Washington Gas Light (WGLCP) 10-KT 4 Mar 19 2018 FY Annual report (with FYE transition) Financial data

Document and Entity Information

Document and Entity Information - USD ($)	3 Months Ended
	Dec. 31, 2018	Jan. 31, 2019	Jun. 30, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	Washington Gas Light Company
Entity Central Index Key	104,819
Document Type	10-KT
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Former Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Public Float			$ 0
Entity Common Stock, Shares Outstanding		46,479,536
Par Value Per Share	$ 1

Balance Sheet

Balance Sheet - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Property, Plant and Equipment
At original cost	$ 5,702,927	$ 5,613,137	$ 5,310,337
Accumulated depreciation and amortization	(1,513,590)	(1,495,683)	(1,422,622)
Net property, plant and equipment	4,189,337	4,117,454	3,887,715
Current Assets
Cash and cash equivalents	6,082	1	1
Receivables
Accounts receivable	292,871	165,257	190,740
Gas costs and other regulatory assets	6,020	5,054	21,705
Unbilled revenues	189,497	101,114	107,967
Allowance for doubtful accounts	(29,461)	(29,622)	(23,741)
Net receivables	458,927	241,803	296,671
Materials and supplies—principally at average cost	19,727	20,650	20,126
Storage gas	103,929	101,379	92,753
Prepaid taxes	27,193	17,732	23,350
Other prepayments	28,232	24,449	13,238
Receivables from associated companies	4,819	2,227	32,362
Derivatives	19,488	17,441	5,061
Other	20,347	20,347	102
Total current assets	688,744	446,029	483,664
Deferred Charges and Other Assets
Gas costs	141,636	83,222	90,136
Pension and other post-retirement benefits	86,493	56,983	138,573
Other	99,105	104,050	104,538
Prepaid post-retirement benefits	249,462	284,277	230,283
Derivatives	11,318	8,736	16,244
Other	50,490	49,331	3,561
Total deferred charges and other assets	638,504	586,599	583,335
Total Assets	5,516,585	5,150,082	4,954,714
Capitalization
Common shareholder’s equity	1,562,573	1,442,764	1,164,749
Washington Gas Light Company preferred stock	28,173	28,173	28,173
Long-term debt	1,035,033	1,084,933	1,134,461
Total capitalization	2,625,779	2,555,870	2,327,383
Current Liabilities
Current maturities of long-term debt	50,000	50,000	0
Notes payable and project financing	311,460	163,478	166,772
Accounts payable and other accrued liabilities	288,376	271,276	219,827
Wages payable	22,629	10,089	16,508
Accrued interest	14,504	4,000	3,967
Dividends declared	24,567	24,078	22,098
Customer deposits and advance payments	54,370	83,658	64,194
Gas costs and other regulatory liabilities	75,151	34,157	22,814
Accrued taxes	28,451	27,427	12,808
Payables to associated companies	95,228	21,548	94,844
Derivatives	20,295	14,838	30,263
Other	7,507	7,627	7,473
Total current liabilities	992,538	712,176	661,568
Deferred Credits
Unamortized investment tax credits	3,233	3,398	4,100
Deferred income taxes	454,248	409,807	888,385
Accrued pensions and benefits	156,210	118,204	179,814
Asset retirement obligations	300,769	298,202	291,871
Regulatory liabilities
Accrued asset removal costs	264,556	270,397	292,173
Other post-retirement benefits	121,345	159,152	134,181
Excess deferred taxes and other	431,913	443,665	9,403
Derivatives	116,847	104,165	112,299
Other	49,147	75,046	53,537
Total deferred credits	1,898,268	1,882,036	1,965,763
Commitments and Contingencies (Note 12)
Total Capitalization and Liabilities	$ 5,516,585	$ 5,150,082	$ 4,954,714

Statement of Income

Statement of Income - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	[1]	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
OPERATING REVENUES	$ 402,101					$ 377,470				$ 1,248,063	$ 1,166,968	$ 1,070,904
OPERATING EXPENSES
Utility cost of gas	156,641					124,745				407,043	297,856	271,975
Operation and maintenance	102,728					82,372				544,180	340,604	329,303
Depreciation and amortization	34,948					33,646				135,071	129,428	114,605
General taxes and other assessments	38,552					39,983				148,178	134,696	130,231
Total Operating Expenses	332,869					280,746				1,234,472	902,584	846,114
OPERATING INCOME	69,232	$ (225,462)		$ (6,649)	$ 148,978	96,724	$ (13,000)	$ 10,482	$ 164,876	13,591	264,384	224,790
Other income (expense) —net	3,494					1,029				(7,592)	(545)	1,434
Interest expense	15,706					14,973				58,504	52,207	41,444
INCOME (LOSS) BEFORE INCOME TAXES	57,020					82,780				(52,505)	211,632	184,780
INCOME TAX EXPENSE (BENEFIT)	7,847					24,854				(25,863)	79,840	71,666
NET INCOME (LOSS)	49,173	(181,153)		(11,499)	108,084	57,926	(15,608)	(1,671)	93,610	(26,642)	131,792	113,114
Dividends on preferred stock	330					330				1,320	1,320	1,320
NET INCOME (LOSS) APPLICABLE TO COMMON STOCK	$ 48,843	$ (181,483)		$ (11,829)	$ 107,754	$ 57,596	$ (15,938)	$ (2,001)	$ 93,280	$ (27,962)	$ 130,472	$ 111,794
[1]	During the quarter ended September 30, 2018, Washington Gas recorded $200.2 million of merger related costs due to the Merger with AltaGas.

Statement of Comprehensive Inco

Statement of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
NET INCOME (LOSS)	$ 49,173		$ (26,642)		$ 131,792		$ 113,114
Pension and other post-retirement benefit plans
Change in prior service (cost) credit	(226)	[1]	(675)	[1]	(767)	[1]	(891)
Change in actuarial net gain (loss)	(6,246)	[1]	6,324	[1]	6,232	[1]	(936)
Total pension and other post-retirement benefit plans	(6,472)		5,649		5,465		(1,827)
INCOME TAX EXPENSE (BENEFIT) RELATED TO OTHER COMPREHENSIVE INCOME (LOSS)	(1,675)		2,957		2,157		(709)
OTHER COMPREHENSIVE INCOME (LOSS)	(4,797)		2,692		3,308		(1,118)
COMPREHENSIVE INCOME (LOSS)	$ 44,376		$ (23,950)		$ 135,100		$ 111,996
[1]	These accumulated other comprehensive income (loss) components are included in the computation of net periodic benefit cost. Refer to Note 9—Pension and other post-retirement benefit plans for additional details.

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
OPERATING ACTIVITIES
NET INCOME (LOSS)	$ 49,173	$ (26,642)	$ 131,792	$ 113,114
ADJUSTMENTS TO RECONCILE NET INCOME TO NET CASH PROVIDED BY OPERATING ACTIVITIES
Depreciation and amortization	34,948	135,071	129,428	114,605
Amortization of:
Other regulatory assets and liabilities—net	1,859	6,917	6,422	1,909
Debt related costs	382	1,580	1,448	1,191
Deferred income taxes-net	8,012	(26,435)	77,586	123,482
Accrued/deferred pension and other post-retirement benefit cost	(330)	11,127	22,547	19,497
Compensation expense related to stock-based awards	1,353	19,067	16,153	11,452
Provision for doubtful accounts	5,940	20,224	14,484	10,945
Impairment loss	2,453	37,969	0	0
Unrealized (gain) loss on derivative contracts	4,200	(10,379)	(48,950)	(11,552)
Amortization of investment tax credits	(165)	(702)	(751)	(795)
Other non-cash charges (credits)—net	(453)	(2,450)	(1,592)	(197)
Changes in operating assets and liabilities (Note 17)	(201,840)	(43,050)	(141,238)	(143,526)
Net Cash (Used In) Provided by Operating Activities	(94,468)	122,297	207,329	240,125
FINANCING ACTIVITIES
Capital contributions from parent	100,000	402,728	0	0
Long-term debt issued	0	0	195,556	248,125
Long-term debt retired	(50,000)	0	0	(25,000)
Debt issuance costs	0	(366)	(661)	(333)
Notes payable issued (retired)—net	200,999	(27,998)	81,000	(47,000)
Project financing	0	53,018	9,314	38,468
Dividends on common stock and preferred stock	(24,078)	(88,908)	(87,118)	(83,116)
Other financing activities—net	0	(6,197)	(1,982)	(277)
Net Cash Provided by Financing Activities	226,921	332,277	196,109	130,867
INVESTING ACTIVITIES
Net proceeds from sale of assets	0	0	0	19,749
Capital expenditures (excluding AFUDC)	(126,013)	(392,830)	(403,438)	(390,741)
Insurance proceeds related to investing properties	0	3,238	0	0
Net Cash Used in Investing Activities	(126,013)	(389,592)	(403,438)	(370,992)
INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	6,440	64,982	0	0
Cash, Cash Equivalents, and Restricted Cash at Beginning of the Year	64,983	1	1	1
Cash, Cash equivalents and Restricted Cash at End of the Year	$ 71,423	$ 64,983	$ 1	$ 1

Consolidated Statements of Comm

Consolidated Statements of Common Shareholders Equity - USD ($) $ in Thousands		Total	Common Stock	Paid-In Capital	Retained Earnings		Accumulated Other Comprehensive Loss, Net of Taxes		Total	ASU 2016-09	ASU 2018-02
Beginning Balance, shares at Sep. 30, 2015			46,479,536
Common shareholders' equity, beginning balance at Sep. 30, 2015			$ 46,479	$ 483,677	$ 557,848		$ (6,712)		$ 1,081,292
Increase (Decrease) in Stockholders' Equity [Roll Forward]
NET INCOME (LOSS)		$ 113,114			113,114				113,114
OTHER COMPREHENSIVE INCOME (LOSS)		(1,118)					(1,118)		(1,118)
Stock-based compensation	[1]			(4,458)					(4,458)
Capital contributed by WGL Holdings		0
Dividends Abstract
Common Stock					(82,980)				(82,980)
Preferred Stock					(1,320)				(1,320)
Common shareholders' equity, ending balance at Sep. 30, 2016			$ 46,479	488,135	586,662		(7,830)		1,113,446
Ending Balance, shares at Sep. 30, 2016			46,479,536
Increase (Decrease) in Stockholders' Equity [Roll Forward]
NET INCOME (LOSS)		131,792			131,792				131,792
OTHER COMPREHENSIVE INCOME (LOSS)		3,308					3,308		3,308
Stock-based compensation	[1]			(3,966)					(3,966)
Capital contributed by WGL Holdings		0
Dividends Abstract
Common Stock					(86,443)				(86,443)
Preferred Stock					(1,320)				(1,320)
Common shareholders' equity, ending balance at Sep. 30, 2017		1,164,749	$ 46,479	492,101	630,691		(4,522)		1,164,749
Ending Balance, shares at Sep. 30, 2017			46,479,536
Increase (Decrease) in Stockholders' Equity [Roll Forward]
NET INCOME (LOSS)		(26,642)			(26,642)				(26,642)
OTHER COMPREHENSIVE INCOME (LOSS)		2,692					4,176		4,176
Stock-based compensation	[1]			(15,556)	(4,197)				(11,359)
Capital contributed by WGL Holdings		402,728		402,728					402,728
Dividends Abstract
Common Stock					(89,568)				(89,568)
Preferred Stock					(1,320)				(1,320)
Common shareholders' equity, ending balance at Sep. 30, 2018		1,442,764	$ 46,479	879,273	518,842		(1,830)		1,442,764
Ending Balance, shares at Sep. 30, 2018			46,479,536
Increase (Decrease) in Stockholders' Equity [Roll Forward]
ASU 2018-02 adoption impact					1,484	[2]	(1,484)	[2]			$ 1,500
Dividends Abstract
Retained Earnings (Accumulated Deficit)										$ (4,200)
NET INCOME (LOSS)		49,173							49,173
OTHER COMPREHENSIVE INCOME (LOSS)		(4,797)					(4,797)		(4,797)
Capital contributed by WGL Holdings		100,000		100,000					100,000
Common Stock					(24,237)				(24,237)
Preferred Stock					(330)				(330)
Common shareholders' equity, ending balance at Dec. 31, 2018		$ 1,562,573	$ 46,479	$ 979,273	$ 543,448		$ (6,627)		$ 1,562,573
Ending Balance, shares at Dec. 31, 2018			46,479,536
[1]	Stock-based compensation is based on the stock awards of WGL that are allocated to Washington Gas Light Company for its pro-rata share. We recorded $4.2 million commutative adjustments to retained earnings for the fiscal year 2018 due to the adoption of ASU 2016-09. We accelerated the vesting of stock-based awards upon the consummation of the Merger with AltaGas during the 4th quarter of fiscal year 2018, which reduced the paid-in capital. See Note 11—Stock-Based Compensation for a further discussion.
[2]	Amount related to the adoption of ASU 2018-02. Washington Gas reclassified a credit of $1.5 million from AOCI to retained earnings at September 30, 2018.

