2.2.0.7 true Consolidated Statements of Cash Flows (Unaudited) (USD $) 0130 - Statement - Consolidated Statements of Cash Flows (Unaudited) true false In Thousands false false 1 USD true false false false WGL Holdings, Inc. dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_ParentCompanyMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 $ false 2 USD true false false false WGL Holdings, Inc. dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_ParentCompanyMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 $ 1 WGL Holdings, Inc. 0 na true na na No definition available. false true false false false false false false false false false http://wglholdings.com/role/statementsofcashflows false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false false 1 USD true false false false WGL Holdings, Inc. dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_ParentCompanyMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 $ false 2 USD true false false false WGL Holdings, Inc. dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_ParentCompanyMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 $ false 1 USD true false false false WGL Holdings, Inc. dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_ParentCompanyMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 $ false 2 USD true false false false WGL Holdings, Inc. dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_ParentCompanyMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 $ na No definition available. No authoritative reference available. false 2 OPERATING ACTIVITIES 2 us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string The net cash from (used in) all of the entity's operating activities, including those of discontinued operations, of the reporting entity. Operating activities include all transactions and events that are not defined as investing or financing activities. Operating activities generally involve producing and delivering goods and providing services. Cash flows from operating activities are generally the cash effects of transactions and other events that enter into the determination of net income. false 3 Net income before preferred stock dividends 2 us-gaap_NetIncomeLoss us-gaap true credit duration No definition available. false false false false false false false false false false false terselabel false 1 true true false false 137018000 137018 false false false 2 true true false false 132492000 132492 false false false xbrli:monetaryItemType monetary The portion of consolidated profit or loss for the period, net of income taxes, which is attributable to the parent. If the entity does not present consolidated financial statements, the amount of profit or loss for the period, net of income taxes. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 19 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph d Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A7 -Appendix A Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph a Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 20 -Article 9 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 10, 15 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 87-21 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28, 29, 30 false 4 ADJUSTMENTS TO RECONCILE NET INCOME TO NET CASH PROVIDED BY OPERATING ACTIVITIES 2 us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 5 Depreciation and amortization 2 us-gaap_UtilitiesOperatingExpenseDepreciationAndAmortization us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 72032000 72032 false false false 2 false true false false 71494000 71494 false false false xbrli:monetaryItemType monetary Discloses the amount of operating expense for the period related to depreciation and amortization. No authoritative reference available. false 6 Amortization of: 2 us-gaap_AdjustmentForAmortizationAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 7 Other regulatory assets and liabilities-net 2 wgl_OtherRegulatoryAssetsAndLiabilitiesNet wgl false debit duration Other regulatory assets and liabilities net. false false false false false false false false false false false verboselabel false 1 false true false false 2957000 2957 false false false 2 false true false false 2463000 2463 false false false xbrli:monetaryItemType monetary Other regulatory assets and liabilities net. No authoritative reference available. false 8 Debt related costs 2 us-gaap_AmortizationOfFinancingCostsAndDiscounts us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 570000 570 false false false 2 false true false false 561000 561 false false false xbrli:monetaryItemType monetary The component of interest expense representing the noncash expenses charged against earnings in the period to allocate debt discount and premium, and the costs to issue debt and obtain financing over the related debt instruments. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 9 Deferred income taxes-net 2 us-gaap_DeferredIncomeTaxExpenseBenefit us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 75043000 75043 false false false 2 false true false false 21975000 21975 false false false xbrli:monetaryItemType monetary The component of income tax expense for the period representing the net change in the entity's deferred tax assets and liabilities pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 6 -Section I -Subsection 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 45 -Subparagraph b Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 289 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Article 4 false 10 Accrued/deferred pension cost (income) 2 wgl_AccruedDeferredPensionCost wgl false debit duration Accrued/deferred pension cost. false false false false false false false false false false false verboselabel false 1 false true false false 8798000 8798 false false false 2 false true false false -3149000 -3149 false false false