comprehensive Income [Abstract] Statement [Table] Statement [Table] 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 Revenue Revenue, Net 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 Segment Reporting Information, Additional Information [Abstract] Reconciliation of Assets from Segment to Consolidated [Table] Reconciliation of Assets from Segment to Consolidated [Table] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Discontinued Operations, Held-for-sale Discontinued Operations, Held-for-sale [Member] Segments [Axis] Segments [Axis] Segment [Domain] Segments [Domain] Electric Utilities Electric Utilities [Member] Electric Utilities Segment [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] Corporate Corporate, Non-Segment [Member] Segment Reporting, Asset Reconciling Item [Line Items] Segment Reporting, Asset Reconciling Item [Line Items] Assets Assets 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. 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 Interest Rate Swap [Member] 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 Accumulated Other Comprehensive Income (Loss), Net of Tax 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 Commitments and Contingencies Disclosure [Abstract] 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. 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] 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 Discontinued Operations and Disposal Groups [Abstract] Discontinued Operations Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] 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 Other Comprehensive Income (Loss) Comprehensive Income (Loss) Note [Text Block] 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] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] Base Rate Base Rate [Member] Eurodollar Eurodollar [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 Receivables [Abstract] Accounts Receivable Loans, Notes, Trade and Other Receivables Disclosure [Text Block] 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] Income Statement [Abstract] Operating expenses: Operating Expenses [Abstract] Depreciation, depletion and amortization Depreciation, Depletion and Amortization 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 Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Net (loss) from discontinued operations Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent Net income Net income attributable to noncontrolling interest Net Income (Loss) Attributable to Noncontrolling Interest Net income from continuing operations Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Net income available for common stock Net Income (Loss) Available to Common Stockholders, Basic Earnings per share of common stock: Earnings Per Share [Abstract] 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) Weighted Average Number of Shares Outstanding, Basic Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Dividends declared per share of common stock (usd per share) Common Stock, Dividends, Per Share, Declared Derivative Instruments and Hedging Activities Disclosure [Abstract] Risk Management Activities Derivative Instruments and Hedging Activities Disclosure [Text Block] Net income available for common stock Weighted average shares - basic (in shares) 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) Interest rate swaps Statement [Line Items] Statement [Line Items] 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 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] Sales Revenue, Net Sales Revenue, Net [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] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Designated as Hedging Instrument Designated as Hedging Instrument [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 Line of Credit Facility [Table] Line of Credit Facility [Table] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Maximum Maximum [Member] 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. Defined Benefit Plan [Abstract] Employee Benefit Plans Pension and Other Postretirement Benefits Disclosure [Text Block] Materials, Supplies and Fuel Inventory Disclosure [Text Block] Long-term Investments [Abstract] Investments Investment [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 Supplemental Cash Flow Information [Abstract] Supplemental Disclosure of Cash Flow Information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] 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] Regulatory Liability [Axis] Regulatory Liability [Axis] Regulatory Liability [Domain] Regulatory Liability [Domain] 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 Revenue Subject to Refund [Member] 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] Maximum Amortization (in years) Regulatory Asset, Amortization Period 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] Maximum Amortization (in years) Regulatory Liability, Amortization Period Regulatory liabilities Regulatory Liabilities Less current regulatory liabilities Regulatory Liability, Current Regulatory liabilities, non-current Regulatory Liability, Noncurrent Estimated and recorded revenue reduction from TCJA tax benefits Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Schedule of Accrued Liabilities Schedule of Accrued Liabilities [Table Text Block] Subsequent Event [Table] Subsequent