Accounting Policies

Accounting Policies	3 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Business Description and Accounting Policies [Text Block]	ACCOUNTING POLICIES Organization Washington Gas is an indirect, majority owned subsidiary of, among other entities, of AltaGas and WGL. On July 6, 2018 , the Merger was consummated between AltaGas, WGL, and the Merger Sub, with WGL surviving as an indirect wholly owned subsidiary of AltaGas. In connection with the Merger, WGL established the SPE for the purposes of owning the common stock of Washington Gas. The SPE is a wholly owned subsidiary of WGL. Except where the content clearly indicates otherwise, any reference in this report to “Washington Gas”,” “we,” “us”, “our” or the "Company” refers to Washington Gas Light Company. References to “WGL” refer to WGL Holdings, Inc. and all of its subsidiaries. Refer to Note 18— Merger with AltaGas, Ltd. , of the Notes to Financial Statements for a further discussion of the Merger Agreement. Nature of Operations Washington Gas is a public utility that sells and delivers natural gas to more than one million customers primarily in the District of Columbia and the surrounding metropolitan areas in Maryland and Virginia. Deliveries to firm residential and commercial customers accounted for 84% of the total therms delivered to customers by Washington Gas in the three months ended December 31, 2018 . Deliveries to interruptible customers accounted for 12% and deliveries to customers who use natural gas to generate electricity accounted for 4% . These amounts do not include deliveries related to Washington Gas’ asset optimization program discussed below. Hampshire is an affiliate that operates an underground natural gas storage facility that provides services exclusively to Washington Gas. Hampshire is regulated under a cost of service tariff by the FERC. Washington Gas provides certain shared services to its affiliates, in which it is reimbursed for the costs associated with those services. Basis of Presentation The Financial Statements of Washington Gas has been prepared in conformity with GAAP and under the rules of the Securities and Exchange Commission (SEC). The Merger with AltaGas was recorded using the acquisition method of accounting. Under SEC regulations, Washington Gas elected to not apply push down accounting to its stand alone financial statements. The acquisition adjustments were recorded by AltaGas. The information presented in this transition report on Form 10-K are presented solely for the registrant Washington Gas on a stand-alone basis. As a result of the Merger, there were no changes in accounting principles and practices or method of application that had a material effect on the financial results for the transition period ended December 31, 2018 and for the fiscal year ended September 30, 2018. Change of Fiscal Year End On December 28, 2018, our Board of Directors approved a change of our fiscal year from the period beginning on October 1 and ending on September 30 to the period beginning on January 1 and ending on December 31. This transition report on Form 10-K includes financial information for the three-month transition period from October 1, 2018 through December 31, 2018, or the transition period ended December 31, 2018. References in this report to fiscal year 2018, 2017 and 2016 refer to twelve-month periods ended in September 30 of each year. All amounts presented for the three months ended December 31, 2017 are unaudited. Subsequent to this transition report, our annual reports on Form 10-K will cover the calendar year from January 1 to December 31, with historical periods remaining unchanged. Use of Estimates in the Preparation of Financial Statements In accordance with GAAP, we make certain estimates and assumptions regarding: (i) reported assets and liabilities; (ii) disclosed contingent assets and liabilities at the date of the financial statements and (iii) reported revenues, revenues subject to refund, and expenses during the reporting period. Actual results could differ from those estimates. Property, Plant and Equipment Property, plant and equipment (comprised principally of utility plant) are stated at original cost, including labor, materials, taxes and overhead costs incurred during the construction period. The cost of utility plant of Washington Gas includes an allowance for funds used during construction (AFUDC) that is calculated under a formula prescribed by our regulators in Maryland and the District of Columbia. Washington Gas capitalizes AFUDC as a component of construction overhead. The rates for AFUDC for three months ended December 31, 2018 was 5.84% and for fiscal years September 30, 2018, 2017 and 2016 were 2.42% , 2.73% and 5.51% , respectively. Washington Gas charges maintenance and repairs directly to operating expenses. Washington Gas capitalizes betterments and renewal costs and calculates depreciation applicable to its utility gas plant in service primarily using a straight-line method over the estimated remaining life of the plant. The composite annual depreciation and amortization rate was 2.78% for the three months ended December 31, 2018, and 2.77% , 2.80% and 2.69% for fiscal years 2018 , 2017 and 2016 , respectively. In accordance with regulatory requirements, such rates include a component related to asset removal costs for Washington Gas. These asset removal costs are accrued through depreciation expense with a corresponding credit to “Regulatory liabilities—Accrued asset removal costs.” When Washington Gas retires depreciable utility plant and equipment, it charges the associated original costs to “Accumulated depreciation and amortization” and any related removal costs incurred are charged to “Regulatory liabilities—Accrued asset removal costs.” Washington Gas periodically reviews the adequacy of its depreciation rates by considering estimated remaining lives and other factors. For information about Asset Retirement Obligations (ARO’s), refer to the section entitled “Asset Retirement Obligations”. The following table represents the components of Washington Gas' Property, Plant and Equipment at original cost. Property, Plant and Equipment at Original Cost ($ In millions) December 31, September 30, 2018 2018 2017 Distribution, transmission and storage $ 4,888.4 85.7 % $ 4,766.5 84.9 % $ 4,502.6 84.8 % General, miscellaneous and intangibles 542.9 9.5 % 536.4 9.6 % 545.6 10.2 % Construction work in progress (CWIP) 271.6 4.8 % 310.2 5.5 % 262.1 5.0 % Total 5,702.9 100.0 % 5,613.1 100.0 % 5,310.3 100.0 % Impairment of Long-Lived Assets Management regularly reviews property and equipment and other long-lived assets for possible impairment whenever events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. For our properties and equipment, the indicators of potential impairment may include a deteriorating business or legal climate, a significant adverse change in asset condition, specific regulatory disallowance, advances in technology or plans to dispose of an asset significantly before the end of its useful life, among others. Management performs the recoverability test whenever the indicators show a possible impairment. The amount used to test recoverability is determined based on an estimate of undiscounted cash flows, and measurement of an impairment loss is determined based on the fair value of the assets. The determination of fair value requires management to make assumptions about future cash inflows and outflows over the life of an asset. Any changes to the assumptions used for the future cash flow could result in revisions to the evaluation of the recoverability of the long-lived assets and the recognition of an impairment loss in the Consolidated Financial Statements. During the fiscal year ended September 30, 2018, Washington Gas recorded a $ 38.0 million impairment to Property, Plant and Equipment in connection with an agreement ancillary to the merger proceeding not to seek recovery of certain costs incurred under the Formal Case 1027 mechanical coupling program. As part of the program, Washington Gas agreed to encapsulate or replace vintage mechanical couplings mechanically coupled pipe to mitigate potential gas leaks. During the three months ended December 31, 2018, and fiscal year ended September 30, 2017 and 2016, Washington Gas did not record any impairments related to our long-lived assets. Refer to Note 14 — Fair Value Measurements and Note 18 — Merger with AltaGas, Ltd. , of the Notes to Consolidated Financial Statements for further discussion of these assets. Operating Leases We have classified the leases of multiple office locations as operating leases. We amortize as rent expense the total of all scheduled lease payments (including lease payment escalations) and tenant allowances on a straight-line basis over the term of the leases. For this purpose, the lease term begins on the date when the lessor commenced constructing the leasehold improvements which allowed us to occupy the respective locations. Leasehold improvement costs are classified as “Property, Plant and Equipment” on the Balance Sheets, and are being amortized to depreciation and amortization expense on a straight-line basis over the non-cancelable period of the leases. Refer to Note 12— Commitments and Contingencies for financial data for all of our operating leases. Cash and Cash Equivalents We consider all investments with original maturities of three months or less to be cash equivalents Restricted Cash and Cash Equivalents Restricted cash and cash equivalents represent funds that are restricted to satisfy designated liabilities. Restricted cash and cash equivalents available to satisfy designated current liabilities are classified as current assets. Restricted cash and cash equivalents expected to satisfy non-current liabilities are classified as non-current assets. Pursuant to the Merger Agreement with AltaGas, we funded rabbi trusts of retirement benefits for executives and select management employees and deferred compensation benefits for outside directors in the fiscal ended September 30, 2018. As of December 31 and September 30, 2018, the rabbi trust funds are invested in money market funds which are considered as cash equivalents. The rabbi trust funds that are used for the settlement of benefit plans in long-term liabilities are classified in “Deferred charges and other assets-other”. The rabbi trust funds to settle benefit plans in current liabilities are classified in “Current Assets-Other” on Washington Gas’ balance sheet. We did not have any restricted cash and cash equivalents as of September 30, 2017 or September 30, 2016. Refer to Note 9- Pension and Other Post-Retirement Benefits for a further discussion of the rabbi trusts and Note 17- Supplemental Cash Flow Information for a further discussion of restricted cash and cash equivalents. Allowance for Doubtful Accounts The allowance for doubtful accounts reflects Washington Gas' estimate of losses inherent in its account receivable balances. Washington Gas estimates its bad debt expense based on current sales and establishes the allowance. Periodically, Washington Gas evaluates the reasonableness of the allowance utilizing a variety of factors including the length of time receivables are past due, the financial health of its customers, unusual macroeconomic conditions, and historical payment and collection experience. If the financial condition of its customers deteriorates or other circumstances occur that impact the customers’ ability or desire to make payments, Washington Gas considers these factors in its evaluation of the adequacy of the allowance. Accounts are written off to the allowance when collection efforts are complete and future recovery is unlikely. Revenue and Cost of Gas Recognition Revenues. The Utility recognizes revenue from contracts with customers to depict the transfer of goods or services to customers at an amount it expects to be entitled to in exchange for those goods or services. Generally, goods or services are transferred to our customer when the natural gas is delivered. Washington Gas reads meters and bills customers on a 19 -day monthly cycle basis. The billing cycles for customers do not coincide with the accounting periods used for financial reporting purposes; therefore, Washington Gas accrues unbilled revenues for gas delivered, but not yet billed, at the end of each accounting period. Refer to Note 2 - Revenue from Contracts with Customers for further discussion of the Utility’s revenue from contracts with customers. Alternative Revenue Programs. Certain ratemaking mechanisms of Washington Gas qualify as alternative revenue programs in accordance with ASC Topic 980, Regulated Operations, if the program (i) is established by an order from the regulatory commissions and allows for automatic adjustment of future rates, (ii) the additional revenues (above those amounts currently reflected in base rates) that are objectively determinable and probable of recovery, and (iii) allow for the collection of the additional revenues within 24 months following the end of the period in which they were recognized. The Company has determined that its RNA, WNA and CRA billing adjustment mechanisms and accelerated pipe replacement programs are alternative revenue programs. Alternative revenue program revenues represent the initial recognition of revenue related to these programs. When amounts are billed and collected from customers through rates, the amounts are recorded as a recovery of the associated regulatory asset or liability. Cost of Gas. Washington Gas’ jurisdictional tariffs contain mechanisms that provide for the recovery of the cost of gas incurred on behalf of firm customers, including related pipeline transportation and storage capacity charges. Under these mechanisms, Washington Gas periodically adjusts its firm customers’ rates to reflect increases and decreases in these costs. Under or over-collections of gas costs in the current cycle are charged or credited to deferred charges or credits on the balance sheet as non-current regulatory assets or liabilities. Amounts deferred at the end of the cycle, August 31 of each year, are fully reconciled and transferred to current assets or liabilities under the balance sheet captions “Gas costs and other regulatory assets” and “Gas costs and other regulatory liabilities.” These balances are recovered or refunded to customers over the subsequent 12 month period. Revenue Taxes. Revenue taxes such as gross receipts taxes, Public Service Commission (PSC) fees, franchise fees and energy taxes are reported gross in operating revenues. During the three months ended December 31, 2018, $24.2 million was recorded to operating revenues. During fiscal years ended September 30, 2018, 2017 and 2016 , $ 82.5 million , $75.1 million , and $73.0 million , respectively, were recorded to operating revenues. Transportation Gas Imbalance. Interruptible shippers and third-party marketer shippers transport gas to Washington Gas’ distribution system as part of the unbundled services offered. The delivered volumes of gas from third-party shippers into Washington Gas’ distribution system rarely equal the volumes billed to third-party marketer customers, resulting in transportation gas imbalances. These imbalances are usually short-term in duration, and Washington Gas monitors the activity and regularly notifies the shippers when their accounts have an imbalance. In accordance with regulatory treatment, Washington Gas does not record a receivable from or liability to third-party marketers associated with gas volumes related to these transportation imbalances but, rather, reflects the financial impact as a regulatory asset or liability related to its gas cost adjustment mechanism, thereby eliminating any profit or loss that would occur as a result of the imbalance. The regulatory treatment combines the imbalance for all marketers, including our affiliate WGL Energy Services, into a single “net” adjustment to the regulatory asset or liability. Refer to Note 15— Related Party Transactions for further discussion of the accounting for these imbalance transactions. Asset Optimization Program. Washington Gas optimizes the value of its long-term natural gas transportation and storage capacity resources by entering into physical and financial transactions in the form of forwards, futures and option contracts for periods when these resources are not being used to physically serve utility customers. Refer to “Derivative Activities” below for further discussion of the accounting for derivative transactions entered into under this program. Regulatory sharing mechanisms in all three jurisdictions allow the profit from these transactions to be shared between Washington Gas’ customers and shareholder. All unrealized fair value gains and losses, and margins generated from the physical and financial settlement of these asset optimization contracts are recorded in "Utility cost of gas" on the income statement or, in the case of amounts to be shared with rate payers, regulatory assets/liabilities on the balance sheet. Storage Gas Valuation Methods Prior to September 30, 2017, Washington Gas accounted for storage gas inventories using the first-in, first-out method under which the oldest inventory items were recorded as being sold first. Starting in October 1, 2017, Washington Gas implemented a voluntary change in the application of an accounting principle with respect to accounting for natural gas, propane, and odorant inventories. Washington Gas now applies the average cost methodology under which the cost of units carried in inventory is based on the weighted average cost per unit of inventory. Washington Gas implemented the change in accounting principle on a prospective basis in accordance with ASC Topic 980, which permits regulated entities to implement changes for financial reporting purposes in the same way those changes are implemented for regulatory reporting purposes when the change impacts allowable costs. On October 1, 2017, WGL adopted ASU 2015-11, Inventory (Topic 330) - Simplifying the Measurement of Inventory. This standard modified the previous calculation for valuing inventory. As a result of the new standard, beginning October 1, 2017, our inventory balances are stated at the lower of cost or net realizable value. Prior to October 1, 2017, our inventory balances were stated at the lower of cost or market. Interim period inventory losses attributable to lower of cost or net realizable value adjustments may be reversed if the net realizable value of the inventory is recovered by the end of the same fiscal year. Washington Gas did not record a lower-of-cost or net realizable value adjustment to net income for the three months ended December 31, 2018 and fiscal year ended September 30, 2018 or a lower-of-cost or market adjustment to net income for the fiscal year ended September 30, 2017 and 2016. Derivative Activities Washington Gas enters into both physical and financial derivative contracts for the purchase and sale of natural gas that are subject to mark-to-market accounting. Changes in the fair value of derivative instruments which are recoverable or refundable to customers when they settle are subject to ASC Topic 980 and are recorded as regulatory assets or liabilities while changes in the fair value of derivative instruments not affected by rate regulation are reflected in earnings. As part of its asset optimization program, Washington Gas enters into derivative contracts related to the sale and purchase of natural gas at a future price with the primary objective of securing operating margins that Washington Gas expects to ultimately realize. The fair value changes of derivatives used under this program may cause significant period-to-period volatility in earnings for the portion of net profits retained for shareholders; however, this earnings volatility will not change the realized margins that Washington Gas expects to earn. In accordance with ASC Topic 815, all financially and physically settled contracts under our asset optimization program are reported on a net basis in the statements of income in “Utility cost of gas”. From time to time, Washington Gas also utilizes derivative instruments that are designed to minimize the risk of interest-rate volatility associated with planned issuances of long-term debt. Gains or losses associated with these derivative transactions are deferred as regulatory assets or liabilities and amortized to interest expense in accordance with regulatory accounting requirements. Refer to Note 13— Derivatives for further discussion of our derivative activities. Income Taxes We recognize deferred income tax assets and liabilities for all temporary differences between the financial statement basis and the tax basis of assets and liabilities computed on a separate company basis. Our deferred income taxes include those that are currently excluded for ratemaking purposes of Washington Gas. Regulatory assets or liabilities, corresponding to such additional deferred income tax assets or liabilities, may be recorded to the extent recoverable from or payable to customers through the ratemaking process in future periods. Refer to Note 3— Regulated Operations for Washington Gas’ regulatory assets and liabilities associated with income taxes due from and due to customers. Amounts applicable to income taxes due from and due to customers primarily represent differences between the financial statement basis and tax basis of net utility plant in service. Refer to Note 8— Income Taxes which provides detailed financial information related to our income taxes. Stock-Based Compensation We account for stock-based compensation expense in accordance with ASC Topic 718, Compensation-Stock Compensation, and all outstanding awards as of December 31, 2018 are liability-classified share-based awards. We recognize stock-based compensation expense based on their fair value at the end of each reporting period. In addition, certain awards are accounted for under ASC Topic 710, Compensation - General, because they do not meet the definition of a stock-based award under ASC Topic 718. Compensation expense is recognized based on the probable outcome of the award at the end of each reporting period. We estimate forfeitures over the requisite service period when recognizing compensation expense; these estimates are periodically adjusted to the extent to which actual forfeitures differ from such estimates. Refer to Note 10- Stock-Based Compensation for further discussion of the accounting for our stock-based compensation plans. Asset Retirement Obligations Washington Gas accounts for its AROs in accordance with ASC Subtopic 410-20, Asset Retirement and Environmental Obligations—Asset Retirement Obligations. Our AROs include the costs to cut, purge and cap Washington Gas' distribution and transmission system and plug storage wells upon their retirement. These standards require recording the estimated retirement cost over the life of the related asset by depreciating the present value of the retirement obligation, measured at the time of the asset’s acquisition, and accreting the liability until it is settled. There are timing differences between the ARO-related accretion and depreciation amounts being recorded pursuant to GAAP and the recognition of depreciation expense for legal asset removal costs that we are currently recovering in rates. These timing differences are recorded as a reduction to “Regulatory liabilities—Accrued asset removal costs” in accordance with ASC Topic 980. We do not have any assets that are legally restricted related to the settlement of asset retirement obligations. Changes in Asset Retirement Obligations (In millions) December 31, September 30, 2018 2018 2017 Asset retirement obligations at beginning of year $ 305.5 $ 298.9 $ 206.6 Liabilities incurred in the period — 1.4 2.0 Revaluation of asset retirement obligation — — 89.5 Liabilities settled in the period — (7.3 ) (7.2 ) Accretion expense 2.6 12.5 8.0 Asset retirement obligations at the end of the year (a) $ 308.1 $ 305.5 $ 298.9 (a)Includes short-term asset retirement obligations of $7.3 million , $7.3 million and $7.1 million for three months ended December 31, 2018, and fiscal years ended September 30, 2018 and September 30, 2017 , respectively. Accounting Standards Adopted in the Transition Period and Other Newly Issued Accounting Standards The following tables represent accounting standards adopted by Washington Gas during the three-month transition period ended December 31, 2018, and other newly issued accounting standards that will be adopted by Washington Gas in the future. ACCOUNTING STANDARDS ADOPTED IN THREE MONTHS TRANSITION PEPRIOD Standard Description Date of adoption Effect on the financial statements or other significant matters ASU 2014-09, Revenue from Contracts with Customers (Topic 606), including subsequent ASUs clarifying the guidance. ASU 2014-09 establishes a comprehensive revenue recognition model clarifying the method used to determine the timing and requirements for revenue recognition from contracts with customers. The disclosure requirements under the new standard will enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. October 1, 2018 Washington Gas adopted the new guidance using the modified retrospective approach, which does not require prior year results to be restated. Adoption of this standard did not have a material change in the timing or pattern of revenue recognition and a cumulative-effect adjustment was not recorded at October 1, 2018. The significant impact of adopting this standard is the additional disclosures around the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. For the new disclosures, see the Revenue and Cost Recognition discussion above and Note 2 - Revenue from Contracts with Customers . ASU 2016-01, Financial Instruments (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities including subsequent ASUs clarifying the guidance. This guidance applies to the recognition and measurement of financial assets and liabilities. The standard requires equity investments, except those accounted for under the equity method of accounting or consolidated, to be measured at fair value with changes in the fair value recognized in net income. The standard also amends presentation requirements related to certain changes in the fair value of a liability and eliminates certain disclosure requirements of significant assumptions for financial instruments measured at amortized cost on the balance sheet. October 1, 2018 The adoption of this standard and related amendments did not have a material impact on our consolidated financial statements or on our disclosures. 2016-16, Income Taxes (Topic 740): Intra-entity Transfers of Assets Other Than Inventory This standard revised the accounting for income taxes by requiring an entity to recognize the current and deferred income tax consequences of an intra-entity asset transfer (other than inventory) when the transfer occurs. The standard should be applied on modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. October 1, 2018 The adoption of this standard and related amendments did not have a material effect on the financial statements. ASU No. 2017-01, (Topic 805): Business Combinations - Clarifying the Definition of a Business This standard changed the definition of a business to assist entities with the evaluation of whether a transaction should be accounted for as an acquisition (or disposal) of assets or a business. The standard should be applied on a prospective basis to transactions that occur on or after the effective date. October 1, 2018 Washington Gas will apply the amendments in this standard on a prospective basis and did not have an impact on the financial statements. ASU 2017-05, Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets The amendments in this ASU clarified the scope of ASC 610-20, as well as, the accounting for partial sales of nonfinancial assets. The standard can be applied either on a retrospective basis or on a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. October 1, 2018 The adoption of this standard did not have an impact on the financial statements. ASU 2017-07, Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost This standard requires entities to report the service cost component in the same financial statement line item as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are to be presented separately from service cost and outside of operating income. In addition, only the service cost component of net benefit cost is eligible for capitalization. Changes to the presentation of service costs and other components of net benefit cost should be applied retrospectively. Changes in capitalization practices should be implemented prospectively. October 1, 2018 We have concluded our evaluation of the interaction of this standard with the various regulatory provisions concerning pensions and post-retirement benefit costs. For the fiscal years ended September 30, 2018, 2017 and 2016, we recorded a reclassification of $11.3 million, $3.9 million and $3.6 million, respectively, of net periodic benefit income from operation and maintenance expenses to other income in the Statement of Income. The change in capitalization of retirement benefits have been implemented on a prospective basis and did not have a material impact on the financial statements. ASU 2017-09, Compensation-Stock Compensation (Topic 718): Scope of Modification Accounting This standard provided guidance on the types of changes to the terms or conditions of a shared-based payment arrangement should apply modification accounting. The amendments should be applied on a prospective basis to awards modified on or after the effective date. October 1, 2018 The guidance in this standard was applied on a prospective basis and did not have an impact on the financial statements. ASU 2018-08, Not-for-Profit Entities (Topic 958)-Clarifying the Scope and the Accounting Guidance for Contributions Received and Contributions Made This standard provides clarification to assist entities in evaluating whether transactions should be accounted for as a contribution (nonreciprocal) or as an exchange (reciprocal) subject to other accounting guidance. The amendments should be applied on a modified prospective basis, however; retrospective application is permitted. October 1, 2018 The guidance in this standard did not have an impact on the financial statements. OTHER NEWLY ISSUED ACCOUNTING STANDARDS Standard Description Required date of adoption Effect on the financial statements or other significant matters ASU 2016-02, Leases (Topic 842), ASU 2018-01, Land Easement Practical Expedient for Transition to Topic 842, and ASU 2018-11, Targeted Improvements, including other subsequent ASUs clarifying the guidance ASU 2016-02 requires recognition of a right-to-use asset and lease liability by lessees on the statement of financial position and disclosure of key information about leasing arrangements. Lessor accounting remains substantially unchanged but the standard modifies what qualifies as a sales-type and direct financing lease and eliminated real-estate specific provisions. January 1, 2019 Washington Gas is in the final stages of evaluating the impact of adopting ASC Topic 842. Washington Gas will utilize the transition practical expedients which allow entities to not have to reassess whether an arrangement contains a lease and the lease classification under the provisions of ASC Topic 842, land easements, and not separating out the lease and non-lease components for certain classes of assets. Washington Gas has also elected to present prior comparative information under ASC 840. For its lessee leases with terms longer than 12 months, Washington Gas will be recording an increase to long-term assets (net of any lease incentives and prepaid or deferred rent balances) and an increase to noncurrent liabilities net of the current portion to be recorded in current liabilities.

Revenue from Contracts With Cus

Revenue from Contracts With Customers	3 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	REVENUE FROM CONTRACTS WITH CUSTOMERS As described in Note 1, the Company adopted ASU 2014-09, Revenue from Contracts with Customers (ASC 606) and subsequent ASUs clarifying the guidance on October 1, 2018, using the modified retrospective method of adoption. Under this approach, prior year results are not required to be restated. Adoption of this standard did not change the timing or pattern of revenue recognition and a cumulative-effect adjustment was not recorded at October 1, 2018. As a result, comparative disclosures for operating results for the three-month period ended December 31, 2018 are not applicable because revenue recognition did not materially change as a result of implementing the new standard. The significant impact of adopting this standard are the additional disclosures around the nature, and uncertainty of revenue and cash flows arising from contracts with customers which are included in Note 1 - Accounting Policies and below. Washington Gas sells natural gas and distribution services to residential, commercial, industrial and governmental customers through regulated tariff rates approve by regulatory commissions in the jurisdictions where Washington Gas operates. Customers are billed monthly based on regular meter readings. Customer billings are based on two main components: (i) a fixed service fee and (ii) a variable fee based on usage. Revenue is recognized over time as the natural gas is delivered or as the service has been performed. As meter readings are performed on a cycle basis, Washington Gas recognizes accrued revenue for any services rendered to its customers but not billed at month-end. The tariff sales are generally considered daily or “at-will” contracts as customers may cancel their service at any time, and revenue generally represents the amount the Utility is entitled to invoice. There are certain contracts that have terms of one year or longer. For these contracts, revenue is recognized based on the amount the Utility is entitled to bill the customer. Customers have the choice to purchase natural gas from competitive service providers. The Utility charges the competitive service providers balancing fees to manage the natural gas transportation imbalances. Where regulations require, the Utility issues customers a consolidated bill to include the natural gas supplied by the competitive service providers and distribution of natural gas. Washington Gas recognizes revenue only for distribution services that the Utility has provided to the customer, and the balancing fees for the services provided to the competitive service provider. We disaggregate revenue by type of service. The following table disaggregates revenue for the period ended December 31, 2018: Disaggregated Revenue by Type of Service (In millions) Three Months Ended December 31, 2018 Revenue from contracts with customers Gas and transportation sales Gas sold and delivered $ 303.2 Gas delivered for others 74.3 Other 12.5 Other revenues 1.5 Total revenue from contracts with customers $ 391.5 Other sources of revenue Revenue from alternative revenue programs (a) $ 9.1 Leasing revenue (b) 0.2 Other 1.3 Total revenue from other sources 10.6 Total Operating Revenue $ 402.1 (a) The company has determined that the Utility’s RNA, WNA and CRA billing adjustment mechanisms and accelerated pipe replacement programs are alternative revenue programs and accounted for under ASC Topic 980. (b) Revenue generated from Washington Gas lessor operating leases accounted for under ASC Topic 840, Leases. Washington Gas accrues unbilled revenues for gas delivered, but not yet billed at the end of each accounting period due to our customer billing cycles. “Unbilled revenues” represent performance obligations that have been satisfied and Washington Gas has an unconditional right to payment, except for contract assets related to the Washington Gas’ area-wide contract which requires project acceptance by government for the right to payment to occur. For the contract asset amounts reported in unbilled receivables, see Project Financing in Note 5- Short-Term Debt . W ashington Gas did not have any contract liabilities at December 31, 2018. The Company does not have transaction price amounts allocated to future performance obligations. The Company applies the practical expedient available under ASC Topic 606 and does not disclose information about the remaining performance obligations for (i) contracts with an original expected length of one year or less, (ii) contracts for which revenue is recognized at the amount to which the Company has the right to invoice for performance completed, and (iii) contracts with variable consideration that is allocated entirely to a wholly unsatisfied performance obligation or to a wholly unsatisfied promise to transfer a distinct good or service that forms part of a single performance obligation.