xbrli:monetaryItemType monetary Accrued/deferred pension cost. No authoritative reference available. false 11 Compensation expense related to equity awards 2 us-gaap_ShareBasedCompensation us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 1812000 1812 false false false 2 false true false false 1543000 1543 false false false xbrli:monetaryItemType monetary The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock options, amortization of restricted stock, and adjustment for officers compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 12 Provision for doubtful accounts 2 us-gaap_ProvisionForDoubtfulAccounts us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 13739000 13739 false false false 2 false true false false 16713000 16713 false false false xbrli:monetaryItemType monetary Amount of the current period expense charged against operations, the offset which is generally to the allowance for doubtful accounts for the purpose of reducing receivables, including notes receivable, to an amount that approximates their net realizable value (the amount expected to be collected). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 5 -Article 5 false 13 Other non-cash charges (credits)-net 2 us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesOther us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -144000 -144 false false false 2 false true false false -541000 -541 false false false xbrli:monetaryItemType monetary Transactions that do not result in cash inflows or outflows in the period in which they occur, but affect net income and thus are removed when calculating net cash flow from operating activities using the indirect cash flow method. This element is used when there is not a more specific and appropriate element. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 14 CHANGES IN ASSETS AND LIABILITIES 2 us-gaap_IncreaseDecreaseInOperatingCapitalAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 15 Accounts receivable and unbilled revenues-net 2 us-gaap_IncreaseDecreaseInAccountsAndOtherReceivables us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -78638000 -78638 false false false 2 false true false false -54767000 -54767 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the amount due from customers for the credit sale of goods and services; includes accounts receivable and other types of receivables. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 16 Gas costs and other regulatory assets/liabilities-net 2 us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false 54484000 54484 false false false 2 false true false false 35337000 35337 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the value of assets that are created when regulatory agencies permits public utilities to defer costs (revenues) to the balance sheet. This element is a the net change of regulatory assets and liabilities combined. No authoritative reference available. false 17 Storage gas 2 us-gaap_IncreaseDecreaseInInventories us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false 80796000 80796 false false false 2 false true false false 249841000 249841 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the aggregate value of all inventory held by the reporting entity, associated with underlying transactions that are classified as operating activities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 18 Other prepayments 2 us-gaap_IncreaseDecreaseInPrepaidExpense us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false 11084000 11084 false false false 2 false true false false -27175000 -27175 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the amount of outstanding money paid in advance for goods or services that bring economic benefits for future periods. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 19 Accounts payable and other accrued liabilities 2 us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -9603000 -9603 false false false 2 false true false false -35129000 -35129 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the aggregate amount of obligations and expenses incurred but not paid. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 20 Wages payable 2 us-gaap_IncreaseDecreaseInAccruedSalaries us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 3453000 3453 false false false 2 false true false false 3263000 3263 false false false xbrli:monetaryItemType monetary Net change during the period in the amount of salaries accrued at the period end. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 21 Customer deposits and advance payments 2 wgl_CustomerDepositsAndAdvancePayments wgl false debit duration Customer deposits and advance payments false false false false false false false false false false false verboselabel false 1 false true false false -9752000 -9752 false false false 2 false true false false -3112000 -3112 false false false xbrli:monetaryItemType monetary Customer deposits and advance payments No authoritative reference available. false 22 Accrued taxes 2 us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 2783000 2783 false false false 2 false true false false 28270000 28270 false false false xbrli:monetaryItemType monetary The net change during the period in the amount of cash payments due to taxing authorities for taxes that are based on the reporting entity's earnings. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 23 Accrued interest 2 us-gaap_IncreaseDecreaseInInterestPayableNet us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 8405000 8405 false false false 2 false true false false 9692000 9692 false false false xbrli:monetaryItemType monetary The net change during the reporting period in interest payable, which represents the amount owed to note holders, bond holders, and other parties for interest earned on loans or credit extended to the reporting entity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 24 Other current assets 2 us-gaap_IncreaseDecreaseInOtherOperatingAssets us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -3001000 -3001 false false false 2 false true false false -6748000 -6748 false false false xbrli:monetaryItemType monetary The net change during the reporting period in other operating assets not otherwise defined in the taxonomy. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 25 Other current liabilities 2 us-gaap_IncreaseDecreaseInOtherOperatingLiabilities us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 10945000 10945 false false false 2 false true false false -16390000 -16390 false false false xbrli:monetaryItemType monetary The net change during the reporting period in other operating obligations not otherwise defined in the taxonomy. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 26 Deferred gas costs-net 2 us-gaap_IncreaseDecreaseInDeferredGasCost us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false 29946000 29946 false false false 2 false true false false -15542000 -15542 false false false xbrli:monetaryItemType monetary The net change during the reporting period in carrying amount of capitalized gas costs of a regulated entity that are expected to be recoverable through rate adjustments within one year or the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 27 Deferred assets-other 2 us-gaap_IncreaseDecreaseInDeferredCharges us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -41692000 -41692 false false false 2 false true false false -17480000 -17480 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the value of expenditures made during the current reporting period for benefits that will be received over a period of years. Deferred charges differ from prepaid expenses in that they usually extend over a long period of time and may or may not be regularly recurring costs of operation. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 28 Deferred liabilities-other 2 us-gaap_IncreaseDecreaseInOtherDeferredLiability us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -2418000 -2418 false false false 2 false true false false -1822000 -1822 false false false xbrli:monetaryItemType monetary The net change during the reporting period in other obligations not otherwise defined in the taxonomy where the payments will be made in future periods. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 29 Other-net 2 us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet us-gaap true credit duration No definition available. false false false false false false false false false false true negatedtotal false 1 false true false false 91000 91 false false false 2 false true false false 2549000 2549 false false false xbrli:monetaryItemType monetary For entities with classified balance sheets, the net change during the reporting period in the value of other assets or liabilities used in operating activities, that are not otherwise defined in the taxonomy. For entities with unclassified balance sheets, the net change during the reporting period in the value of all other assets or liabilities used in operating activities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 true 30 Net Cash Provided by Operating Activities 2 us-gaap_NetCashProvidedByUsedInOperatingActivities us-gaap true na duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false 368708000 368708 false false false 2 false true false false 394338000 394338 false false false xbrli:monetaryItemType monetary The net cash from (used in) all of the entity's operating activities, including those of discontinued operations, of the reporting entity. Operating activities generally involve producing and delivering goods and providing services. Operating activity cash flows include transactions, adjustments, and changes in value that are not defined as investing or financing activities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 true 31 FINANCING ACTIVITIES 2 us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 32 Common stock issued 2 us-gaap_ProceedsFromIssuanceOfCommonStock us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 14141000 14141 false false false 2 false true false false 5070000 5070 false false false xbrli:monetaryItemType monetary The cash inflow from the additional capital contribution to the entity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 19 -Subparagraph a false 33 Long-term debt issued 2 us-gaap_ProceedsFromIssuanceOfLongTermDebt us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 51502000 51502 false false false 2 false true false false 61458000 61458 false false false xbrli:monetaryItemType monetary The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 19 -Subparagraph b false 34 Long-term debt retired 2 us-gaap_RepaymentsOfLongTermDebt us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -74379000 -74379 false false false 2 false true false false -26012000 -26012 false false false xbrli:monetaryItemType monetary The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 20 -Subparagraph b false 35 Debt issuance costs 2 us-gaap_PaymentsOfDebtIssuanceCosts us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -330000 -330 false false false 2 false false false false 0 0 false false false xbrli:monetaryItemType monetary The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 95-13 false 36 Notes payable issued (retired)-net 2 us-gaap_ProceedsFromRepaymentsOfShortTermDebt us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -176789000 -176789 false false false 2 false true false false -248896000 -248896 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) for borrowing having initial term of repayment within one year or the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 false 37 Dividends on common stock and preferred stock 2 us-gaap_PaymentsOfOrdinaryDividends us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -57048000 -57048 false false false 2 false true false false -54949000 -54949 false false false xbrli:monetaryItemType monetary The cash outflow from distribution of an entity's earnings to common and preferred stockholders, including minority shareholders. This element excludes special dividends, which are included in a separate element for capital distributions. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 20 -Subparagraph a false 38 Other financing activities-net 2 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities us-gaap true debit duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false -894000 -894 false false false 2 false true false false -839000 -839 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) from other financing activities. This element is used when there is not a more specific and appropriate element in the taxonomy. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18, 19, 20 true 39 Net Cash Used in Financing Activities 2 us-gaap_NetCashProvidedByUsedInFinancingActivities us-gaap true debit duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false -243797000 -243797 false false false 2 false true false false -264168000 -264168 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) from financing activity for the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 true 40 INVESTING ACTIVITIES 2 us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 41 Capital expenditures (excluding Allowance for Funds Used During Construction) 2 us-gaap_PaymentsToAcquireProductiveAssets us-gaap true credit duration No definition available. false false false false false false false false false false true negatedtotal false 1 false true false false -84473000 -84473 false false false 2 false true false false -94705000 -94705 false false false xbrli:monetaryItemType monetary The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 17 -Subparagraph c true 42 Net Cash Used in Investing Activities 2 us-gaap_NetCashProvidedByUsedInInvestingActivities us-gaap true debit duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false -84473000 -84473 false false false 2 false true false false -94705000 -94705 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) from investing activity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 true 43 INCREASE IN CASH AND CASH EQUIVALENTS 2 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease us-gaap true na duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 40438000 40438 false false false 2 false true false false 35465000 35465 false false false xbrli:monetaryItemType monetary The net change between the beginning and ending balance of cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 false 44 Cash and Cash Equivalents at Beginning of Year 2 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant No definition available. false false false false false false false false true false false periodstartlabel false 1 false true false false 7845000 7845 false false false 2 false true false false 6164000 6164 false false false xbrli:monetaryItemType monetary Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits should not be reported as cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 26 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8, 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 false 45 Cash and Cash Equivalents at End of Year 2 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant No definition available. false false false false false false false false false true false periodendlabel false 1 false true false false 48283000 48283 false false false 2 false true false false 41629000 41629 false false false xbrli:monetaryItemType monetary Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits should not be reported as cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 26 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8, 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 false 46 SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION 2 us-gaap_SupplementalCashFlowInformationAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 47 Income taxes paid 2 us-gaap_IncomeTaxesPaid us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 49662000 49662 false false false 2 false true false false 40763000 40763 false false false xbrli:monetaryItemType monetary The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 29 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 27 -Subparagraph f false 48 Interest paid 2 us-gaap_InterestPaid us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 21182000 21182 false false false 2 false true false false 24173000 24173 false false false xbrli:monetaryItemType monetary The amount of cash paid during the current period for interest owed on money borrowed; includes amount of interest capitalized Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 29 false 49 SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING ACTIVITIES 2 us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string Designated to encapsulate the entire footnote disclosure that gives information on the supplemental cash flow activities for noncash (or part noncash) transactions for the period. Noncash is defined as information about all investing and financing activities of an enterprise during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. false 50 Extinguishment of project debt financing 2 us-gaap_ExtinguishmentOfDebtAmount us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false true false false 7375000 7375 false false false xbrli:monetaryItemType monetary Gross amount of debt extinguished. No authoritative reference available. false 51 Capital expenditures included in accounts payable and other accrued liabilities 2 us-gaap_CapitalExpendituresIncurredButNotYetPaid us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 3218000 3218 false false false 2 false true false false 5199000 