Event [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Subsequent Event [Line Items] Subsequent Event [Line Items] Percent of Properties Having Either Closed Transactions or Signed Contracts to Sell Disposal Group, Including Discontinued Operations, Percent of Properties Having Either Closed Transactions or Signed Contracts to Sell Disposal Group, Including Discontinued Operations, Percent of Properties Having Either Closed Transactions or Signed Contracts to Sell 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 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) Other noncurrent liabilities Disposal Group, Including Discontinued Operation, Other Liabilities, Noncurrent Net liabilities Disposal Group, Including Discontinued Operation, Liabilities Net assets Disposal Group, Including Discontinued Operation, Assets Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract] Revenue Disposal Group, Including Discontinued Operation, Revenue Operations and maintenance Disposal Group, Including Discontinued Operation, Operating Expense Depreciation, depletion and amortization Disposal Group, Including Discontinued Operation, Depreciation and Amortization Total operating expenses Disposal Group, Including Discontinued Operations, Total Operating Expenses Disposal Group, Including Discontinued Operations, Total Operating Expenses Operating (loss) Disposal Group, Including Discontinued Operation, Operating Income (Loss) Other income (expense), net Disposal Group, Including Discontinued Operations, Other Income (Expense), net Disposal Group, Including Discontinued Operations, Other Income (Expense), net Income tax benefit (expense) Discontinued Operation, Tax Effect of Discontinued Operation (Loss) from discontinued operations 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] Restructuring Type [Axis] Restructuring Type [Axis] Type of Restructuring [Domain] Type of Restructuring [Domain] Other Restructuring Other Restructuring [Member] Deferred Tax Assets, Goodwill and Intangible Assets Deferred Tax Assets, Goodwill and Intangible Assets Deferred income taxes Deferred Income Tax Expense (Benefit) Accrued Liabilities Accounts Payable and Accrued Liabilities Disclosure [Text Block] Accounts Receivable and Allowance for Doubtful Accounts Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Management's Statement Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Black Hills Corporation Black Hills Corporation [Member] Black Hills Corporation [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] 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] Debt Instrument [Line Items] Debt Instrument [Line Items] Current maturities of long-term debt Long-term Debt, Current Maturities 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 Noncontrolling interest Effective Income Tax Rate Reconciliation, Noncontrolling Interest Income (Loss), Percent IRC 172(f) carryback claim Effective Income Tax Reconciliation Net Operating Loss Carryback Effective Income Tax Reconciliation Net Operating Loss Carryback 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 Tax benefit related to legal restructuring 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 ASSETS Assets [Abstract] Current assets: Assets, Current [Abstract] Accounts receivable, net Accounts Receivable, Net, Current Materials, supplies and fuel Inventory, Net 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 Long-term 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 53,648,817; 53,579,986; and 53,502,252 shares, respectively Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Retained earnings Retained Earnings (Accumulated Deficit) Treasury stock, at cost – 53,959; 39,064; and 41,443 shares, respectively Treasury Stock, Value Accumulated other comprehensive income (loss) Total stockholders’ equity Stockholders' Equity Attributable to Parent Noncontrolling interest Noncontrolling Interest in Variable Interest Entity Total equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest TOTAL LIABILITIES AND TOTAL EQUITY Liabilities and Equity Fair Value Measurements Derivatives and Fair Value [Text Block] Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] 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) Business Segment Information Segment Reporting Disclosure [Text Block] 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 Public Utilities General Disclosures [Table] Public Utilities General Disclosures [Table] Regulatory Agency [Axis] Regulatory Agency [Axis] Regulatory Agency [Domain] Regulatory Agency [Domain] Colorado Public Utilities Commission (CPUC) Colorado Public Utilities Commission (CPUC) [Member] Colorado Public Utilities Commission (CPUC) [Member] Black Hills Energy, Rocky Mountain Natural Gas Black Hills Energy, Rocky Mountain Natural Gas [Member] Black Hills Energy, Rocky Mountain Natural Gas [Member] Public Utilities, General Disclosures [Line Items] Public Utilities, General Disclosures [Line Items] Annual revenue increases and an extension of SSIR 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 Derivative Expired During the Period Derivative Expired During the Period Derivative Expired During the Period Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] 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 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