Regulated Operations

Regulated Operations	3 Months Ended
	Dec. 31, 2018
Regulated Operations [Abstract]
Regulated Operations	REGULATED OPERATIONS Washington Gas accounts for its regulated operations in accordance with ASC Topic 980. This standard includes accounting principles for companies whose rates are determined by independent third-party regulators. When setting rates, regulators may require us to record expense in different periods than may be appropriate for unregulated enterprises. When this occurs, Washington Gas defers the associated costs as assets (regulatory assets) on its balance sheet and records them as expenses on its income statement as it collects the revenues designed to recover these costs through customers’ rates. Further, regulators can also impose liabilities upon a company for gains previously realized or for amounts previously collected from customers for expenses expected to be incurred in the future (regulatory liabilities). When Washington Gas files a request with certain regulatory commissions to modify customers’ rates, it may be permitted to charge customers new rates, subject to refund, until the regulatory commission renders a final decision on the amount of the authorized change in rates. During this interim period, Washington Gas records a provision for a rate refund regulatory liability based on the difference between the amount it collects in rates and the amount it expects to recover from a final regulatory decision. Similarly, Washington Gas periodically records provisions for rate refunds related to other transactions. Actual results for these regulatory contingencies are often difficult to predict and could differ significantly from the estimates reflected in the financial statements. Refer to Note 12— Commitments and Contingencies for further discussion of regulatory matters and related contingencies. At December 31, 2018 , September 30, 2018 and September 30, 2017 , we recorded the following regulatory assets and liabilities on our balance sheets. These assets and liabilities will be recognized as revenues or expenses in future periods as they are reflected in customers’ rates. Regulatory Assets and Liabilities (In millions) Regulatory Assets Regulatory Liabilities Three Months Ended December 31, Fiscal Year Ended September 30, Three Months Ended December 31, Fiscal Year Ended September 30, 2018 2018 2017 2018 2018 2017 Current: Gas costs due from/to customers (a) $ 5.6 $ 4.4 $ 0.2 $ 46.9 $ 9.0 $ 10.6 Interruptible sharing (a) 0.4 — 2.4 1.7 1.5 0.7 Revenue normalization mechanisms for Maryland and Virginia (a) — — 11.7 3.6 3.6 1.4 Accelerated replacement recovery mechanisms (l) — 0.6 7.4 3.8 1.9 1.1 Rates subject to refund (c) — — — — — 9.0 Tax Cuts and Jobs Act rate refunds (d) — — — 19.2 18.1 — Total current $ 6.0 $ 5.0 $ 21.7 $ 75.2 $ 34.1 $ 22.8 Deferred: Accrued asset removal costs (m) $ — $ — $ — $ 264.6 $ 270.4 $ 292.2 Deferred gas costs (a)(b) 141.6 83.2 90.1 — — — Pension and other post-retirement benefits Deferred pension costs—trackers (e) 5.7 9.1 19.8 — — — ASC Topic 715 unrecognized costs/income (a)(f) Pensions 80.8 47.9 118.8 — — — Other post-retirement benefits — — — 121.3 159.2 134.2 Total pension and other post-retirement benefits 86.5 57.0 138.6 121.3 159.2 134.2 Other: Income tax-related amounts due from/to customers (g) 41.6 42.6 37.9 427.2 439.1 3.2 Losses/gains on issuance and extinguishments of debt and interest-rate derivative instruments (a)(h) 15.0 15.3 16.4 1.3 1.3 1.4 Rights-of-way fees (a) — — — 2.5 1.9 0.7 Business process outsourcing and related costs (a) 3.2 6.2 8.2 — — — Non-retirement employee benefits (a)(i) 15.6 16.5 17.8 — — — Deferred distribution integrity management (a)(j) 5.4 5.8 7.7 — — — Recoverable portion of abandoned liquid natural gas facility (a) 2.7 2.7 3.1 — — — Environmental response costs (a)(k) 5.8 5.0 2.5 — — — Energy efficiency program-Maryland (n) 3.4 4.5 5.3 — — — Other regulatory expenses (o) 6.4 5.5 5.6 0.9 1.4 4.1 Total other $ 99.1 $ 104.1 $ 104.5 $ 431.9 $ 443.7 $ 9.4 Total deferred $ 327.2 $ 244.3 $ 333.2 $ 817.8 $ 873.3 $ 435.8 Total $ 333.2 $ 249.3 $ 354.9 $ 893.0 $ 907.4 $ 458.6 (a) Washington Gas does not earn its overall rate of return on these assets. Washington Gas is allowed to recover and required to pay, using short-term interest rates, the carrying costs related to billed gas costs due from and to its customers in the District of Columbia and Virginia jurisdictions. (b) Includes fair value of derivatives, which are not included in customer bills until settled. (c) Represents provision established for refunds to customers when the substitution of final rates resulted in an amount greater than the amount collected during the interim period related to the 2016 Virginia Rate Case. (d) Represents amounts accrued for future refunds due to the Tax Cuts and Jobs Act of 2017. For a further discussion, see Rates and Regulatory Matters section of Management's Discussion Analysis and Note 8-Income Taxes in the Notes to Consolidated Financial Statements. (e) Relates to the District of Columbia jurisdiction. (f) Refer to Note 9-Pension and Other Post-Retirement Benefit Plans for a further discussion of these amounts. (g) This balance represents amounts due from customers for deferred tax liabilities related to tax benefits on deduction flowed directly to customers prior to the adoption of income tax normalization for ratemaking purposes and to tax rate changes including the latest reduction as a result of the Tax Act. (h) The losses or gains on the issuance and extinguishment of debt and interest-rate derivative instruments include unamortized balances from transactions executed in prior fiscal years. These transactions create gains and losses that are amortized over the remaining life of the debt as prescribed by regulatory accounting requirements. (i) Represents the timing difference between the recognition of workers compensation and short-term disability costs in accordance with generally accepted accounting principles and the way these costs are recovered through rates. (j) This balance represents amounts for deferred expenditures associated with Washington Gas’ Distribution Integrity Management Program (DIMP) in Virginia. (k) This balance represents allowed environmental remediation expenditures at Washington Gas sites to be recovered through rates for Maryland and the District of Columbia. The recovery period is over several years. (l) Balance represents amounts for deferred over or under collections of surcharges associated with Washington Gas' accelerated pipeline recovery programs in the District of Columbia, Maryland and Virginia. (m) Refer to Note 1-Accounting Policies for a further discussion of these amounts. (n) Balance represents amounts for deferred credits associated with Washington Gas' participation in the energy conservation and efficiency program EmPower in Maryland. (o) Balance primarily relates to the District of Columbia jurisdiction. As required by ASC Topic 980, Washington Gas monitors its regulatory and competitive environment to determine whether the recovery of its regulatory assets remains probable. If Washington Gas were to determine that recovery of these assets is no longer probable, it would write off the assets against earnings. We have determined that ASC Topic 980 continues to apply to our regulated operations. During the three months ended December 31, 2018, Washington Gas recorded a $2.5 million write down to regulatory asset associated with BPO 2.0 cost, which was disallowed to recovery as the result of the MD Rate Case.

Accounts Payable and Other Accr

Accounts Payable and Other Accrued Liabilities	3 Months Ended
	Dec. 31, 2018
Accounts Payable and Accrued Liabilities [Abstract]
Accounts Payable and Other Accrued Liabilities	ACCOUNTS PAYABLE AND OTHER ACCRUED LIABILITIES The table below provides details for the amounts included in “Accounts payable and other accrued liabilities” on the balance sheets. December 31, September 30, (In millions) 2018 2018 2017 Accounts payable—trade $ 228.9 $ 187.0 $ 174.9 Employee benefits and payroll accruals 28.0 32.9 32.4 Other accrued liabilities 31.5 51.4 12.5 Total $ 288.4 $ 271.3 $ 219.8

Short-Term Debt

Short-Term Debt	3 Months Ended
	Dec. 31, 2018
Short-term Debt [Abstract]
Short-Term Debt	SHORT-TERM DEBT Washington Gas satisfies the short-term financing requirements through the sale of commercial paper, financing arrangements with third-party lenders, or through bank borrowings. Due to the seasonal nature of our operations, short-term financing requirements can vary significantly during the year. Revolving credit agreements are maintained to support outstanding commercial paper and to permit short-term borrowing flexibility. The policy of Washington Gas is to maintain bank credit facilities in amounts equal to or greater than the expected maximum commercial paper position. The following is a summary of committed credit available at December 31, 2018 , September 30, 2018 and September 30, 2017 . Committed Credit Available ($ in millions) December 31, 2018 September 30, 2018 September 30, 2017 Committed credit agreements Unsecured revolving credit facility, expires December 19, 2019 (a) $350.0 $350.0 $350.0 Less: Commercial Paper (296.0) (95.0) (123.0) Net committed credit available $54.0 $255.0 $227.0 Weighted average interest rate 2.93% 2.42% 1.22% (a) Washington Gas has the right to request extensions with the banks’ approval. Washington Gas’ revolving credit facility permits it to borrow an additional $100 million , with the banks’ approval, for a total of $450 million . At December 31, 2018 , September 30, 2018 and September 30, 2017 , there were no outstanding bank loans from Washington Gas’ revolving credit facilities. Under the terms of the credit agreements, the ratio of financial indebtedness to total capitalization may not exceed 0.65 to 1.0 ( 65.0% ). At December 31, 2018 , Washington Gas' ratios of consolidated financial indebtedness to consolidated total capitalization was 47% . In addition, Washington Gas is required to inform lenders of changes in corporate existence, financial conditions, litigation and environmental warranties that might have a material adverse effect. Failure to inform the lenders’ agent of these material changes might constitute default under the agreements. Another potential default may be deemed to exist if Washington Gas were to fail to pay principal or interest when due on any other indebtedness. Such defaults, if not remedied, could lead to suspension of further loans and/or acceleration in which obligations become immediately due and payable. At December 31, 2018 , Washington Gas was in compliance with all of the covenants under their revolving credit facilities. PROJECT FINANCING Washington Gas previously obtained third-party project financing on behalf of the federal government to provide funds during the construction of certain energy management services projects entered into under Washington Gas' area-wide contract. The construction work is performed by WGL Energy Systems on behalf of Washington Gas. As the financing entity funds the project, Washington Gas establishes a payable to the financing entity and transfers the funds to WGL Energy Systems. As work is performed, Washington Gas establishes a receivable representing the government's obligation to remit principal and interest. The financing obligation in “Notes payable and project financing” and contract assets in “Unbilled revenues” are typically equal to each other at the end of the construction period, but there could be timing differences in the recognition during the construction period. When these projects are formally “accepted” by the government and deemed complete, Washington Gas assigns the ownership of the receivable to the financing entity in satisfaction of the obligation to the financing entity and removes both the receivable and the obligation related to the financing from its financial statements. If project acceptance does not occur by a specified date, the lender may require Washington Gas to make interim interest payments or repurchase the contract payments plus a termination fee. In Ma rch 2016, the SCC of VA denied Washington Gas' further participation in the third-party financing arrangement but allowed existing debt arrangements to remain intact until the related obligations were satisfied. As a result, WGL Energy Systems entered into an agreement to obtain third-party financing and receive funds directly from the third-party lender during the construction period associated with the related energy management service projects. As a result, Washington Gas is no longer liable under future third-party financing arrangements. Washington Gas continues to record a receivable representing the governments obligation and records an account payable to associated company to WGL Energy Systems for the construction work performed for the same amount. In October 2018, WGL Energy Systems repaid $53.0 million drawn by Washington Gas from a third-party lender for a specific project that the lender demanded repayment for due to delays in achieving final acceptance from the federal government agency customer. The $ 53.0 million was included in "Payables to associated companies" on Washington Gas' balance sheet as of December 31, 2018. On January 16, 2019, the federal government agency customer provided notification of final acceptance as of December 14, 2018. At December 31, 2018 , there was one financing contract that had not been novated to WGL Energy Systems for which draws totaling $ 15.5 million were reflected on the Washington Gas balance sheet as a short-term obligation to third-party lenders in "Notes payable and project financing". As of December 31, 2018 , Washington Gas recorded $ 85.3 million of contract assets in "Unbilled revenues", $ 15.5 million in a corresponding short-term obligation to third-party lenders in "Notes payable and project financing", and $69.7 million obligation to WGL Energy Systems in "Payables to associated companies" for energy management services projects that were not complete. As of September 30, 2018, Washington Gas recorded $ 77.0 million of contract assets in "Unbilled revenues", $ 68.5 million in "Notes payable and project financing", and $ 8.5 million in "Payables to associated companies" on the balance sheet. As of September 30, 2017, Washington Gas recorded $ 85.6 million of contract assets in " Unbilled revenue", $43.8 million in "Notes payable and project financing", and $ 41.8 million "Payables to associated companies" on the balance sheet. For projects where WGL Energy Systems is the primary contractor and where these projects are financed for government agencies that have minimal credit risk, and with which we have previous collection experience, Washington Gas did not record a corresponding reserve for bad debts related to these receivables at December 31, 2018 , September 30, 2018, or September 30, 2017.

Long-Term Debt

Long-Term Debt	3 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Long-Term Debt	LONG-TERM DEBT FIRST MORTGAGE BONDS The Mortgage of Washington Gas dated January 1, 1933 (Mortgage), as supplemented and amended, securing any First Mortgage Bonds (FMBs) it issues, constitutes a direct lien on substantially all property and franchises owned by Washington Gas, other than a small amount of property that is expressly excluded. At December 31, 2018 , September 30, 2018 and September 30, 2017 , Washington Gas had no debt outstanding under the Mortgage. Any FMBs that may be issued in the future will represent indebtedness of Washington Gas. SHELF REGISTRATION At December 31, 2018, Washington Gas had capacity under a shelf registration statement that was filed in May 2018 to issue up to $ 725.0 million of additional medium-term notes (MTN's). UNSECURED NOTES Washington Gas issues long-term debt in the form of MTNs, unsecured long-term notes and private placement notes with individual terms regarding interest rates, maturities and call or put options. These notes can have maturity dates of one or more years from the date of issuance. The following tables show the outstanding notes with maturities in calendar years as of December 31, 2018 , and maturities in fiscal years as of September 30, 2018 and September 30, 2017 . Long Term Debt Outstanding December 31, 2018 ($ In millions) Due calendar year 2019, 4.76% $ 50.0 Due calendar year 2023, 6.65% 20.0 Due calendar year 2025, 5.44% 40.5 Due calendar year 2026, 6.62% to 6.82% 53.0 Due calendar year 2027, 6.40% to 6.57% 72.0 Due calendar year 2028, 6.57% to 6.85% 52.0 Due calendar year 2030, 7.50% 8.5 Due calendar year 2036, 5.70% to 5.78% 50.0 Due calendar year 2040, 5.21% 75.0 Due calendar year 2043, 5.00% 75.0 Due calendar year 2044, 4.22% to 4.24% 150.0 Due calendar year 2046, 3.80% 450.0 Total Long-Term Debt (a) $ 1,096.0 Unamortized discount (2.9 ) Unamortized debt expense (8.1 ) Less—current maturities 50.0 Total Long-Term Debt $ 1,035.0 Weighted average interest rate (b) 4.77 % (a) Includes MTNs and private placement notes. The amount represents face value of long-term debt including current maturities. (b) Weighted average interest rate is for the long-term debt including current maturities . Long Term Debt Outstanding September 30, ($ In millions) 2018 2017 Due fiscal year 2019, 7.46% $ 50.0 50.0 Due fiscal year 2020, 4.76% 50.0 50.0 Due fiscal year 2023, 6.65% 20.0 20.0 Due fiscal year 2025, 5.44% 40.5 40.5 Due fiscal year 2027, 6.40% to 6.82% 125.0 125.0 Due fiscal year 2028, 6.57% to 6.85% 52.0 52.0 Due fiscal year 2030, 7.50% 8.5 8.5 Due fiscal year 2036, 5.70% to 5.78% 50.0 50.0 Due fiscal year 2041, 5.21% 75.0 75.0 Due fiscal year 2044, 4.22% to 5.00% 175.0 175.0 Due fiscal year 2045, 4.24% 50.0 50.0 Due fiscal year 2046, 3.80% 450.0 450.0 Total Long-Term Debt (a) $ 1,146.0 1,146.0 Unamortized discount (2.9 ) (3.0 ) Unamortized debt expense (8.1 ) (8.5 ) Less—current maturities 50.0 — Total Long-Term Debt $ 1,085.0 1,134.5 Weighted average interest rate (b) 4.89 % 4.89 % (a) Includes MTNs and private placement notes. The amount represents face value of long-term debt including current maturities. (b) Weighted average interest rate is for the long-term debt including current maturities. As of December 31, 2018 , the principal amounts of long-term debt due in each of the next five calendar years are $ 50 million , $ 20 million , and $ 1,026 million for 2019, 2023 and thereafter, respectively. The indenture for the unsecured MTNs and the note purchase agreement for the private placement notes provide that Washington Gas will not issue any FMBs under its Mortgage without securing all MTNs and the private placement notes with the Mortgage. Certain of Washington Gas’ outstanding MTNs and private placement notes have a make-whole call feature that pays the holder a premium based on a spread over the yield to maturity of a U.S. Treasury security having a comparable maturity if that particular note were to be called by Washington Gas before its stated maturity date. With the exception of this make-whole call feature, Washington Gas is not required to pay call premiums for calling debt prior to the stated maturity date. The following table shows long-term debt issuances and retirements for the three months ended December 31, 2018 , and fiscal year ended September 30, 2017. There were no issuances or retirements during the fiscal year ended September 30, 2018. Long-Term Debt Issuances and Retirements ($ In millions) Principal (a) Interest Rate (b) Effective Cost (b) Nominal Maturity Date Three Months Ended December 31, 2018 Retirements: 12/05/2018 $ 50.0 7.46 % 7.46 % 12/5/2018 Total $ 50.0 Year ended September 30, 2017 Issuances: 9/18/2017 $ 200.0 3.80 % 9/15/2046 Total $ 200.0 (a) Represents face amount of notes. (b) Represents the interest rate and effective cost at the trade date of the debt.