5199 false false false xbrli:monetaryItemType monetary Future cash outflow to pay for purchases of fixed assets that have occurred. No authoritative reference available. false 52 Washington Gas Light Company 0 na true na na No definition available. false true false false false false false false false false false http://wglholdings.com/role/statementsofcashflows false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false false 5 USD true false false false Washington Gas Light Company dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_SubsidiariesMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ false 6 USD true false false false Washington Gas Light Company dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_SubsidiariesMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ false 7 USD true false false false Washington Gas Light Company dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_SubsidiariesMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ false 8 USD true false false false Washington Gas Light Company dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_SubsidiariesMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ na No definition available. No authoritative reference available. false 53 OPERATING ACTIVITIES 2 us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string The net cash from (used in) all of the entity's operating activities, including those of discontinued operations, of the reporting entity. Operating activities include all transactions and events that are not defined as investing or financing activities. Operating activities generally involve producing and delivering goods and providing services. Cash flows from operating activities are generally the cash effects of transactions and other events that enter into the determination of net income. false 54 Net income before preferred stock dividends 2 us-gaap_NetIncomeLoss us-gaap true credit duration No definition available. false false false false false false false false false false false terselabel false 1 false true false false 121599000 121599 false false false 2 false true false false 127214000 127214 false false false xbrli:monetaryItemType monetary The portion of consolidated profit or loss for the period, net of income taxes, which is attributable to the parent. If the entity does not present consolidated financial statements, the amount of profit or loss for the period, net of income taxes. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 19 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph d Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A7 -Appendix A Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph a Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 20 -Article 9 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 10, 15 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 87-21 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28, 29, 30 false 55 ADJUSTMENTS TO RECONCILE NET INCOME TO NET CASH PROVIDED BY OPERATING ACTIVITIES 2 us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 56 Depreciation and amortization 2 us-gaap_UtilitiesOperatingExpenseDepreciationAndAmortization us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 70610000 70610 false false false 2 false true false false 70130000 70130 false false false xbrli:monetaryItemType monetary Discloses the amount of operating expense for the period related to depreciation and amortization. No authoritative reference available. false 57 Amortization of: 2 us-gaap_AdjustmentForAmortizationAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 58 Other regulatory assets and liabilities-net 2 wgl_OtherRegulatoryAssetsAndLiabilitiesNet wgl false debit duration Other regulatory assets and liabilities net. false false false false false false false false false false false verboselabel false 1 false true false false 2957000 2957 false false false 2 false true false false 2463000 2463 false false false xbrli:monetaryItemType monetary Other regulatory assets and liabilities net. No authoritative reference available. false 59 Debt related costs 2 us-gaap_AmortizationOfFinancingCostsAndDiscounts us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 570000 570 false false false 2 false true false false 597000 597 false false false xbrli:monetaryItemType monetary The component of interest expense representing the noncash expenses charged against earnings in the period to allocate debt discount and premium, and the costs to issue debt and obtain financing over the related debt instruments. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 60 Deferred income taxes-net 2 us-gaap_DeferredIncomeTaxExpenseBenefit us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 77983000 77983 false false false 2 false true false false 29543000 29543 false false false xbrli:monetaryItemType monetary The component of income tax expense for the period representing the net change in the entity's deferred tax assets and liabilities pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 6 -Section I -Subsection 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 45 -Subparagraph b Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 289 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Article 4 false 61 Accrued/deferred pension cost (income) 2 wgl_AccruedDeferredPensionCost wgl false debit duration Accrued/deferred pension cost. false false false false false false false false false false false verboselabel false 1 false true false false 8133000 8133 false false false 2 false true false false -3294000 -3294 false false false xbrli:monetaryItemType monetary Accrued/deferred pension cost. No authoritative reference available. false 62 Compensation expense related to equity awards 2 us-gaap_ShareBasedCompensation us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 1737000 1737 false false false 2 false true false false 1468000 1468 false false false xbrli:monetaryItemType monetary The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock options, amortization of restricted stock, and adjustment for officers compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 63 Provision for doubtful accounts 2 us-gaap_ProvisionForDoubtfulAccounts us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 10701000 10701 false false false 2 false true false false 13772000 13772 false false false xbrli:monetaryItemType monetary Amount of the current period expense charged against operations, the offset which is generally to the allowance for doubtful accounts for the purpose of reducing receivables, including notes receivable, to an amount that approximates their net realizable value (the amount expected to be collected). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 5 -Article 5 false 64 Other non-cash charges (credits)-net 2 us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesOther us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -850000 -850 false false false 2 false true false false -840000 -840 false false false xbrli:monetaryItemType monetary Transactions that do not result in cash inflows or outflows in the period in which they occur, but affect net income and thus are removed when calculating net cash flow from operating activities using the indirect cash flow method. This element is used when there is not a more specific and appropriate element. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 65 CHANGES IN ASSETS AND LIABILITIES 2 us-gaap_IncreaseDecreaseInOperatingCapitalAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 66 Accounts receivable and unbilled revenues-net 2 us-gaap_IncreaseDecreaseInAccountsAndOtherReceivables us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -38539000 -38539 false false false 2 false true false false -22973000 -22973 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the amount due from customers for the credit sale of goods and services; includes accounts receivable and other types of receivables. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 67 Gas costs and other regulatory assets/liabilities-net 2 us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false 54484000 54484 false false false 2 false true false false 35337000 35337 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the value of assets that are created when regulatory agencies permits public utilities to defer costs (revenues) to the balance sheet. This element is a the net change of regulatory assets and liabilities combined. No authoritative reference available. false 68 Storage gas 2 us-gaap_IncreaseDecreaseInInventories us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false 51078000 51078 false false false 2 false true false false 199695000 199695 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the aggregate value of all inventory held by the reporting entity, associated with underlying transactions that are classified as operating activities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 69 Other prepayments 2 us-gaap_IncreaseDecreaseInPrepaidExpense us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -14438000 -14438 false false false 2 false true false false 22366000 22366 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the amount of outstanding money paid in advance for goods or services that bring economic benefits for future periods. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 70 Accounts payable and other accrued liabilities 2 us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -15583000 -15583 false false false 2 false true false false -53391000 -53391 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the aggregate amount of obligations and expenses incurred but not paid. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 71 Wages payable 2 us-gaap_IncreaseDecreaseInAccruedSalaries us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 3223000 3223 false false false 2 false true false false 3050000 3050 false false false xbrli:monetaryItemType monetary Net change during the period in the amount of salaries accrued at the period end. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 72 Customer deposits and advance payments 2 wgl_CustomerDepositsAndAdvancePayments wgl false debit duration Customer deposits and advance payments false false false false false false false false false false false verboselabel false 1 false true false false -9752000 -9752 false false false 2 false true false false -3361000 -3361 false false false xbrli:monetaryItemType monetary Customer deposits and advance payments No authoritative reference available. false 73 Accrued taxes 2 us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 1967000 1967 false false false 2 false true false false 19874000 19874 false false false xbrli:monetaryItemType monetary The net change during the period in the amount of cash payments due to taxing authorities for taxes that are based on the reporting entity's earnings. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 74 Accrued interest 2 us-gaap_IncreaseDecreaseInInterestPayableNet us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 8405000 8405 false false false 2 false true false false 9692000 9692 false false false xbrli:monetaryItemType monetary The net change during the reporting period in interest payable, which represents the amount owed to note holders, bond holders, and other parties for interest earned on loans or credit extended to the reporting entity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 75 Other current assets 2 us-gaap_IncreaseDecreaseInOtherOperatingAssets us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false 2033000 2033 false false false 2 false true false false -8463000 -8463 false false false xbrli:monetaryItemType monetary The net change during the reporting period in other operating assets not otherwise defined in the taxonomy. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 76 Other current liabilities 2 us-gaap_IncreaseDecreaseInOtherOperatingLiabilities us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -1231000 -1231 false false false 2 false true false false -24459000 -24459 false false false xbrli:monetaryItemType monetary The net change during the reporting period in other operating obligations not otherwise defined in the taxonomy. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 77 Deferred gas costs-net 2 us-gaap_IncreaseDecreaseInDeferredGasCost us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false 29946000 29946 false false false 2 false true false false -15542000 -15542 false false false xbrli:monetaryItemType monetary The net change during the reporting period in carrying amount of capitalized gas costs of a regulated entity that are expected to be recoverable through rate adjustments within one year or the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 78 Deferred assets-other 2 us-gaap_IncreaseDecreaseInDeferredCharges us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -32053000 -32053 false false false 2 false true false false -12132000 -12132 false false false xbrli:monetaryItemType monetary The net change during the reporting period in the value of expenditures made during the current reporting period for benefits that will be received over a period of years. Deferred charges differ from prepaid expenses in that they usually extend over a long period of time and may or may not be regularly recurring costs of operation. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 79 Deferred liabilities-other 2 us-gaap_IncreaseDecreaseInOtherDeferredLiability us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -7295000 -7295 false false false 2 false true false false -18540000 -18540 false false false xbrli:monetaryItemType monetary The net change during the reporting period in other obligations not otherwise defined in the taxonomy where the payments will be made in future periods. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 false 80 Other-net 2 us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet us-gaap true credit duration No definition available. false false false false false false false false false false true negatedtotal false 1 false true false false 292000 292 false false false 2 false true false false 2499000 2499 false false false xbrli:monetaryItemType monetary For entities with classified balance sheets, the net change during the reporting period in the value of other assets or liabilities used in operating activities, that are not otherwise defined in the taxonomy. For entities with unclassified balance sheets, the net change during the reporting period in the value of all other assets or liabilities used in operating activities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 true 81 Net Cash Provided by Operating Activities 2 us-gaap_NetCashProvidedByUsedInOperatingActivities us-gaap true na duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false 325977000 325977 false false false 2 false true false false 374705000 374705 false false false xbrli:monetaryItemType monetary The net cash from (used in) all of the entity's operating activities, including those of discontinued operations, of the reporting entity. Operating activities generally involve producing and delivering goods and providing services. Operating activity cash flows include transactions, adjustments, and changes in value that are not defined as investing or financing activities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 true 82 FINANCING ACTIVITIES 2 us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 84 Long-term debt issued 2 us-gaap_ProceedsFromIssuanceOfLongTermDebt us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 51502000 51502 false false false 2 false true false false 61458000 61458 false false false xbrli:monetaryItemType monetary The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 19 -Subparagraph b false 85 Long-term debt retired 2 us-gaap_RepaymentsOfLongTermDebt us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -74379000 -74379 false false false 2 false true false false -25018000 -25018 false false false xbrli:monetaryItemType monetary The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 20 -Subparagraph b false 86 Debt issuance costs 2 us-gaap_PaymentsOfDebtIssuanceCosts us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -330000 -330 false false false 2 false false false false 0 0 false false false xbrli:monetaryItemType monetary The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 95-13 false 87 Notes payable issued (retired)-net 2 us-gaap_ProceedsFromRepaymentsOfShortTermDebt us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false -124791000 -124791 false false false 2 false true false false -230995000 -230995 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) for borrowing having initial term of repayment within one year or the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 false 88 Dividends on common stock and preferred stock 2 us-gaap_PaymentsOfOrdinaryDividends us-gaap true credit duration No definition available. false false false false false false false false false false true negated false 1 false true false false -54794000 -54794 false false false 2 false true false false -53450000 -53450 false false false xbrli:monetaryItemType monetary The cash outflow from distribution of an entity's earnings to common and preferred stockholders, including minority shareholders. This element excludes special dividends, which are included in a separate element for capital distributions. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 20 -Subparagraph a false 89 Other financing activities-net 2 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities us-gaap true debit duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false -788000 -788 false false false 2 false true false false -831000 -831 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) from other financing activities. This element is used when there is not a more specific and appropriate element in the taxonomy. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18, 19, 20 true 90 Net Cash Used in Financing Activities 2 us-gaap_NetCashProvidedByUsedInFinancingActivities us-gaap true debit duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false -203580000 -203580 false false false 2 false true false false -248836000 -248836 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) from financing activity for the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 true 91 INVESTING ACTIVITIES 2 us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 92 Capital expenditures (excluding Allowance for Funds Used During Construction) 2 us-gaap_PaymentsToAcquireProductiveAssets us-gaap true credit duration No definition available. false false false false false false false false false false true negatedtotal false 1 false true false false -80915000 -80915 false false false 2 false true false false -91334000 -91334 false false false xbrli:monetaryItemType monetary The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 17 -Subparagraph c true 93 Net Cash Used in Investing Activities 2 us-gaap_NetCashProvidedByUsedInInvestingActivities us-gaap true debit duration No definition available. false false false false false false false false false false false totallabel false 1 false true false false -80915000 -80915 false false false 2 false true false false -91334000 -91334 false false false xbrli:monetaryItemType monetary The net cash inflow (outflow) from investing activity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 true 94 INCREASE IN CASH AND CASH EQUIVALENTS 2 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease us-gaap true na duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 41482000 41482 false false false 2 false true false false 34535000 34535 false false false xbrli:monetaryItemType monetary The net change between the beginning and ending balance of cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 26 false 95 Cash and Cash Equivalents at Beginning of Year 2 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant No definition available. false false false false false false false false true false false periodstartlabel false 1 false true false false 5160000 5160 false false false 2 false true false false 3680000 3680 false false false xbrli:monetaryItemType monetary Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits should not be reported as cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 26 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8, 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 false 96 Cash and Cash Equivalents at End of Year 2 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant No definition available. false false false false false false false false false true false periodendlabel false 1 false true false false 46642000 46642 false false false 2 false true false false 38215000 38215 false false false xbrli:monetaryItemType monetary Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits should not be reported as cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 26 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8, 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 false 97 SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION 2 us-gaap_SupplementalCashFlowInformationAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 98 Income taxes paid 2 us-gaap_IncomeTaxesPaid us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 38713000 38713 false false false 2 false true false false 33861000 33861 false false false xbrli:monetaryItemType monetary The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 29 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 27 -Subparagraph f false 99 Interest paid 2 us-gaap_InterestPaid us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 21044000 21044 false false false 2 false true false false 23465000 23465 false false false xbrli:monetaryItemType monetary The amount of cash paid during the current period for interest owed on money borrowed; includes amount of interest capitalized Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 29 false 100 SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING ACTIVITIES 2 us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string Designated to encapsulate the entire footnote disclosure that gives information on the supplemental cash flow activities for noncash (or part noncash) transactions for the period. Noncash is defined as information about all investing and financing activities of an enterprise during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. false 101 Extinguishment of project debt financing 2 us-gaap_ExtinguishmentOfDebtAmount us-gaap true debit duration No definition available. false false false false false false false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false true false false 7375000 7375 false false false xbrli:monetaryItemType monetary Gross amount of debt extinguished. No authoritative reference available. false 102 Capital expenditures included in accounts payable and other accrued liabilities 2 us-gaap_CapitalExpendituresIncurredButNotYetPaid us-gaap true credit duration No definition available. false false false false false false false false false false false verboselabel false 1 true true false false 3206000 3206 false false false 2 true true false false 4822000 4822 false false false xbrli:monetaryItemType monetary Future cash outflow to pay for purchases of fixed assets that have occurred. No authoritative reference available. false 2 101 false Thousands UnKnown UnKnown false true