Preferred Stock

Preferred Stock	3 Months Ended
	Dec. 31, 2018
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock	PREFERRED STOCK Washington Gas has three series of cumulative preferred stock outstanding, and each series is subject to redemption by Washington Gas. All three series have a dividend preference that prohibits Washington Gas from declaring and paying dividends on shares of its common stock unless dividends on all outstanding shares of the preferred stock have been fully paid for all past quarterly dividend periods. In addition, all outstanding shares of preferred stock have a preference as to the amounts that would be distributed in the event of a liquidation or dissolution of Washington Gas. All three series of preferred stock are entitled to one vote per share. The following table presents this information, as well as call prices for each preferred stock series outstanding. Preferred Stock Preferred Liquidation Preference Series Shares Per Share Call Price Outstanding Outstanding Involuntary Voluntary Per Share $4.80 150,000 $100 $101 $101 $4.25 70,600 $100 $105 $105 $5.00 60,000 $100 $102 $102 On December 17, 2018, Washington Gas terminated the registration of its preferred stock with the SEC; however, the preferred stock remains outstanding.

Income Taxes

Income Taxes	3 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES Through July 6th and prior to the Merger with AltaGas, WGL and its wholly owned subsidiaries filed a consolidated federal income tax return and various state income tax returns where they had a business presence. We are no longer subject to income tax examinations by the Internal Revenue Service (IRS) for years ended September 30, 2013 and prior. Substantially all state income tax years in major jurisdictions are closed for years ended prior to September 30, 2015. Through July 6, 2018, WGL and each of its subsidiaries participated in a tax sharing agreement that establishes the method for allocating tax benefits from losses that are utilized on the consolidated income tax return. The consolidated tax is apportioned among the subsidiaries on the separate return method and losses are allocated to the subsidiaries that have taxable income pro-rata basis. Washington Gas paid $ 8.3 million to WGL's other subsidiaries for the three months ended December 31, 2018. For the fiscal year ended September 30, 2018, Washington Gas received $ 2.9 million from WGL's subsidiaries with taxable income for the utilization of Washington Gas' net operating loss pursuant to the tax sharing agreement. Effective with the Merger and beginning July 7, 2018, our tax year end changed to December 31 and Washington Gas will be included with AltaGas’ wholly owned US subsidiaries’ consolidated income tax return with AltaGas Services (U.S.), (ASUS) being the parent company of the consolidated group. Accordingly, Washington Gas will file a final return as part of the WGL 's consolidated income tax return for the short tax year from October 1, 2017 to July 6, 2018. WGL and its wholly owned subsidiaries will be included in the AltaGas' consolidated income tax returns beginning with the period from July 7, 2018 to December 31, 2018. We have established a new tax sharing policy with ASUS. The tax sharing policy provides allocation of consolidated tax liabilities and benefits based on amounts participants would incur as standalone corporations. Income taxes recorded for the period October 1, 2017 through July 6, 2018 are based on amounts we would incur as standalone corporations. State income tax returns are filed on a separate company basis in most states and on a unitary basis as required, where we or the consolidated ASUS group have operations and/or a requirement to file. In July 2018, we filed our tax return for the year ended September 30, 2017. US Federal Income Tax Reform On December 22, 2017, President Trump signed the Tax Cuts and Jobs Act (TCJA) (the Tax Act) into law. The Tax Act substantially reforms the Internal Revenue Code, including, but not limited to, (1) reducing the U.S. federal corporate tax rate from 35% to 21%; (2) creating a limitation on deductible interest expense equal to 30% of adjusted taxable income (not applicable to regulated utilities); (3) allowing 100% expensing for the cost of qualified property (generally not applicable to regulated utilities); (4) eliminating the domestic production activities deduction (not applicable to the consolidated tax group); (5) eliminating the corporate alternative minimum tax and changing how existing alternative minimum tax credits can be realized (not applicable to the consolidated tax group) in taxable years beginning after December 31, 2017; and (6) changing rules related to uses and limitations of net operating loss carry-forwards created in tax years beginning after December 31, 2017. ASC Topic 740 requires companies to recognize the impacts of a change in tax law or tax rates in the period of enactment. The most significant change that impacts the Registrants’ financial statements is the reduction of the corporate federal income tax rate from 35% to 21% beginning January 1, 2018. The Tax Act also made regulated public utilities ineligible for bonus depreciation. The IRS issued proposed transition rules for property acquired and placed into service after September 27, 2017. The TCJA repeals 50% bonus depreciation for all taxpayers and provides 100% expensing for assets for non-utility companies both acquired and placed-in-service after September 27, 2017. On August 8, 2018, the IRS issued proposed additional transition regulations allowing regulated utility companies to claim bonus depreciation for assets placed in service for the first year of implementation of The Act. For regulated utility companies, projects that were greater than 10% complete at September 27, 2017, are eligible for 50% bonus depreciation when placed into service. Assets less than 10% complete prior to September 27, 2017 and placed in service after September 27, 2017 are eligible for 100% bonus depreciation through the merger date of July 6, 2018. Projects that were greater than 10% complete at September 27, 2017 and placed in service after July 6, 2018 through December 31, 2018 are eligible for 40% bonus depreciation. We have recorded an amount consistent with our interpretation of the transition rule and the proposed depreciation regulation through December 31, 2018. Washington Gas has completed its assessment of the accounting for applicable effects of the Tax Act as allowed under SEC Staff Accounting Bulletin 118 (SAB 118), and has recorded applicable income tax amounts as of December 31, 2018. Items for which the accounting is complete by December 31, 2018, however may be subject to adjustment pursuant to Technical Corrections of The Act: Bonus depreciation: Under the Tax Act, regulated public utility property is ineligible for bonus depreciation and is depreciated under MACRS while non-utility property is eligible for 100% bonus depreciation. In accordance with the August 8, 2018 proposed depreciation regulations and the transitional rule above, an amount of $ 86.2 million of additional depreciation deduction for the short period ended July 6, 2018 has been recorded in fiscal year ended September 30, 2018. We have recognized an additional $ 17.4 million of bonus eligible assets for the three months ended December 31, 2018. Decrease in regulated revenues: In January 2018, Washington Gas filed applications for approval to reduce the distribution rates it charges customers in Maryland, Virginia and the District of Columbia to reflect the impact of the Tax Act. These applications proposed to reduce rates in these jurisdictions by a combined amount of $ 41.2 million annually, until base rates are reestablished in a general rate case. As described further below, the portion of this reduction in regulated revenues represented by the re-measurement of deferred tax assets and liabilities was recorded as a net regulatory liability under ASC 980, Regulated Operations. The net regulatory liability recorded is the amount we consider probable of regulatory treatment and will be refunded to customers in future periods. In addition, a portion of this reduction in regulated revenues relates to the federal tax expense at the new federal rate of 21% included in current base rates, effective January 1, 2018. Through the fiscal year ended September 30, 2018, revenues have been lowered by $ 27.5 million to reflect the regulatory impact of the Tax Act. For the three months ended December 31, 2018, the revenues have been lowered by an additional $ 13.7 million . Uncertain tax position: The re-measurement of Washington Gas’ uncertain tax position related to temporary difference associated with repairs expense was a decrease in the amount of $ 14.8 million . Generally, a reserve for uncertain tax benefits related to prior years would not be re-measured if the tax exposure related to prior years where the federal income tax rate was 35%. However, Washington Gas' reserve for uncertain tax benefits relates solely to repair deductions for which the tax consequence of any disallowed deductions related to these temporary differences is expected to be prospective only. For the three months ended December 31, 2018 there was no additional impact recognized associated with re-measurement. Re-measurement of deferred tax assets and liabilities: Under ASC 740, the tax rate used to measure deferred tax assets and liabilities are the tax rates expected to be in place when the liability is expected to be ultimately settled or the asset recovered. We re-measured deferred tax balances as of September 30, 2017. The re-measurement of our deferred tax assets and liabilities includes the impact on our cumulative prior year deferred tax asset net operating loss (DTA NOL), investment tax credit and related attributes and deferred taxes associated with our benefit plans. Through September 30, 2018, the effect of the re-measurement at a federal tax rate of 21% resulted in a net decrease in deferred tax liabilities in the amount of $ 421.7 million , including net tax gross-up, primarily related to the impact on plant-related deferred tax liabilities. The re-measurement of deferred tax assets not associated with rate-making are recorded as income tax expense of $ 7.0 million . Under ASC 980, we recorded a regulatory liability for excess deferred income taxes of $ 431.0 million including tax gross-up for the fiscal year ended September 30, 2018. Included in this amount. we recorded a decrease for flow-through depreciation related items and an increase for the re-measurement of non-plant excess deferred taxes (including the net operating loss carryforward deferred tax asset). These adjustments both included the appropriate tax gross-up. For the three months ended December 31, 2018, the final re-measurement implementation resulted in a net increase in deferred tax liabilities in the amount of $ 5.9 million , including net tax gross-up, and an increase to income tax expense of $ 1.2 million . For the three months ended December 31, 2018, under ASC 980, we reduced the net regulatory liability for excess deferred income taxes of $ 6.1 million including tax gross-up. For the twelve months ended September 30, 2018, the Company had cumulative taxable losses, and as a result, the Company has recorded its deferred tax liabilities at a federal rate of 21% because all amounts will reverse in future years when the rate is expected to be 21%. For the three months ended December 31, 2018, the re-measurement of all deferred tax assets and liabilities have been completed, including the re-measurement of the net operating loss. Accounting for the NOL DTA associated with the prior year return to provision true-up adjustments. Following the filing of our 2017 Federal income tax return, we recorded certain adjustments in the fourth quarter of 2018 to adjust our estimated taxes to the amounts included in the return. During the three months ended December 31, 2018, we have recorded the impacts of temporary differences on our deferred income tax balances resulting from these return to provision adjustments and have fully analyzed the impacts to the associated DTA - NOL and tax sharing. Components of Income Tax Expense or Benefit The following tables provide the components of income tax expenses for the three months ended December 31, 2018 and for fiscal years ended September 30, 2018, 2017 and 2016. Components of Income Tax Expense (Benefit) Three Months Ended December 31, Fiscal Years Ended September 30, (In thousands) 2018 2018 2017 2016 INCOME TAX EXPENSE Current: Federal $ — $ — $ 1,722 $ (48,064 ) State — 1,274 1,283 (2,957 ) Total current — 1,274 3,005 (51,021 ) Deferred: Federal Accelerated depreciation 6,494 (27,846 ) 83,009 93,385 Other 2,537 (8,485 ) (18,419 ) 13,826 State Accelerated depreciation 2,416 12,533 15,033 13,081 Other (3,435 ) (2,637 ) (2,037 ) 3,190 Total deferred (a) 8,012 (26,435 ) 77,586 123,482 Amortization of investment tax credits (165 ) (702 ) (751 ) (795 ) Total income tax expense (benefit) $ 7,847 $ (25,863 ) $ 79,840 $ 71,666 (a) Includes tax expense of $ 1.2 million and $ 7.0 million related to re-measurement of deferred income taxes for the three months ended December 31, 2018 and the fiscal year ended September 30, 2018, respectively. Rate Reconciliation The effective income tax rate from continuing operations varies from the U.S. Federal statutory rate principally due to the following: Reconciliation Between the Statutory Federal Income Tax Rate and Effective Tax Rate Three Months Ended December 31, Fiscal Years Ended September 30, ($ In thousands) 2018 2018 2017 2016 Income taxes at statutory federal income tax rate (a) $ 11,974 21.00 % $ (11,026 ) 21.00 % $ 74,071 35.00 % $ 64,673 35.00 % Increase (decrease) in income taxes resulting from: — Plant basis differences (4,261 ) (7.47 ) 1,079 (2.06 ) 2,213 1.05 2,445 1.32 Allowance for funds used during construction (520 ) (0.91 ) (70 ) 0.13 (291 ) (0.14 ) (509 ) (0.28 ) Amortization of investment tax credits (165 ) (0.29 ) (703 ) 1.34 (751 ) (0.35 ) (795 ) (0.43 ) Amortization of excess deferred taxes (2,431 ) (4.26 ) (9,798 ) 18.66 (196 ) (0.09 ) — — Cost of removal (28 ) (0.05 ) (1,561 ) 2.97 (2,944 ) (1.39 ) (3,722 ) (2.01 ) State income taxes-net of federal benefit 2,737 4.80 (2,659 ) 5.06 9,482 4.48 8,310 4.50 Consolidated tax sharing allocation — — — — — — 1,073 0.58 Re-measurement 1,243 2.18 7,031 (13.39 ) — — — — ASU 2016-09 adoption — — (3,223 ) 6.14 — — — — Return to provision adjustment — — (4,669 ) 8.89 (4,859 ) (2.30 ) (1,353 ) (0.73 ) Other items-net (702 ) (1.23 ) (264 ) 0.50 3,115 1.47 1,544 0.84 Total income tax expense (benefit) and effective tax rate $ 7,847 13.77 % $ (25,863 ) 49.24 % $ 79,840 37.73 % $ 71,666 38.79 % (a) As a result of the merger with AltaGas, Washington Gas is subject to two separate short periods and accompanying returns. The first period through July 6, 2018 is subjected to a higher, blended federal statutory rate. Due to the net operating loss for federal tax purposes through September 30, 2018, all the year activity is ultimately taxed at 21%. As such, for presentational purposes, we applied a 21% rate to the entire fiscal year 2018 activity. Components of accumulated deferred income tax assets and liabilities The following table provides the components of accumulated deferred income tax assets (liabilities) for Washington Gas at December 31, 2018, September 30, 2018 and September 30, 2017. Components of Accumulated Deferred Income Tax Assets (Liabilities) (In thousands) December 31, 2018 September 30, 2018 September 30, 2017 Deferred income tax assets: Pensions $ 25,629 $ 43,071 $ 41,907 Uncollectible accounts 1,680 1,131 7,815 Inventory overheads 4,088 4,090 6,617 Employee compensation and benefits 40,960 51,006 47,479 Derivatives 8,737 7,435 11,187 Income taxes recoverable through future rates 96,256 121,357 — Deferred gas costs — — 1,485 Net operating loss 84,674 90,943 — Total assets 262,024 319,033 116,490 Deferred income tax liabilities: Other post-retirement benefits 63,540 106,289 89,494 Accelerated depreciation and other plant related items 636,196 615,499 876,235 Losses/gains on reacquired debt 571 581 1,047 Income taxes recoverable through future rates — — 33,324 Deferred gas costs 14,928 3,041 — Other 1,037 3,430 4,775 Total liabilities 716,272 728,840 1,004,875 Net accumulated deferred income tax assets (liabilities) (454,248 ) $ (409,807 ) $ (888,385 ) The Company’s net operating losses generated through July 6, 2018 have expiration dates beginning in 2036. The Company’s investment tax credit carry forwards expire over various years beginning 2032. Tabular Reconciliation of Unrecognized Tax Benefits The following table summarizes the change in unrecognized tax benefits during the three months ended December 31, 2018, and the fiscal years of 2018, 2017, 2016, and our total unrecognized tax benefits at December 31, 2018 under the provisions of ASC Topic 740, Income Taxes: Unrecognized Tax Benefits For Fiscal Year Ended September 30, Three Months Ended December 31, Fiscal Year Ended September 30 (In thousands) 2018 2018 2017 2016 Total unrecognized tax benefits at beginning of the period $ 43,567 $ 48,009 $ 42,283 $ 38,627 Increases in tax positions relating to current period 2,574 10,947 10,766 10,645 Decreases in tax positions relating to prior periods (10,235 ) (15,389 ) (5,040 ) (6,989 ) Total unrecognized tax benefits at end of the period $ 35,906 $ 43,567 $ 48,009 $ 42,283 During the three months ended December 31, 2018 and the fiscal year ended September 30, 2018, the unrecognized tax benefits for Washington Gas decreased by approximately $ 7.7 million and $ 4.4 million , respectively, relating to uncertain tax positions, primarily due to the change in tax accounting for repairs and closed periods. If the amounts of unrecognized tax benefits are eventually realized, it would not materially impact the effective tax rate. It is reasonably possible that the amount of the unrecognized tax benefit with respect to some of Washington Gas’ uncertain tax positions will significantly increase or decrease in the next 12 months, if the IRS were to finalize and issue its proposed revenue procedure for gas distribution repair deductions. Amounts of Interest and Penalties Recognized Washington Gas recognizes any accrued interest associated with uncertain tax positions in interest expense and recognizes any accrued penalties associated with uncertain tax positions in other expenses in the statements of income. During the three months ended December 31, 2018 and the fiscal years ended September 30, 2018, 2017, and 2016, there was no accrued interest expense or penalties associated with uncertain tax positions.

Pension and Other Post-Retireme

Pension and Other Post-Retirement Benefit Plans	3 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Pension and Other Post-Retirement Benefit Plans	PENSION AND OTHER POST-RETIREMENT BENEFIT PLANS Washington Gas maintains a qualified, trusteed, non-contributory defined benefit pension plan (qualified pension plan) covering most active and vested former employees of Washington Gas and certain employees of WGL subsidiaries. The non-contributory defined benefit pension plan is closed to all employees hired on or after January 1, 2010 and instead employees are eligible to receive supplemental contributions to their defined-contribution savings plan. Several executive officers of Washington Gas also participate in a defined benefit supplemental executive retirement plan (DB SERP), a non-qualified pension plan. The DB SERP was closed to new entrants beginning January 1, 2010 and instead, executive officers are eligible to participate in a defined contribution SERP (DC SERP). In addition, effective January 1, 2010, Washington Gas established a non-funded defined benefit restoration plan (DB restoration) for the purpose of providing supplemental pension and pension-related benefits to a select group of management employees. There are rabbi trusts associated with the DB SERP and DB restoration plans that were funded pursuant to the Merger Agreement. The rabbi trusts can be used to make payments to the participants or the payments can be made from operating funds. At December 31, 2018 , the rabbi trust balance associated with these two plans was $60.8 million . $20.2 million was recorded in “Current Assets-Other” and $40.6 million was recorded in “Deferred Charges and Other Assets - Other”, along with other rabbi trust balances. Washington Gas accounts for the qualified pension plan, DB SERP and DB restoration plans under the provisions of ASC Topic 715, Compensation-Retirement Benefits. Washington Gas offers defined-contribution savings plans to all eligible employees. These plans allow participants to defer on a pre-tax or after-tax basis, a portion of their salaries for investment in various alternatives. We make matching contributions to the amounts contributed $ 1.1 million , $5.0 million , $4.6 million and $4.4 million during the three months ended December 31, 2018 and fiscal years ended September 30, 2018 , 2017 and 2016 , respectively. All employees not earning benefits in the qualified pension plan receive an employer provided supplemental contribution ranging from 4% to 6% depending on years of service. Total supplemental contributions to the plan were $ 0.7 million , $2.7 million , $2.2 million and $1.9 million during the three months ended December 31, 2018 and fiscal years ended September 30, 2018, 2017 and 2016 , respectively. Washington Gas provides certain healthcare and life insurance benefits for retired employees of Washington Gas and certain employees of WGL subsidiaries. Substantially all employees of Washington Gas may become eligible for such benefits if they attain retirement status while working for Washington Gas. For eligible retirees and dependents not yet receiving Medicare benefits, Washington Gas provides medical, prescription drug and dental benefits through Preferred Provider Organization (PPO) or Health Maintenance Organization (HMO) plans, through the Washington Gas Light Company Retiree Medical Plan (Retiree Medical Plan). For Medicare-eligible retirees age 65 and older , eligible retirees and dependents participate in a special tax-free HRA plan effective January 1, 2015. Participating retirees and dependents receive an annual subsidy to help purchase supplemental medical, prescription drug and dental coverage in the marketplace. As part of the new HRA plan, participants who enroll in a Medicare Part D prescription drug plan and meet the threshold for Medicare catastrophic prescription drug coverage will be eligible for an additional reimbursement of their out-of-pocket prescription drug costs in excess of the threshold. Washington Gas accounts for healthcare and life insurance benefits under the provisions of ASC Topic 715. On September 25, 2015, the Retiree Medical Plan was amended to limit the aggregate cost of applicable employer-sponsored coverage, thereby avoiding the 40% excise tax enacted by the Patient Protection and Affordable Care Act of 2010. The resolution, which was effective September 30, 2015 applies to plan years beginning on or after January 1, 2018, and includes a limit of $11,850 per participant, with a maximum limit of $30,950 for family coverage. This amendment resulted in a prior service credit of $26.1 million . Almost all costs associated with Washington Gas’ defined benefit post-retirement plans have historically been, and are expected to be, recovered through Washington Gas’ rates. Therefore, in accordance with ASC Topic 980 and ASC Topic 715, Washington Gas established a regulatory asset/liability for the substantial majority of the unrecognized costs/income associated with its defined benefit post-retirement plans. To the extent these amounts will not be recovered through Washington Gas’ rates, they are recorded directly to “Accumulated other comprehensive loss, net of taxes.” Obligations and Assets Washington Gas uses a measurement date of December 31, 2018 for its pension and retiree health care and life insurance benefits plans upon the changing of fiscal years. Previously, Washington Gas used a measurement date of September 30. The following table provides certain information about Washington Gas’ post-retirement benefits: Post-Retirement Benefits Pension Benefits (a) Health and Life Benefits Three Months Ended December 31, Fiscal Year Ended September 30, Three Months Ended December 31, Fiscal Year Ended September 30, (In millions) 2018 2018 2017 2018 2018 2017 Change in projected benefit obligation (b) Benefit obligation at beginning of period $ 989.8 $ 1,047.5 $ 1,069.3 $ 283.3 $ 309.0 $ 324.3 Service cost 3.0 14.9 16.5 1.3 5.3 5.8 Interest cost 10.6 39.6 38.4 3.0 11.7 11.7 Change in plan benefits 0.2 — — — — 1.1 Actuarial loss (gain) (17.3 ) (65.2 ) (28.2 ) (6.2 ) (28.7 ) (18.9 ) Retiree contributions and rebates — — — 0.9 1.9 1.8 Benefits paid (14.5 ) (47.0 ) (48.5 ) (4.4 ) (15.9 ) (16.8 ) Projected benefit obligation at end of period (b) $ 971.8 $ 989.8 $ 1,047.5 $ 277.9 $ 283.3 $ 309.0 Change in plan assets Fair value of plan assets at beginning of period $ 863.9 $ 872.5 $ 850.0 $ 569.3 $ 540.5 $ 505.0 Actual return on plan assets (42.3 ) 38.8 68.6 (32.0 ) 43.0 48.1 Company contributions 0.4 1.8 4.4 1.3 5.0 8.2 Retiree contributions and rebates — — — 0.9 1.9 1.8 Expenses (0.5 ) (2.2 ) (2.0 ) (6.3 ) (5.2 ) (5.8 ) Benefits paid (14.5 ) (47.0 ) (48.5 ) (4.4 ) (15.9 ) (16.8 ) Fair value of plan assets at end of period $ 807.0 $ 863.9 $ 872.5 $ 528.8 $ 569.3 $ 540.5 Funded status at end of period $ (164.8 ) $ (125.9 ) $ (175.0 ) $ 250.9 $ 286.0 $ 231.5 Allocation to affiliates $ (1.6 ) $ (1.3 ) $ (1.7 ) $ 1.4 $ 1.7 $ 1.2 Adjusted funded status at end of period (163.2 ) (124.6 ) (173.3 ) 249.5 284.3 230.3 Total amounts recognized on balance sheet Non-current asset $ — $ — $ — $ 249.5 $ 284.3 $ 230.3 Current liability (20.2 ) (20.2 ) (6.5 ) — — — Non-current liability (143.0 ) (104.4 ) (166.8 ) — — — Total recognized $ (163.2 ) $ (124.6 ) $ (173.3 ) $ 249.5 $ 284.3 $ 230.3 (a) The DB SERP and DB Restoration, included in pension benefits in the table above, does not include the amounts funded in rabbi trust. (b) For the Health and Life Benefits, the change in projected benefit obligation represents the accumulated benefit obligation. The following table provides the projected benefit obligation (PBO) and accumulated benefit obligation (ABO) for the qualified pension plan, DB SERP and DB Restoration at December 31, 2018 , September 30, 2018 and September 30, 2017 . Projected and accumulated benefit obligation Qualified Pension Plan DB SERP DB Restoration December 31, September 30, December 31, September 30, December 31, September 30, (In millions) 2018 2018 2017 2018 2018 2017 2018 2018 2017 Projected benefit obligation $ 906.2 $ 923.6 $ 983.1 $ 61.5 $ 62.2 $ 60.2 $ 4.1 $ 4.0 $ 4.2 Accumulated benefit obligation $ 847.1 $ 859.1 $ 905.8 $ 59.8 $ 60.7 $ 57.5 $ 3.2 $ 3.0 $ 3.0 Amounts Recognized in Regulatory Assets/Liabilities and Accumulated Other Comprehensive Income The following table provides amounts recorded to regulatory assets, regulatory liabilities and accumulated other comprehensive loss/(income) at December 31, 2018 , September 30, 2018 and September 30, 2017 : Unrecognized Costs/Income Recorded on the Balance Sheet Pension Benefits Health and Life Benefits December 31, September 30, December 31, September 30, (In millions) 2018 2018 2017 2018 2018 2017 Actuarial net loss (gain) $ 96.1 $ 61.0 $ 136.1 $ (26.0 ) $ (64.5 ) $ (21.8 ) Prior service cost (credit) 1.0 0.9 1.2 (102.8 ) (107.2 ) (124.9 ) Total (a) $ 97.1 $ 61.9 $ 137.3 $ (128.8 ) $ (171.7 ) $ (146.7 ) Regulatory asset (liability) (b) $ 80.8 $ 47.9 $ 118.8 $ (121.1 ) $ (159.4 ) $ (136.4 ) Pre-tax accumulated other comprehensive loss (income) (c) 15.9 13.7 17.7 (6.9 ) (11.2 ) (9.5 ) Total $ 96.7 $ 61.6 $ 136.5 $ (128.0 ) $ (170.6 ) $ (145.9 ) (a) Pension benefits include amounts allocated to affiliates of $ 0.4 million , $ 0.3 million and $ 0.8 million at December 31, 2018, September 30, 2018 and 2017, respectively; Health and Life Benefits includes amounts allocated to affiliates of $ 0.8 million , $ 1.1 million , and $ 0.8 million at December 31, 2018, September 30, 2018 and 2017, respectively. (b) The regulatory liability recorded on our balance sheet at September 30, 2018 and September 30, 2017 is net of a deferred income tax benefit of $ 0.2 million and $2.2 million , respectively. There is no deferred income tax benefit at December 31, 2018. (c) The total amount of accumulated other comprehensive loss recorded on our balance sheets at December 31, 2018 , September 30, 2018 and September 30, 2017 is net of an income tax benefit of $ 2.4 million , $0.7 million and $3.6 million , respectively. The following table provides amounts that are included in regulatory assets/liabilities and accumulated other comprehensive loss associated with our unrecognized pension and other post-retirement benefit costs that were recognized as components of net periodic benefit cost before allocations to affiliates and capital during the three months ending December 31, 2018 and the fiscal year ended September 30, 2018 . Amounts Recognized During the Three Months Ended December 31, 2018 Regulatory assets/liabilities Accumulated other (In millions) Pension Health and Pension Health and Actuarial net loss $ 1.0 $ — $ 0.4 $ — Prior service cost (credit) 0.1 (4.1 ) — (0.3 ) Total $ 1.1 $ (4.1 ) $ 0.4 $ (0.3 ) The following table provides amounts that are included in regulatory assets/liabilities and accumulated other comprehensive loss associated with our unrecognized pension and other post-retirement benefit costs that are expected to be recognized as components of net periodic benefit cost before allocations to affiliates and capital during 2019 . Amounts to be Recognized During Calendar Year 2019 Regulatory assets/liabilities Accumulated other comprehensive loss (In millions) Pension Benefits Health and Life Benefits Pension Benefits Health and Life Benefits Actuarial net loss $ 3.4 $ — $ 1.7 $ — Prior service cost (credit) 0.1 (15.0 ) 0.2 (0.8 ) Total $ 3.5 $ (15.0 ) $ 1.9 $ (0.8 ) Washington Gas also expects a partial settlement of the DB SERP to occur in first quarter of 2019, which will result in an estimated $ 4.1 million loss. Realized and unrealized gains and losses for assets under Washington Gas’ post-retirement benefit plans are spread over a period of five years. Each year, 20% of the prior five years’ asset gains and losses are recognized. The market-related value of assets is equal to the market value of assets less the following percentages of prior years’ realized and unrealized gains and losses on equities: 80% of the prior year, 60% of the second prior year, 40% of the third prior year and 20% of the fourth prior year. Net Periodic Benefit Cost The components of the net periodic benefit costs (income) for three months ended December 31, 2018 , and the years ended September 30, 2018, 2017 and 2016 related to pension and other post-retirement benefits were as follows: Components of Net Periodic Benefit Costs (Income) Pension Benefits Health and Life Benefits Three months ended December 31, Year Ended September 30, Three months ended December 31, Year Ended September 30, (In millions) 2018 2018 2017 2016 2018 2018 2017 2016 Service cost $ 3.0 $ 14.9 $ 16.5 $ 14.2 $ 1.3 $ 5.3 $ 5.8 $ 4.6 Interest cost 10.6 39.6 38.4 41.3 3.0 11.7 11.7 13.1 Expected return on plan assets (10.9 ) (42.3 ) (41.0 ) (40.9 ) (6.1 ) (23.7 ) (22.1 ) (20.4 ) Recognized prior service cost (credit) 0.1 0.3 0.3 0.3 (4.4 ) (17.6 ) (17.7 ) (17.7 ) Recognized actuarial loss 1.4 15.6 22.0 16.9 — — 1.9 1.2 Net periodic benefit cost (income) 4.2 28.1 36.2 31.8 (6.2 ) (24.3 ) (20.4 ) (19.2 ) Allocation to affiliates (0.4 ) (4.2 ) (2.9 ) (1.9 ) 0.8 3.1 1.4 1.1 Adjusted net periodic benefit cost (income) 3.8 23.9 33.3 29.9 (5.4 ) (21.2 ) (19.0 ) (18.1 ) Amount allocated to construction projects (a) (0.6 ) (4.7 ) (6.4 ) (5.6 ) (0.2 ) 4.0 4.6 4.1 Amount deferred as regulatory asset (liability)-net allocations 1.5 5.9 6.9 7.1 — — — (0.2 ) Amount charged (credited) to expense $ 4.7 $ 25.1 $ 33.8 $ 31.4 $ (5.6 ) $ (17.2 ) $ (14.4 ) $ (14.2 ) (a) On October 1, 2018, Washington Gas prospectively adopted ASU 2017-07. As a result, only the service cost component of net periodic benefit costs (income) is eligible for capitalization. Amounts included in the line item “Amount deferred as regulatory asset/liability-net,” as shown in the table above, represent the amortization of previously unrecovered costs of the applicable pension benefits or the health and life benefits as approved in the District of Columbia through 2019. On October 1, 2018, Washington Gas adopted ASU 2017-07. This standard requires entities to report the service cost component in the same financial statement line item as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are to be presented separately from service cost and outside of operating income. Washington Gas includes the other components in "Other Income (expense)-net" on the three months ended December 31, 2018 Statement of Income. In addition, only the service cost component of net benefit cost is eligible for capitalization. Changes to the presentation of service costs and other components of net benefit cost were applied retrospectively. As a result of the retrospective adoption, we reclassified $ 11.3 million , $ 3.9 million and $ 3.6 million , respectively, of net periodic benefit income from "Operation and maintenance" expense to "Other income (expense)-net" on the September 30, 2018, 2017 and 2016 Statement of Income. Changes in capitalization practices were implemented prospectively. Assumptions The weighted average assumptions used to determine net periodic benefit obligations and net periodic benefit costs were as follows: Benefit Obligations Assumptions Pension Benefits Health and Life Benefits Three months ended December 31, Fiscal Year ended September 30, Three months ended December 31, Fiscal Year ended September 30, 2018 2018 2017 2016 2018 2018 2017 2016 Discount rate (a) 4.30%-4.40% 4.30%-4.40% 3.60%-3.90% 3.40%-3.70% 4.40 % 4.40 % 3.90 % 3.70 % Rate of compensation increase 3.50%-4.10% 3.50%-4.10% 3.50%-4.10% 3.50%-4.10% 4.10 % 4.10 % 4.10 % 4.10 % (a) The increase in the discount rate in the three months ended December 31, 2018 and fiscal year 2018 compared to prior years primarily reflects the increase in long-term interest rates. Net Periodic Benefit Cost Assumptions Pension Benefits Health and Life Benefits Three months ended December 31, Year ended September 30, Three months ended December 31, Year ended September 30, 2018 2018 2017 2016 2018 2018 2017 2016 Discount rate (a) 4.30%-4.40% 3.60%-3.90% 3.40%-3.70% 4.10%-4.50% 4.40 % 3.90 % 3.70 % 4.50 % Expected long-term return on plan assets (b) 5.75 % 5.75 % 5.75 % 6.00 % 5.25 % 5.50 % 5.50 % 5.75 % Rate of compensation increase (c) 3.50%-4.10% 3.50%-4.10% 3.50%-4.10% 3.50%-4.10% 4.10 % 4.10 % 4.10 % 4.10 % (a) The changes in the discount rates over the last three fiscal years primarily reflect the changes in long-term interest rates. (b) For health and life benefits, the expected returns for certain funds may be lower due to certain portions of income that are subject to an assumed income tax rate of 42.2% . (c) The changes in the rate of compensation reflects the best estimates of actual future compensation levels including consideration of general price levels, productivity, seniority, promotion, and other factors such as inflation rates. Discount Rate Washington Gas determines the discount rate based on a portfolio of high quality fixed-income investments (AA- as assigned by Standard & Poor’s or Aa3 as assigned by Moody’s or better) whose cash flows would cover our expected benefit payments. Expected long-term return on plan assets Washington Gas determines the expected long-term rate of return on plan assets by averaging the expected earnings for the target asset portfolio. In developing the expected rate of return assumption, Washington Gas evaluates an analysis of historical actual performance and long-term return projections, which gives consideration to our asset mix and anticipated length of obligation of our plan. Mortality Assumptions On October 27, 2014, the SOA published updated mortality tables for U.S. plans (RP-2014) and an updated improvement scale (MP-2014), which both reflect improved longevity. The SOA also issued updated improvement scales each year thereafter, of which the latest is MP-2018. The RP-2014 mortality table and MP-2018 improvement scale were used to determine the benefit obligation as of December 31, 2018. The benefit obligations as of September 30, 2018 and 2017 were determined using the RP-2014 mortality tables and a modified improvement scale. We modified the MP-2014 improvement scale to (a) adjust the ultimate long-term rate of mortality improvement from 1.00% to 0.75% per annum up to age 85 trending down to 0% between age 85 and age 115; and (b) shorten the convergence period from short term to ultimate rates of improvement from the 20-year period to a 15-year period. Healthcare cost trend Washington Gas assumed the healthcare cost trend rates related to the accumulated post-retirement benefit obligation as of December 31, 2018 , for non-Medicare eligible retirees, to be 6.5% for calendar year 2019 . Washington Gas expects the trend rate to decrease to 2.1% in calendar year 2020 and remain at that level thereafter. Healthcare Trend (In millions) One Percentage-Point Increase One Percentage-Point Decrease Increase (decrease) total service and interest cost components $ 0.2 $ (0.1 ) Increase (decrease) post-retirement benefit obligation $ 5.2 $ (4.6 ) For Medicare eligible retirees age 65 and older that will receive a subsidy each year as a benefit from the HRA plan, Washington Gas assumed no increase to the annual subsidy in calendar years 2018 and 2019 and a 3.0% increase thereafter in order to approximate possible future increases to the stipend. While the plan terms do not guarantee increases to the stipend, Washington Gas intends to review the stipend annually. Investment Policies and Strategies The investment objective of the qualified pension, healthcare, and life insurance benefit plans (“Plan” or “Plans”) is to allocate each Plan’s assets to appropriate investment asset classes (asset categories) so that the benefit obligations of each Plan are adequately funded, consistent with appropriate risk tolerance guidelines for the Plans’ and Washington Gas’ tolerance for risk. Washington Gas' portion of retired employee healthcare and life insurance benefits obligation is funded through two trusts: (i) the Washington Gas Light Company Post Retirement Benefit Master Trust for Retired Previously Union-Eligible Employees ("union-eligible trust") and (ii) the Washington Gas Light Company Post Retirement Benefit Master Trust for Retired Management Employees ("management trust"). In order to best achieve the investment objectives for each Plan, strategic allocation targets and ranges are established that control exposure to selected investment asset classes. Target qualified pension plan trust asset allocations are 32% U.S. Equities, 8% International Equities, 5% Real Estate and 55% Fixed Income. Target asset class allocations for the union-eligible and management trusts were modified during August 2018. At December 31, 2018 , target union-eligible trust asset class allocations are 40% U.S. Large-Cap Equities and 60% Fixed Income and target management trust asset class allocations are 50% U.S. Large-Cap Equities and 50% Fixed Income. Actual asset balances are reviewed monthly and allowed to range within plus or minus 5% or less of the target allocations. Assets are generally rebalanced to target allocations before actual amounts fall below or rise above the allowable ranges. Asset/liability modeling (ALM) is used to test the benefits and risks of several potential strategic asset allocation mixes. Simulated investment performance results based on assumptions about expected return, volatility, and correlation characteristics of the selected asset classes are tested for their effects on contributions, pension expense, PBO funded status, and downside Value at Risk metrics over a ten-year planning time horizon. Important outcomes from past ALM studies include decisions to increase fixed income exposure, lengthen the duration of those fixed income assets and implement a dynamic asset allocation strategy that allows for the de-risking of the qualified pension plan portfolio over time. The dynamic asset allocation strategy resulted in a qualified pension plan portfolio de-risking during May 2017 when Fixed Income and U.S. Equities exposures were increased and reduced, respectively. The most recent qualified pension plan ALM study was completed during February 2018. An outcome of the 2018 ALM study was that the dynamic asset allocation strategy was adjusted so that the target fixed income allocation percentage will be increased by 10% (versus a 5% increase previously) for each 5% improvement in the qualified pension plan’s funded ratio, as measured by an investment consultant. The 2018 ALM study did not result in any other significant changes to investment strategy. Significant amounts of each various Plan's assets are managed by the same financial institution. Each Plan has a high exposure to U.S. based investments. There are no other significant risk concentrations related to investments in any entity, industry, country, commodity, or investment fund. Commingled funds are employed in the management of qualified pension plan, management trust, and union-eligible trust assets. In addition, a publicly offerable mutual fund and separately managed portfolios are employed in the management of a qualified pension plan trust. The management trust also utilizes a separately managed portfolio. U.S. and international equity assets are diversified across sectors, industries, and investment styles. Fixed income assets are primarily diversified across U.S. government and investment grade corporate debt instruments, with some exposure to foreign sovereign debt and minor exposure to non-investment-grade securities. Real estate is diversified geographically across the U.S. by property type. The qualified pension plan’s investment policy allows the use of futures, options, and other derivatives for purposes of reducing portfolio risk and as a low-cost option for gaining market exposure, but derivatives may not be used for leverage. The qualified pension plan’s investment policy prohibits investments in Washington Gas securities. The prohibition applies to separately managed portfolios but does not apply to any commingled fund investments. The following tables present the fair value of the pension plan assets and health and life insurance plan assets by asset category as of December 31, 2018 , September 30, 2018 and September 30, 2017 . Pension Plan Assets % of ($ In millions) Level 1 Level 2 Level 3 Total Total At December 31, 2018 Cash and cash equivalents $ 0.7 $ — $ — $ 0.7 0.1 % Equity securities Preferred Securities — 1.9 — 1.9 0.2 Fixed income securities U.S. Treasuries — 133.2 — 133.2 16.5 U.S. Corporate Debt — 216.4 — 216.4 26.8 U.S. Agency Obligations and Government Sponsored Entities — 27.5 — 27.5 3.4 Asset-Backed Securities — 0.5 — 0.5 0.1 Municipalities — 8.3 — 8.3 1.0 Non-U.S. Corporate Debt — 46.7 — 46.7 5.8 Other (a) — 4.9 — 4.9 0.6 Mutual Funds (b) 36.4 — — 36.4 4.5 Derivatives (c) — 6.8 — 6.8 0.8 Total investments in the fair value hierarchy $ 37.1 $ 446.2 $ — $ 483.3 59.8 % Investments measured at net asset value using the NAV practical expedient (d) Commingled Funds and Pooled Separate Accounts (e) 289.6 35.9 % Private Equity/Limited Partnership (f) 35.3 4.4 % Total fair value of plan investments 808.2 100.1 % Net receivable (payable) (g) (1.2 ) (0.1 ) Total plan assets at fair value (h) $ 807.0 100.0 % Pension Plan Assets % of ($ In millions) Level 1 Level 2 Level 3 Total Total At September 30, 2018 Cash and cash equivalents $ 2.2 $ — $ — $ 2.2 0.3 % Equity securities Preferred Securities — 2.1 — 2.1 0.2 Fixed income securities U.S. Treasuries — 127.6 — 127.6 14.8 U.S. Corporate Debt — 227.8 — 227.8 26.4 U.S. Agency Obligations and Government Sponsored Entities — 28.3 — 28.3 3.3 Asset-Backed Securities — 0.5 — 0.5 0.1 Municipalities — 8.3 — 8.3 1.0 Non-U.S. Corporate Debt — 47.1 — 47.1 5.5 Other (a) — 5.2 — 5.2 0.6 Mutual Funds (b) 42.4 — — 42.4 4.9 Derivatives (c) — 1.1 — 1.1 0.1 Total investments in the fair value hierarchy $ 44.6 $ 448.0 $ — $ 492.6 57.2 % Investments measured at net asset value using the NAV practical expedient (d) Commingled Funds and Pooled Separate Accounts (e) 329.3 38.0 % Private Equity/Limited Partnership (f) 39.1 4.5 % Total fair value of plan investments 861.0 99.7 % Net receivable (g) 2.9 0.3 Total plan assets at fair value (i) $ 863.9 100.0 % Pension Plan Assets % of ($ In millions) Level 1 Level 2 Level 3 Total Total At September 30, 2017 Cash and cash equivalents $ 0.7 $ — $ — $ 0.7 0.1 % Equity securities Preferred Securities — 0.6 — 0.6 0.1 Fixed income securities U.S. Treasuries — 140.9 — 140.9 16.2 U.S. Corporate Debt — 232.3 — 232.3 26.6 U.S. Agency Obligations and Government Sponsored Entities — 20.0 — 20.0 2.3 Asset-Backed Securities — 2.0 — 2.0 0.2 Municipalities — 14.9 — 14.9 1.7 Non-U.S. Corporate Debt — 48.1 — 48.1 5.5 Repurchase Agreement (i) 3.7 3.7 0.4 Other (a) — 6.7 — 6.7 0.8 Mutual Funds (b) 41.4 — — 41.4 4.7 Derivatives (c) — 1.9 — 1.9 0.2 Total investments in the fair value hierarchy $ 42.1 $ 471.1 $ — $ 513.2 58.8 % Investments measured at net asset value using the NAV practical expedient (d) Commingled Funds and Pooled Separate Accounts (e) $ 324.4 37.2 % Private Equity/Limited Partnership (f) $ 37.6 4.3 % Total fair value of plan investments 875.2 100.3 % Net payable (g) (2.7 ) (0.3 ) Total plan assets at fair value $ 872.5 100.0 % (a) This category primarily includes non-U.S. government bonds as of December 31, 2018 and September 30, 2018 and 2017 . (b) At December 31, 2018 and September 30, 2018 and 2017 , the investment in a mutual fund consisted primarily of common stock of non-U.S. based companies. (c) At December 31, 2018 and September 30, 2018 and 2017 , this category included a combination of long-term U.S. Treasury interest rate future contracts, currency forwards, currency option interest rate swaps, and put and call options on both interest rate swaps and credit default swap index products. (d) In accordance with ASC Topic 820, these investments are measured at fair value using NAV per share as a practical expedient and, therefore, have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliations of the fair value hierarchy to the statements of net assets available for plan benefits. (e) As of December 31, 2018 investments in commingled funds and a pooled separate account consisted of approximately 89% common stock U.S companies; 9% income producing properties located in the United States; and 1% short-term money market investments. As of September 30, 2018 and 2017 , investments in commingled funds and a pooled separate account consisted of approximately 90% common stock U.S companies; 8% income producing properties located in the United States; and 2% short-term money market investments. (f) At December 31, 2018 and September 30, 2018 and 2017 , investments in a private equity/limited partnership consisted of common stock of international companies. (g) At December 31, 2018 and September 30, 2018 and 2017 , this net payable primarily represents pending trades for investments purchased net of pending trades for investments sold and interest receivable. (h) This table does not include rabbi trust investments located in "Current Assets-Other" and "Deferred Charges and Other Assets-Other" on our balance sheets. Refer to Note 14— Fair Value Measurements for fair value of rabbi trust investments. (i) This category includes Treasury Bills with a pre-commitment from the counterparty to repurchase the same securities on the next business day at an agreed-upon price. Healthcare and Life Insurance Plan Assets % of ($ In millions) Level 1 Level 2 Level 3 Total Total At December 31, 2018 Cash and Cash Equivalents $ 3.2 $ — $ — $ 3.2 0.6 % Fixed Income Securities U.S Agency Obligations — 1.9 — 1.9 0.4 U.S. Treasuries — 51.2 — 51.2 9.7 U.S. Corporate Debt — 51.6 — 51.6 9.8 Municipalities — 4.5 — 4.5 0.8 Non-U.S. Corporate Debt — 8.5 — 8.5 1.6 Other (a) — 3.3 — 3.3 0.6 Total investments in the fair value hierarchy $ 3.2 $ 121.0 $ — $ 124.2 23.5 % Investments measured at net asset value using the NAV practical expedient (b) Commingled Funds (c) 403.3 76.3 % Total fair value of plan investments 527.5 99.8 % Net receivable (d) 1.3 0.2 Total plan assets at fair value $ 528.8 100.0 % Healthcare and Life Insurance Plan Assets % of ($ In millions) Level 1 Level 2 Level 3 Total Total At September 30, 2018 Cash and Cash Equivalents $ 2.9 $ — $ — $ 2.9 0.5 % Fixed Income Securities U.S Agency Obligations — 1.9 — 1.9 0.3 U.S. Treasuries — 50.1 — 50.1 8.8 U.S. Corporate Debt — 55.0 — 55.0 9.7 Municipalities — 4.7 — 4.7 0.8 Non-U.S. Corporate Debt — 9.1 — 9.1 1.6 Other (a) — 3.4 — 3.4 0.6 Total investments in the fair value hierarchy $ 2.9 $ 124.2 $ — $ 127.1 22.3 % Investments measured at net asset value using the NAV practical expedient (b) Commingled Funds (c) 441.6 77.6 % Total fair value of plan investments 568.7 99.9 % Net receivable (d) 0.6 0.1 Total plan assets at fair value $ 569.3 100.0 % At September 30, 2017 Cash and Cash Equivalents $ 2.6 $ — $ — $ 2.6 0.5 % Fixed Income Securities U.S Agency Obligations — 1.7 — 1.7 0.3 U.S. Treasuries — 36.0 — 36.0 6.7 U.S. Corporate Debt — 41.9 — 41.9 7.8 Municipalities — 3.6 — 3.6 0.7 Non-U.S. Corporate Debt — 7.2 — 7.2 1.3 Other (a) — 2.8 — 2.8 0.5 Total investments in the fair value hierarchy $ 2.6 $ 93.2 $ — $ 95.8 17.8 % Investments measured at net asset value using the NAV practical expedient (b) Commingled Funds (c) 444.0 82.1 % Total fair value of plan investments 539.8 99.9 % Net receivable (d) 0.7 0.1 Total plan assets at fair value $ 540.5 100.0 % (a) At December 31, 2018 and September 30, 2018 and 2017 , this category consisted primarily of non-U.S. government bonds. (b) In accordance with ASC Topic 820, these investments are measured at fair value using Net Asset Value (NAV) per share as a practical expedient and, therefore, have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliations of the fair value hierarchy to the statements of net assets available for plan benefits. (c) At December 31, 2018, investments held by commingled funds in which the plan invests consisted of 54% of common stock of large-cap U.S. companies, 20% of US Govt fixed income securities and 26% corporate bonds. At September 30, 2018, investments held by commingled funds in which the plan invests consisted primarily of 58% of common stock of large-cap U.S. companies, 17% of U.S. Government fixed income securities and 25% of corporate bonds. At September 30, 2017 , investments held by commingled funds in which the plan invests consisted primarily of 67% of common stock

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	STOCK-BASED COMPENSATION Stock-Based Compensation for Key Employees We have stock-based awards outstanding in the form of performance units and restricted units. In March 2016, WGL adopted a shareholder-approved Omnibus Plan (2016 Plan) to replace, on a prospective basis, the Omnibus Incentive Plan (2007 Plan). Stock options, stock appreciation rights, restricted stock, deferred stock as a bonus or awards in lieu of obligations, dividend equivalents, other stock-based awards and cash awards may be granted under the 2016 Plan. Effective upon the Merger with AltaGas, WGL no longer has common stock outstanding and no new awards will be issued in WGL stock. Description of Current Awards Washington Gas has stock-based awards outstanding in the form of performance units and restricted units. Performance units have a three-year vesting period, are settled in cash and are accounted for as liability awards. Restricted units have annual vesting over the three-year period, are settled in cash and are accounted for as deferred compensation under ASC 710. Performance Units Performance units earned pursuant to terms of the grant are paid in cash and are valued at $1.00 per performance unit. A portion of the performance units vest from zero to 200 percent of the target award based on our return on equity ratio achieved during the performance period, which is a performance condition under ASC Topic 718 (ROE Award). The resulting payout is also adjusted from 80 to 120 percent by a modifier based on AltaGas' total shareholder return relative to a selected peer group of companies (TSR Modifier), which is a market condition under ASC Topic 718. A portion of the performance units vest from zero to 200 percent of the target award based on our three-year adjusted funds from operation compounded growth during the performance period, which is a performance condition under ASC Topic 718 (AFFO Award). The resulting payout if also adjusted by a TSR Modifier. Our performance units are accounted for as liability awards under ASC 718 as they only settle in cash; therefore, we measure and record compensation expense for these awards based on their fair value at the end of each period until their vesting date. The percentage of the fair value that is accrued as compensation expense at the end of each period equals the percentage of the requisite service that has been rendered at that date. Consequently, fluctuations in earnings may result. Restricted Units Restricted units earned pursuant to terms of the grant are paid in cash at the end of each year and are valued at $ 1.00 per restricted unit. One third of the restricted units vest at the end of each year in the three-year period if AltaGas pays a dividend during that period. Our restricted units are accounted for under ASC 710 as they only settle in cash and do not have a market condition; therefore, we measure and record compensation expense for these awards based on the probable payment at the end of each period. The percentage of the probable payment that is accrued as compensation expense at the end of each period equals the percentage of the requisite service that has been rendered at that date. The following tables summarize information regarding performance unit and restricted unit activity during the three months ended December 31, 2018 . Performance Unit Activity Three Months Ended December 31, 2018 Number of Units Non-vested and outstanding, beginning of the quarter — Granted 5,934,828 Settled — Canceled/forfeited — Non-vested and outstanding, end of year 5,934,828 Restricted Unit Activity Three Months Ended December 31, 2018 Number of Units Non-vested and outstanding, beginning of the quarter — Granted 2,253,585 Settled — Canceled/forfeited — Non-vested and outstanding, end of year 2,253,585 For the three months ended December 31, 2018, we recognized $0.3 million compensation expense related to the performance units and restricted units. As of December 31, 2018, total unrecognized compensation expense related to the current stock-based awards is $6.5 million , which will be recognized over a period of 2.75 years. As of December 31, 2018, we recorded a deferred liability of $0.7 million related to the grant in “Deferred Credits-other”. Description of Prior Awards Prior to the Merger with AltaGas, Washington Gas had stock-based awards outstanding in the form of performance shares and performance units. All stock-based awards outstanding had a three -year vesting period. Performance shares were accounted for as equity awards, and performance units were accounted for as liability awards as they were settled in cash. Both awards were subject to certain market or performance conditions and provided for accelerated vesting upon a change in control of WGL under certain circumstances. Upon the Merger with AltaGas, the awards granted in fiscal years 2017 and 2016 were accelerated and became fully vested. The awards granted in fiscal year 2018 were converted to a fixed cash amount and still require vesting over the three-year period. See the Modification section below for a more detailed discussion of the impact. For the fiscal year ended September 30, 2018, we recognized $15.8 million compensation expense, of which $7.7 million related to the modification event described below. A $4.9 million income tax benefit was related to the compensation expense. For the fiscal years ended September 30, 2017 and 2016, we recognized stock-based compensation expense of $12.2 million and $10.1 million , respectively, and related income tax benefits of $6.1 million and $4.5 million , respectively. Performance Shares For performance shares granted in fiscal years 2017 and 2016, half of the performance shares vested from zero to 200 percent of the target award based on WGL's total shareholder return relative to a selected peer group of companies, which is a market condition under ASC Topic 718 (TSR Award). The remaining half of the performance shares granted in fiscal years 2017 and 2016 vested if our non-GAAP operating earnings per share on a diluted basis exceed dividends paid per share of common stock during the performance period, which is a performance condition under ASC Topic 718 (Dividend Coverage Award). For performance shares granted in fiscal year 2018, half of the performance shares were ROE Awards. The remaining half of the performance shares granted in fiscal year 2018 were Dividend Coverage Awards. We recognized compensation expense related to performance shares over the three -year requisite service period. Compensation expense for performance shares that vest based on the satisfaction of a performance condition was recognized for awards that ultimately vest and was adjusted to the actual outcome of the performance condition. Compensation expense for performance shares that vest based on the satisfaction of a market condition was recognized at the grant date fair value if the requisite service is rendered, but is not adjusted to reflect the ultimate achievement of the market condition. The fair value of each performance share that vests based on the satisfaction of a market condition was estimated using a Monte Carlo simulation model at the grant date. The total intrinsic value of performance shares vested during the year ended September 30, 2018 and 2017 was $16.7 million and $9.9 million , respectively. Performance Units Performance units earned pursuant to terms of the grant were paid in cash and valued at $ 1.00 per performance unit. For performance units granted in fiscal years 2017 and 2016, half of the performance units were TSR Awards and half were ROE Awards. All the performance units granted in fiscal year 2018 were ROE Awards. Our performance units were liability awards as they only settled in cash; therefore, we measured and recorded compensation expense for these awards based on their fair value at the end of each period until their vesting date. The percentage of the fair value that was accrued as compensation expense at the end of each period equaled the percentage of the requisite service that had been rendered at that date. Consequently, fluctuations in earnings could result, that did not occur under the accounting requirements for our performance shares. The fair value of each performance unit that vests based on the satisfaction of a market condition was estimated using a Monte Carlo simulation model. The fair value of each performance unit that vests based on the satisfaction of a performance condition was $1.00 . The amount of total compensation cost to be recognized for these performance units was a function of this fair value and the number of awards vested as a result of the performance condition being met and the requisite service provided. As of September 30, 2017, we recorded a current and deferred liability of $16.6 million , related to our performance units. The current liability was recorded in "Accounts payable and other accrued liabilities-other" in the amount of $8.5 million at September 30, 2017. The deferred liability was recorded in “Deferred Credits-other” in the amount of $8.1 million , at September 30, 2017. As of September 30, 2018, there was no liability recorded related to our ongoing performance units. During the fiscal year ended September 30, 2017, we paid $6.7 million in cash to settle performance unit awards. During the fiscal year ended September 30, 2018, we paid an additional $8.5 million in cash to settle performance unit awards that vested before the Merger. There were no such settlements during the three months ended December 31, 2018. Modification Event Upon the Merger with AltaGas, the vesting for the stock-based awards granted in fiscal years 2017 and 2016 was accelerated and the awards were paid in cash, with no additional service required. All performance shares were converted into cash at a value of $88.25 per share. All performance units remained at a value of $1.00 per unit. The TSR Awards were paid at the greater of actual total shareholder return performance or the target award value. The ROE Awards and Dividend Coverage Awards were paid at the target award value. Any dividend equivalents for the performance share awards were also paid in cash. During the fiscal year ended September 30, 2018, we paid $30.0 million in cash to settle the fiscal year 2017 and 2016 awards that were accelerated. The stock-based awards granted in fiscal year 2018 were converted to a fixed cash amount at the target award level, and still require vesting in accordance with the original three-year period, except for certain employees who may have a change in control event and accelerate vesting. All performance shares were converted into cash at a value of $ 88.25 per share. All performance units remained at a value of $1.00 per unit. These awards will be accounted for under ASC Topic 710 for the remaining service period. For the three months ended December 31, 2018, we recognized compensation expense of $1.0 million for the fiscal year 2018 grant. As of December 31, 2018, the total unrecognized compensation expense related to these awards was $2.7 million , which will be recognized ratably through September 30, 2020, adjusted for forfeitures or accelerated vesting as a result of a change in control event. As of December 31, 2018 and September 30, 2018, we recorded a deferred liability of $3.7 million and $ 3.1 million , respectively, related to the grant in “Deferred Credits-other” and a current liability of $2.9 million and $2.2 million , respectively, in "Accounts payable and other accrued liabilities-other". Stock Grants to Directors Prior to the Merger with AltaGas, non-employee directors received a portion of their annual retainer fee in the form of WGL common stock through the Directors’ Stock Compensation Plan. Up to 270,000 shares of common stock were available under the plan. Shares granted to directors were approximately 9,000 , 10,000 and 13,000 for the fiscal years ended September 30, 2018, 2017 and 2016 , respectively. For those years, the weighted average fair value of the stock on the grant dates was $85.84 , $76.28 , and $62.99 , respectively. Shares awarded to the participants; (i) vest immediately and cannot be forfeited; (ii) may be sold or transferred (subject to WGL's stock ownership guidelines) and (iii) have voting and dividend rights. For each of the fiscal years ended September 30, 2018, 2017 and 2016 , WGL recognized stock-based compensation expense related to stock grants of $0.8 million . No new common stock awards will be granted to directors.

Environmental Matters

Environmental Matters	3 Months Ended
	Dec. 31, 2018
Environmental Remediation Obligations [Abstract]
Environmental Matters	ENVIRONMENTAL MATTERS We are subject to federal, state and local laws and regulations related to environmental matters. These laws and regulations may require expenditures over a long-time frame to control environmental effects. Almost all of the environmental liabilities we have recorded are for costs expected to be incurred to remediate sites where we or a predecessor affiliate operated MGPs. Estimates of liabilities for environmental response costs are difficult to determine with precision because of the various factors that can affect their ultimate level. These factors include, but are not limited to, the following: • the complexity of the site; • changes in environmental laws and regulations at the federal, state and local levels; • the number of regulatory agencies or other parties involved; • new technology that renders previous technology obsolete or experience with existing technology that proves ineffective; • the level of remediation required; and • variations between the estimated and actual period of time that must be dedicated to respond to an environmentally-contaminated site. Washington Gas has identified up to ten sites where it or its predecessors may have operated MGPs. Washington Gas last used any such plant in 1984. In connection with these operations, we are aware that coal tar and certain other by-products of the gas manufacturing process are present at or near some former sites and may be present at others. At December 31, 2018 , September 30, 2018 and September 30, 2017 , Washington Gas reported a liability of $11.3 million , $ 10.2 million and $ 7.7 million , respectively, on an undiscounted basis related to future environmental response costs. These estimates principally include the minimum liabilities associated with a range of environmental response costs expected to be incurred. At December 31, 2018 , September 30, 2018 and September 30, 2017 , Washington Gas estimated the maximum liability associated with all of its sites to be approximately $29.4 million , $ 27.3 million and $ 24.0 million , respectively. The estimates were determined by Washington Gas’ environmental experts, based on experience in remediating MGP sites and advice from legal counsel and environmental consultants. The variation between the recorded and estimated maximum liability primarily results from differences in the number of years that will be required to perform environmental response processes and the extent of remediation that may be required. Washington Gas is currently remediating its East Station property, which is adjacent to the Anacostia River, including ground water pump and treat, tar recovery, soil encapsulation and other treatment. Washington Gas is conducting a remedial investigation and feasibility study under a 2012 consent decree with the District of Columbia and the federal government and additional remediation may be required. In addition, manufactured gas waste was discovered at an adjoining property , a parcel of land adjacent to East Station. Washington Gas has agreed to work with the owners of the adjoining property to perform a site investigation, ground water sampling, and report on the contamination at the site pursuant to oversight by DOEE. Washington Gas received a letter in February 2016 from the District of Columbia and National Park Service regarding the Anacostia River Sediment Project, indicating that the District of Columbia is conducting a separate remedial investigation and feasibility study of the Anacostia River to determine if and what cleanup measures may be required and to prepare a natural resource damage assessment. The sediment project draft remedial investigation report issued on March 30, 2018 identifies East Station as one of seventeen potential environmental cleanup sites. We are not able to estimate the total amount of potential damages or timing associated with the District of Columbia's environmental investigation on the Anacostia River at this time. While an allocation method has not been established, Washington Gas has accrued an amount for study costs based on a potential range of estimates. Regulatory orders issued by the PSC of MD allow Washington Gas to recover the costs associated with the sites applicable to Maryland over the period ending in 2025. Rate orders issued by the PSC of DC allow Washington Gas a three -year recovery of prudently incurred environmental response costs and allow Washington Gas to defer additional costs incurred between rate cases. Regulatory orders from the SCC of VA have generally allowed the recovery of prudent environmental remediation costs to the extent they were included in the underlying financial data supporting an application for rate change. At December 31, 2018 , September 30, 2018 and September 30, 2017 , Washington Gas reported a regulatory asset of $5.8 million , $ 5.0 million and $ 2.5 million , respectively, for the portion of environmental response costs that are expected to be recoverable in future rates.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES OPERATING LEASES Minimum future rental payments under operating leases over the next five calendar years and thereafter are as follows: Minimum Payments Under Operating Leases (a) (In millions) 2019 $ 3.0 2020 5.7 2021 5.3 2022 5.3 2023 5.4 Thereafter 50.8 Total $ 75.5 (a) During the year 2018, we moved our headquarter to the office located at 1000 Maine Ave., S.W. Washington, D.C. The operating lease of the previous office located at 101 Constitution Ave., N.W. Washington, D.C. ended in August 2018. Rent expense totaled $0.6 million for the three months ended December 31, 2018 and $5.8 million , $5.3 million and $5.4 million in fiscal years ended September 30, 2018, 2017 and 2016 , respectively. Natural Gas Contracts—Minimum Commitments At December 31, 2018 , Washington Gas had service agreements with four pipeline companies that provide direct service for firm transportation and/or storage services. These agreements, which have expiration dates ranging from calendar years 2020 to 2044 , require Washington Gas to pay fixed charges each month. Additionally, Washington Gas had agreements for other pipeline and peaking services with expiration dates ranging from 2020 to 2027. These agreements were entered into based on current estimates of growth of the Washington Gas system, together with other factors, such as current expectations of the timing and extent of unbundling initiatives in the Washington Gas service territory. The following table summarizes the minimum contractual payments that Washington Gas will make under its pipeline transportation, storage and peaking contracts, as well as minimum contractual payments to purchase natural gas at prices based on market conditions during the next five calendar years and thereafter. Washington Gas Contract Minimums (In millions) Pipeline Contracts (a) Gas Purchase Commitments (b) 2019 $ 373.1 $ 459.2 2020 374.1 384.8 2021 366.3 362.0 2022 362.6 353.9 2023 362.1 339.4 Thereafter 1,209.6 2,695.7 Total $ 3,047.8 $ 4,595.0 (a) Represents minimum payments for natural gas transportation, storage and peaking contracts that have expiration dates through calendar year 2044 . (b) Includes known and reasonably likely commitments to purchase natural gas. Cost estimates are based on forward market prices at December 31, 2018 . When a customer selects a third-party marketer to provide supply, Washington Gas generally assigns pipeline and storage capacity to unregulated third-party marketers to deliver gas to Washington Gas’ city gate. In order to provide the gas commodity to customers who do not select an unregulated third-party marketer, Washington Gas has a commodity acquisition plan to acquire the natural gas supply to serve the customers. To the extent these commitments are to serve its customers, Washington Gas has rate provisions in each of its jurisdictions that would allow it to continue to recover these commitments in rates. Washington Gas also actively manages its supply portfolio to ensure its sales and supply obligations remain balanced. This reduces the likelihood that the contracted supply commitments would exceed supply obligations. However, to the extent Washington Gas were to determine that changes in regulation would cause it to discontinue recovery of these costs in rates, Washington Gas would be required to charge these costs to expense without any corresponding revenue recovery. If this occurred, depending upon the timing of the occurrence, the related impact on our financial position, results of operations and cash flows would likely be significant. Silver Spring, Maryland Incident Washington Gas continues to support the investigation by the NTSB into the August 10, 2016 explosion and fire at an apartment complex on Arliss Street in Silver Spring, Maryland, the cause of which has not been determined. The NTSB has scheduled a board meeting, open to the public, on April 23, 2019, “to determine the probable cause” of the incident. A total of 40 civil actions related to the incident have been filed against WGL and Washington Gas in the Circuit Court for Montgomery County, Maryland. All of these suits seek unspecified damages for personal injury and/or property damage. The one action seeking class action status has been amended to assert property damage and loss of use claims. The trial date for the hearings has been scheduled for December 2, 2019. We maintain excess liability insurance coverage from highly-rated insurers, subject to a nominal self-insured retention. We believe that this coverage will be sufficient to cover any significant liability that may result from this incident. Management is unable to determine a range of potential losses that are reasonably possible of occurring and therefore we have not recorded a reserve associated with this incident. Washington Gas was invited by the NTSB to be a party to the investigation and in that capacity, has worked closely with the NTSB to help determine the cause of this incident. Regulatory Contingencies Certain legal and administrative proceedings incidental to our business, including regulatory contingencies, involve Washington Gas. In our opinion, we have recorded an adequate provision for probable losses or refunds to customers for regulatory contingencies related to these proceedings. Application for Approval of Reduction of Distribution Rates On January 12, 2018, Washington Gas filed applications to reduce customer rates in Maryland, Virginia, and the District of Columbia to reflect the impact of the Tax Act, including both the impact of the re-measurement of deferred tax assets and liabilities and reduction of the federal tax rate to 21%. Washington Gas began tracking the impact of the Tax Act on revenue requirements beginning January 1, 2018, recording all impacts to regulatory assets and liabilities. In Maryland, the PSC of MD approved the application for an annual reduction in Washington Gas’ distribution rates of $14.8 million , effective for bills rendered on or after February 1, 2018. In Virginia, the application was dismissed on March 15, 2018 and Washington Gas filed a new general rate case in July 2018 incorporating the effects of the Tax Act. On June 29, 2018, the PSC of DC approved the settlement agreement, reflecting an annual reduction in Washington Gas’ distribution rates of $8.3 million , effective for service rendered on or after July 1, 2018. The settling parties were directed to file a joint proposal, by August 1, 2018, depicting the regulatory liability balance for the period January 1, 2018 through June 30, 2018, which were refunded to customers. Washington Gas has recorded regulatory liabilities, representing the amounts owed to customers for reduced rates between January 1, 2018 and December 31, 2018 of $19.2 million for Virginia. Please refer to Note 8— Income taxes for more information. Virginia Jurisdiction Virginia Rate Case. On July 31, 2018, Washington Gas filed an application with the SCC of VA to increase its base rates for natural gas service by $37.6 million , which includes $14.7 million of revenue associated with natural gas pipeline replacement initiatives previously approved by the Commission and paid by customers through a monthly rider. Additionally, the requested revenue amount reflects a $16.3 million reduction for lower tax expense due to the implementation of the Tax Act and excludes any costs related to the acquisition of Washington Gas by AltaGas on July 6, 2018. At December 31, 2018, Washington Gas had accrued $19.2 million related to the Tax Act. Refer to Note 8- Income Taxes for a discussion of regulatory liabilities we have established related to tax reform and Note 18- Merger with AltaGas, Ltd. for a discussion of the merger. On August 23, 2018, the Commission issued an Order setting a procedural schedule and appointing a Hearing Examiner. Interim rates became effective, subject to refund, for usage in the January 2019 billing cycle. Financial Guarantees At December 31, 2018, there were no guarantees to external parties. MERGER RELATED COMMITMENTS For a discussion of merger related commitments, refer to Note 18 - Merger with AltaGas Ltd. of the Notes to Financial Statements.

Derivative and Weather Related

Derivative and Weather Related Instruments	3 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative and Weather-Related Instruments	DERIVATIVES DERIVATIVE INSTRUMENTS Washington Gas enters into contracts that qualify as derivative instruments and are accounted for under ASC Topic 815. These derivative instruments are recorded at fair value on our balance sheets and Washington Gas does not currently designate any derivatives as hedges under ASC Topic 815. Washington Gas’ derivative instruments relate to: (i) Washington Gas’ asset optimization program; (ii) managing price risk associated with the purchase of gas to serve utility customers and (iii) managing interest rate risk. Asset Optimization. Washington Gas optimizes the value of its long-term natural gas transportation and storage capacity resources during periods when these resources are not being used to physically serve utility customers. Specifically, Washington Gas utilizes its transportation capacity assets to benefit from favorable natural gas prices between different geographic locations and utilizes its storage capacity assets to benefit from favorable natural gas prices between different time periods. As part of this asset optimization program, Washington Gas enters into physical and financial derivative transactions in the form of forward, futures and option contracts with the primary objective of securing operating margins that Washington Gas will ultimately realize. The derivative transactions entered into under this program are subject to mark-to-market accounting treatment under ASC Topic 820. Regulatory sharing mechanisms provide for the annual realized profit from these transactions to be shared between Washington Gas' shareholders and customers; therefore, changes in fair value are recorded through earnings, or as regulatory assets or liabilities to the extent that it is probable that realized gains and losses associated with these derivative transactions will be included in the rates charged to customers when they are realized. Unrealized gains and losses recorded to earnings may cause significant period-to-period volatility; this volatility does not change the operating margins that Washington Gas expects to ultimately realize from these transactions through the use of its storage and transportation capacity resources. All physically and financially settled contracts under our asset optimization program are reported on a net basis in the statements of income in “Utility cost of gas.” Total net margins recorded to “Utility cost of gas” after sharing and management fees associated with all asset optimization transactions for the three months ended December 31, 2018 was a net gain of $1.1 million including an unrealized loss of $4.2 million . During the fiscal year ended September 30, 2018, we recorded a net gain of $34.3 million including an unrealized gain of $10.4 million . During the fiscal year ended September 30, 2017 , we recorded a net gain of $82.9 million including an unrealized gain of $49.3 million . During the fiscal year ended September 30, 2016 , we recorded a net gain of $43.8 million including an unrealized gain of $12.0 million . Managing Price Risk. To manage price risk associated with acquiring natural gas supply for utility customers, Washington Gas enters into physical and financial derivative transactions in the form of forward, option and other contracts, as authorized by its regulators. Any gains and losses associated with these derivatives are recorded as regulatory liabilities or assets, respectively, to reflect the rate treatment for these economic hedging activities. Managing Interest-Rate Risk. Washington Gas may utilize derivative instruments that are designed to minimize the risk of interest-rate volatility associated with planned issuances of debt securities. Any gains and losses associated with these types of derivatives are recorded as regulatory liabilities or assets, respectively, and amortized in accordance with regulatory requirements, typically over the life of the related debt. Operations The following table presents the balance sheet classification for all derivative instruments as of December 31, 2018 , September 30, 2018 and September 30, 2017 . Absolute Notional Amounts of Open Positions on Derivative Instruments Derivative transactions Notional Amounts December 31, 2018 December 31, 2018 September 30, 2018 September 30, 2017 Natural Gas (In millions of therms) Asset optimization & trading 13,051.0 13,580.0 11,223.0 Other risk-management activities 1,072.0 1,066.0 1,181.0 The following table presents the balance sheet classification for all derivative instruments as of December 31, 2018 , September 2018 and September 2017 . Balance Sheet Classification of Derivative Instruments (b) (In millions) As of December 31, 2018 Gross Gross Netting of Total (a) Current Assets—Derivatives $ 25.7 $ (6.2 ) $ — $ 19.5 Deferred Charges and Other Assets—Derivatives 11.3 — — 11.3 Current Liabilities—Derivatives 1.1 (21.4 ) (20.3 ) Deferred Credits—Derivatives — (116.8 ) — (116.8 ) Total $ 38.1 $ (144.4 ) $ — $ (106.3 ) As of September 30, 2018 Current Assets—Derivatives $ 17.8 $ (0.4 ) $ — $ 17.4 Deferred Charges and Other Assets—Derivatives 8.7 — — 8.7 Current Liabilities—Derivatives 2.6 (20.2 ) 2.8 (14.8 ) Deferred Credits—Derivatives (1.6 ) (102.6 ) — (104.2 ) Total $ 27.5 $ (123.2 ) $ 2.8 $ (92.9 ) As of September 30, 2017 Current Assets—Derivatives $ 7.5 $ (2.4 ) $ — $ 5.1 Deferred Charges and Other Assets—Derivatives 16.5 (0.3 ) — 16.2 Current Liabilities—Derivatives — (30.3 ) — (30.3 ) Deferred Credits—Derivatives — (112.3 ) — (112.3 ) Total $ 24.0 $ (145.3 ) $ — $ (121.3 ) (a) Washington Gas has elected to offset the fair value of recognized derivative instruments against the right to reclaim or the obligation to return collateral for derivative instruments executed under the same master netting arrangement in accordance with ASC Topic 815. All recognized derivative contracts and associated financial collateral subject to a master netting arrangement or similar that is eligible for offset under ASC Topic 815 have been presented net in the balance sheet. (b) Washington Gas did not have derivative instruments outstanding that were designated as hedging instruments at December 31, 2018 , September 30, 2018, or September 30, 2017 . The following tables present all gains and losses associated with derivative instruments for the three months ended December 31, 2018 , and the fiscal years ended September 30, 2018, 2017 and 2016 . Washington Gas Light Company Gains and (Losses) on Derivative Instruments (In millions) Three Months Ended December 31, Fiscal Year Ended September 30, 2018 2018 2017 2016 Recorded to income Utility cost of gas (3.2 ) (2.1 ) 50.1 12.1 Recorded to regulatory assets Gas costs (6.0 ) (7.6 ) 77.2 13.9 Other (a) — — — (7.3 ) Total $ (9.2 ) $ (9.7 ) $ 127.3 $ 18.7 (a) Represents the settlement of Washington Gas' forward starting interest rate swap in September 2016. Collateral Washington Gas utilizes standardized master netting agreements, which facilitate the netting of cash flows into a single net exposure for a given counterparty. As part of these master netting agreements, cash, letters of credit and parent company guarantees may be required to be posted or obtained from counterparties in order to mitigate credit risk related to both derivatives and non-derivative positions. Under Washington Gas' offsetting policy, collateral balances are offset against the related counterparties’ derivative positions to the extent the application would not result in the over-collateralization of those derivative positions on the balance sheet. The table below presents collateral not offset against derivative assets and liabilities at December 31, 2018 , September 30, 2018, and September 30, 2017 , respectively. Collateral Not Offset Against Derivative Assets and Liabilities (In millions) Collateral deposits posted with counterparties Cash collateral held representing an obligation December 31, 2018 $ 7.4 $ 0.2 September 30, 2018 10.6 2.7 September 30, 2017 $ 3.7 $ 0.1 Any collateral posted that is not offset against derivative assets and liabilities is included in “Other prepayments” in the accompanying balance sheets. Collateral received and not offset against derivative assets and liabilities is included in “Customer deposits and advance payments” in the accompanying balance sheets. Certain derivative instruments of Washington Gas contain contract provisions that require collateral to be posted if the credit rating of Washington Gas falls below certain levels or if counterparty exposure to Washington Gas exceeds a certain level (credit-related contingent features) . At December 31, 2018 , September 30, 3018, and September 30, 2017 , Washington Gas was not required to post collateral related to a derivative liability that contained a credit-related contingent feature. The following table shows the aggregate fair value of all derivative instruments with credit-related contingent features that are in a liability position, as well as the maximum amount of collateral that would be required if the most intrusive credit-risk-related contingent features underlying these agreements were triggered on December 31, 2018, September 30, 2018 and September 30, 2017, respectively. Potential Collateral Requirements for Derivative Liabilities with Credit-Risk-Contingent Features (In millions) December 31, 2018 Derivative liabilities with credit-risk-contingent features $ 1.1 Maximum potential collateral requirements 1.0 September 30, 2018 Derivative liabilities with credit-risk-contingent features $ 0.4 Maximum potential collateral requirements $ 0.4 September 30, 2017 Derivative liabilities with credit-risk-contingent features $ 2.8 Maximum potential collateral requirements 2.8 We do not enter into derivative contracts for speculative purposes. Concentration of Credit Risk We are exposed to credit risk from derivative instruments with wholesale counterparties, which is represented by the fair value of these instruments at the reporting date. We actively monitor and work to minimize counterparty concentration risk through various practices. At December 31, 2018 , three counterparties each represented over 10% of Washington Gas’ credit exposure to wholesale derivative counterparties for a total credit risk of $41.6 million .

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Recurring Basis We measure the fair value of our financial assets and liabilities using a combination of the income and market approaches in accordance with ASC Topic 820. These financial assets and liabilities primarily consist of derivatives recorded on our balance sheet under ASC Topic 815 and short-term investments, commercial paper and long-term debt outstanding required to be disclosed at fair value. Under ASC Topic 820, fair value is defined as the exit price, representing the amount that would be received in the sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. To value our financial instruments, we use market data or assumptions that market participants would use, including assumptions about credit risk (both our own credit risk and the counterparty’s credit risk) and the risks inherent in the inputs to valuation. We enter into derivative contracts in the futures and over-the-counter (OTC) wholesale and retail markets. These markets are the principal markets for the respective wholesale and retail contracts. Our relevant market participants are our existing counterparties and others who have participated in energy transactions at our delivery points. These participants have access to the same market data as Washington Gas. Valuations are generally based on pricing service data or indicative broker quotes depending on the market location. We measure the net credit exposure at the counterparty level where the right to set-off exists. The net exposure is determined using the mark-to-market exposure adjusted for collateral, letters of credit and parent guarantees. We use published default rates from Standard & Poor’s Ratings Services and Moody’s Investors Service as inputs for determining credit adjustments. ASC Topic 820 establishes a fair value hierarchy that prioritizes the inputs used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. The three levels of the fair value hierarchy under ASC Topic 820 are described below: Level 1. Level 1 of the fair value hierarchy consists of assets or liabilities that are valued using observable inputs based upon unadjusted quoted prices in active markets for identical assets or liabilities at the reporting date. Washington Gas did not have any Level 1 derivatives at December 31, 2018 , September 30, 2018 and September 30, 2017 . Level 2. Level 2 of the fair value hierarchy consists of assets or liabilities that are valued using directly or indirectly observable inputs either corroborated with market data or based on exchange traded market data. Level 2 includes fair values based on industry-standard valuation techniques that consider various assumptions: (i) quoted forward prices, including the use of mid-market pricing within a bid/ask spread; (ii) discount rates; (iii) implied volatility and (iv) other economic factors. Substantially all of these assumptions are observable throughout the full term of the instrument, can be derived from observable data or are supported by observable levels at which transactions are executed in the relevant market. At December 31, 2018 , September 30, 2018 and September 30, 2017 , Level 2 financial assets and liabilities included energy-related physical and financial derivative transactions such as forward, option and other contracts for deliveries at active market locations, as well as our interest rate swaps. Level 3. Level 3 of the fair value hierarchy consists of assets or liabilities that are valued using significant unobservable inputs at the reporting date. These unobservable assumptions reflect our assumptions about estimates that market participants would use in pricing the asset or liability, including natural gas basis prices and annualized volatilities of natural gas prices. A significant change to any one of these inputs in isolation could result in a significant upward or downward fluctuation in the fair value measurement. These inputs may be used with industry standard valuation methodologies that result in our best estimate of fair value for the assets or liabilities at the reporting date. Our Risk Analysis and Mitigation (RA&M) Group determines the valuation policies and procedures. The RA&M Group reports to Washington Gas' Chief Financial Officer. In accordance with Washington Gas valuation policy, we may utilize a variety of valuation methodologies to determine the fair value of Level 3 derivative contracts, including internally developed valuation inputs and pricing models. The prices used in our valuations are corroborated using multiple pricing sources, and we periodically conduct assessments to determine whether each valuation model is appropriate for its intended purpose. The RA&M Group also evaluates changes in fair value measurements on a daily basis. At December 31, 2018 , September 30, 2018 and September 30, 2017 , Level 3 derivative assets and liabilities included: (i) physical contracts valued at illiquid market locations with no observable market data; (ii) long-dated positions where observable pricing is not available over the majority of the life of the contract; (iii) contracts valued using historical spot price volatility assumptions and (iv) valuations using indicative broker quotes for inactive market locations. The following tables set forth financial instruments recorded at fair value as of December 31, 2018 , September 30, 2018 and September 30, 2017 , respectively. A financial instrument’s classification within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement requires judgment and may affect the valuation of fair value assets and liabilities and their placement within the fair value hierarchy. Fair Value Measurements Under the Fair Value Hierarchy (In millions) Level 1 Level 2 Level 3 Total At December 31, 2018 Assets Natural gas related derivatives $ — $ 9.8 $ 28.3 $ 38.1 Total Assets $ — $ 9.8 $ 28.3 $ 38.1 Liabilities Natural gas related derivatives $ — $ (9.5 ) $ (134.9 ) $ (144.4 ) Total Liabilities $ — $ (9.5 ) $ (134.9 ) $ (144.4 ) At September 30, 2018 Assets Natural gas related derivatives $ — $ 3.9 $ 23.6 $ 27.5 Total Assets $ — $ 3.9 $ 23.6 $ 27.5 Liabilities Natural gas related derivatives $ — $ (5.5 ) $ (117.7 ) $ (123.2 ) Total Liabilities $ — $ (5.5 ) $ (117.7 ) $ (123.2 ) At September 30, 2017 Assets Natural gas related derivatives $ — $ 7.0 $ 17.0 $ 24.0 Total Assets $ — $ 7.0 $ 17.0 $ 24.0 Liabilities Natural gas related derivatives $ — $ (5.7 ) $ (139.6 ) $ (145.3 ) Total Liabilities $ — $ (5.7 ) $ (139.6 ) $ (145.3 ) The following table includes quantitative information about the significant unobservable inputs used in the fair value measurement of our Level 3 financial instruments and the respective fair values of the net derivative asset and liability positions, by contract type, as of December 31, 2018 , September 30, 2018 and September 30, 2017 . Quantitative Information about Level 3 Fair Value Measurements (In millions) Net Fair Value Valuation Techniques Unobservable Inputs Range Natural gas related derivatives ($106.6) Discounted Cash Flow Natural Gas Basis Price (per dekatherm) ($1.028)-$5.34 Net Fair Value Natural gas related derivatives ($94.1) Discounted Cash Flow Natural Gas Basis Price ($1.003) - $3.886 Net Fair Value Natural gas related derivatives ($122.6) Discounted Cash Flow Natural Gas Basis Price (per dekatherm) ($1.928) - $2.805 The following tables are a summary of the changes in the fair value of our derivative instruments that are measured at net fair value on a recurring basis in accordance with ASC Topic 820 using significant Level 3 inputs during the three months ended December 31, 2018 , and the fiscal years ended September 30, 2018 and September 30, 2017 , respectively. Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs (In millions) Total - Natural Gas Three Months Ended December 31, 2018 Balance at October 1, 2018 $ (94.1 ) Realized and unrealized gains (losses) Recorded to income (4.4 ) Recorded to regulatory assets—gas costs (5.8 ) Transfers into Level 3 — Transfers out of Level 3 — Settlements (2.3 ) Balance at December 31, 2018 $ (106.6 ) Fiscal Year Ended September 30, 2018 Balance at October 1, 2017 $ (122.6 ) Balance at Realized and unrealized gains (losses) — Recorded to income (4.5 ) Recorded to regulatory assets—gas costs (10.0 ) Transfers into Level 3 (6.9 ) Transfers out of Level 3 8.9 Settlements 41.0 Balance at September 30, 2018 $ (94.1 ) Fiscal Year Ended September 30, 2017 Balance at October 1, 2016 $ (251.6 ) Realized and unrealized gains (losses) Recorded to income 44.2 Recorded to regulatory assets—gas costs 69.7 Transfers into Level 3 (0.4 ) Transfers out of Level 3 (0.4 ) Settlements 15.9 Balance at September 30, 2017 $ (122.6 ) Transfers between different levels of the fair value hierarchy may occur based on fluctuations in the valuation inputs and on the level of observable inputs used to value the instruments from period to period. It is our policy to show both transfers into and out of the different levels of the fair value hierarchy at the fair value as of the beginning of the period. Transfers out of Level 3 during the three months ended December 31, 2018 , and fiscal years ended September 30, 2018 and September 30, 2017 were due to valuations that experienced an increase in observable market inputs. Transfers into Level 3 during the three months ended December 31, 2018 , and fiscal years ended September 30, 2018 and September 30, 2017 were due to an increase in unobservable market inputs, primarily pricing points. The table below sets forth the line items on the statements of income to which amounts are recorded for the three months ended December 31, 2018 , and the fiscal years ending September 30, 2018, 2017 and 2016 , respectively, related to fair value measurements using significant Level 3 inputs. Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements (In millions) Total - Natural Gas Fiscal Year Ended December 31, 2018 Utility cost of gas $(4.4) Fiscal Year Ended September 30, 2018 Utility cost of gas $(4.5) Fiscal Year Ended September 30, 2017 Utility cost of gas $44.2 Fiscal Year Ended September 30, 2016 Utility cost of gas $4.0 Unrealized gains (losses) attributable to derivative assets and liabilities measured using significant Level 3 inputs were recorded as follows for the fiscal years ended December 31, 2018 , and September 30, 2018, 2017 and 2016 , respectively: Unrealized Gains (Losses) Recorded for Level 3 Measurements (In millions) Total - Natural Gas Fiscal Year Ended December 31, 2018 Recorded to income Utility cost of gas $(4.0) Recorded to regulatory assets—gas costs (5.3) Total $(9.3) Fiscal Year Ended September 30, 2018 Recorded to income Utility cost of gas $2.3 Recorded to regulatory assets—gas costs 0.2 Total $2.5 Fiscal Year Ended September 30, 2017 Recorded to income Utility cost of gas $31.0 Recorded to regulatory assets—gas costs 51.0 Total $82.0 Fiscal Year Ended September 30, 2016 Recorded to income Utility cost of gas $0.3 Recorded to regulatory assets—gas costs (2.6) Total $(2.3) The following tables presents the carrying amounts recorded at amortized cost on Washington Gas' balance sheets and estimated fair values of our financial instruments at December 31, 2018 , September 30, 2018 and September 30, 2017 . Washington Gas Light Company Fair Value of Financial Instruments December 31, 2018 September 30, 2018 September 30, 2017 (In millions) Carrying Amount Fair Value Carrying Amount Fair Value Carrying Amount Fair Value Money market funds (a) $ 69.7 $ 69.7 $ 67.3 $ 67.3 $ 4.8 $ 4.8 Commercial paper (b) $ 296.0 $ 296.0 $ 95.0 $ 95.0 $ 123.0 $ 123.0 Project financing (b) $ 15.5 $ 15.5 $ 68.5 $ 68.5 $ 43.8 $ 43.8 Current Maturities of Long-term Debt $ 50.0 $ 50.0 $ 50.0 $ 50.0 $ — $ — Long-term debt (c) $ 1,035.0 $ 1,096.3 $ 1,084.9 $ 1,120.2 $ 1,134.5 $ 1,271.0 (a) The balance as of December 31, 2018 includes $4.4 million money market funds located in "Cash and cash equivalents", $ 20.2 million rabbi trust investment located in "Current Assets-Other", and $ 45.1 million rabbi trust investments located in "Deferred Charges and Other Assets-Other" of the accompanying balance sheets; The balance as of September 30, 2018 includes $2.3 million money market funds located in "Cash and cash equivalents", $ 20.2 million rabbi trust investment located in "Current Assets-Other" and $44.8 million rabbi trust investments located in "Deferred Charges and Other Assets-Other" ; The balance as of September 2017 is located in "Cash and cash equivalents". The amounts in cash and cash equivalent may be offset by outstanding checks. (b) Balance is located in "Notes payable and project financing" in the accompanying balance sheets. (c) Includes adjustments for current maturities and unamortized discounts, as applicable. Our money market funds are Level 1 valuations and their carrying amount approximates fair value. The maturity of our commercial paper outstanding at both December 31, 2018 , September 30, 2018 and September 30, 2017 is under 30 days. Due to the short term nature of these notes, the carrying cost of our commercial paper approximates fair value using Level 2 inputs. Due to the nature of our project financing arrangements, the carrying cost approximates fair value using Level 2 inputs. Due to the short term nature of current maturities of long-term debt, the carrying cost approximates fair value using level 2 inputs, Washington Gas’ long-term debt is not actively traded. The fair value of long-term debt was estimated based on valuation techniques when observable market data is not available. Our long-term debt fair value measurement is classified as Level 3. Non Recurring Basis Washington Gas does not have financial instruments recorded at fair value on non-recurring basis as of December 31, 2018, September 30, 2018 and September 30, 2017.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	RELATED PARTY TRANSACTIONS Related Party Transactions with AltaGas LTD. As a subsidiary of AltaGas and effective with the close of the Merger on July 6, 2018, Washington Gas is charged a proportionate share of corporate governance and other shared services costs from AltaGas, primarily related to human resources, employee benefits, finance, legal, accounting, tax, information technology services, and office services. AltaGas charges Washington Gas for the total shared service costs and Washington Gas in turn allocates a portion of the costs to WGL’s other subsidiaries at the lower of cost or market. Washington Gas records a payable of the total shared service costs allocated to all WGL's subsidiaries in "Payable to associated companies" and a receivable of the shared service costs allocated to WGL’s other subsidiaries in “Receivables from associated companies” on the balance sheet. As of December 31, 2018, Washington Gas recorded a receivable from associated companies of $ 0.6 million on the balance sheet related to the shared service costs allocated to WGL's subsidiaries, and $ 4.5 million net expenses included in "Operation and maintenance" of the statements of income for the three months ended December 31, 2018, reflecting the shared service cost allocated to Washington Gas. There is no payable balance related to the shared service cost as of December 31, 2018. As of September 30, 2018, Washington Gas recorded a payable of $ 5.1 million and receivable of $ 1.1 million in the balance sheet, and $ 4.0 million net expenses for the fiscal year ended September 30, 2018. We did not have related transactions with AltaGas during the fiscal year 2017. Effective upon the approval by SCC of Virginia on December 17, 2018, Washington Gas will provide accounting, legal, tax and other administrative and general support to various AltaGas entities. The services will begin in January 2019. Related Party Transactions with Other Affiliates Washington Gas provides accounting, treasury, legal and other administrative and general support to WGL's subsidiaries, and files consolidated tax returns that include affiliated taxable transactions. Washington Gas bills its WGL's subsidiaries in accordance with regulatory requirements for the actual cost of providing these services, which approximates their market value. To the extent such billings are outstanding, they are reflected in “Receivables from associated companies” on Washington Gas’ balance sheets. Washington Gas assigns or allocates these costs directly to its affiliates and, therefore, does not recognize revenues or expenses associated with providing these services. Washington Gas believes that allocations based on broad measures of business activity are appropriate for allocating expenses resulting from common services. Affiliate entities are allocated a portion of common services based on a formula driven by appropriate indicators of activity, as approved by management. In connection with billing for unregulated third-party marketers, including WGL Energy Services and with other miscellaneous billing processes, Washington Gas collects cash on behalf of affiliates and transfers the cash in a reasonable time period. Cash collected by Washington Gas on behalf of its affiliates but not yet transferred is recorded in “Payables to associated companies” on Washington Gas’ balance sheets. Washington Gas previously obtained third-party project financing on behalf of the federal government to provide funds during the construction of certain energy management services projects entered into under Washington Gas' area-wide contract. In December 2016, WGL Energy Systems entered into an agreement to obtain third-party financing and receive funds directly from the third-party lender during the construction period associated with the related energy management service projects. Washington Gas continued to record a receivable in "Unbilled revenues" representing the government’s obligation and recorded an account payable to WGL Energy Systems in "Payable to associated companies" for the construction work performed for the same amount. Refer to Note 5- Short Term Debt of the Notes to Financial Statements for further discussions of the project financing. As the subsidiary of WGL, Hampshire owns full and partial interests in underground natural gas storage facilities, including pipeline delivery facilities located in and around Hampshire County, West Virginia, and operates those facilities to serve Washington Gas, which purchases all of the storage services of Hampshire. Washington Gas includes the cost of these services in the bills sent to its customers and records the cost of the services in "Operation and maintenance" in its statements of income. Hampshire operates under a “pass-through” cost of service-based tariff approved by the FERC and adjusts its billing rates to Washington Gas on a periodic basis to account for changes in its investment in utility plant and associated expenses. During the three months ended December 31, 2018, Washington Gas recorded $ 1.7 million of expenses related to the cost of services provided by Hampshire in Washington Gas' Statements of Income. During the fiscal years ended September 30, 2018, 2017 and 2016, Washington Gas recorded $ 6.9 million , $ 6.8 million , and $ 6.4 million , respectively, of the expense for the services provided by Hampshire. The outstanding balance not cleared between Washington Gas and Hampshire at the end of the reporting period was recorded in "Receivables from associated companies" of Washington Gas' balance sheet. The following table presents the receivables and payables from associated companies as of December 31, 2018, September 30, 2018 and September 30, 2017. Washington Gas Light Company Receivables / Payables from Associated Companies (In millions) December 31, 2018 September 30, 2018 September 30, 2017 Receivables from associated companies (a) $ 4.2 $ 1.1 $ 32.4 Payables to associated companies (a) $ 95.2 $ 16.4 $ 94.8 (a) The receivables and payables do not include the transactions related to shared service cost billed from AltaGas. Washington Gas provides gas balancing services related to storage, injections, withdrawals and deliveries to all energy marketers participating in the sale of natural gas on an unregulated basis through the customer choice programs that operate in its service territory. These balancing services include the sale of natural gas supply commodities related to various peaking arrangements contractually supplied to Washington Gas and then partially allocated and assigned by Washington Gas to the energy marketers, including WGL Energy Services. Washington Gas records revenues for these balancing services pursuant to tariffs approved by the appropriate regulatory bodies. The following table shows the amounts Washington Gas charged WGL Energy Services for balancing services. Washington Gas - Gas Balancing Service Charges Three Month Ended December 31 Fiscal Years Ended September 30, (In millions) 2018 2018 2017 2016 Gas balancing service charge $ 4.6 $ 18.5 $ 23.6 $ 26.8 As a result of these balancing services, an imbalance is created for volumes of natural gas received by Washington Gas that are not equal to the volumes of natural gas delivered to customers of the energy marketers. Washington Gas recorded receivable from WGL Energy Services of $0.7 million , and payable of $ 1.5 million and $ 1.4 million at December 31, 2018, September 30, 2018 and September 30, 2017, respectively , related to an imbalance in gas volumes. The receivable and payable are recorded in "Account receivable" and "Account payable and other accrued liabilities" on Washington Gas' balance sheet. Refer to Note 1— Accounting Policies of the Notes to Financial Statements for further discussion of these imbalance transactions. Washington Gas participates in a purchase of receivables (POR) program as approved by the PSC of MD, whereby it purchases receivables from participating energy marketers at approved discount rates. In addition, WGL Energy Services participates in POR programs with certain Maryland, District of Columbia and Pennsylvania utilities, whereby it sells its receivables to various utilities, including Washington Gas, at approved discount rates. The receivables purchased by Washington Gas are included in “Accounts receivable” in the accompanying balance sheet. At December 31, 2018 , September 30, 2018 and September 30, 2017 , Washington Gas had balances of $6.4 million , $ 2.8 million and $ 3.2 million , respectively, of purchased receivables from WGL Energy Services. Additionally, Washington Gas expects to implement a program in the District of Columbia to participate in a POR program in January 2019.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	3 Months Ended
	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss)	ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) The following table shows the changes in accumulated other comprehensive income (loss) for Washington Gas by component for the three months ended December 31, 2018 , and the fiscal years ended September 30, 2018 and September 30, 2017 . Changes in Accumulated Other Comprehensive Income (Loss) by Component Three Months Ended December 31, Fiscal Year Ended September 30, (In thousands) 2018 2018 2017 Beginning Balance $ (1,830 ) $ (4,522 ) $ (7,830 ) Change in prior service cost (a) (226 ) (675 ) (767 ) Amortization of actuarial gain (loss) (a) (6,246 ) 6,324 6,232 Current-period other comprehensive income (loss) (6,472 ) 5,649 5,465 Income tax expense (benefit) related to other comprehensive income (loss) (1,675 ) 2,957 2,157 Ending Balance $ (6,627 ) $ (1,830 ) $ (4,522 ) (a) These accumulated other comprehensive income (loss) components are included in the computation of net periodic benefit cost. Refer to Note 9—Pension and other post-retirement benefit plans for additional details.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	3 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Information [Abstract]
Supplemental Cash Flow Information	SUPPLEMENTAL CASH FLOW INFORMATION The following table details the changes in operating assets and liabilities from operating activities, cash payments that have been included in the determination of earnings and non-cash investing and financing activities: Three Months Ended December 31, Fiscal Year Ended September 30, 2018 2018 2017 2016 (In thousands) CHANGES IN OPERATING ASSETS AND LIABILITIES Accounts receivable and unbilled revenues $ (222,098 ) $ (13,557 ) $ (107,195 ) $ (67,681 ) Receivables from associated companies (1,874 ) 30,135 (18,563 ) (10,623 ) Gas costs and other regulatory assets/liabilities—net 40,028 27,994 3,430 (31,075 ) Storage gas (2,550 ) (8,626 ) (10,280 ) 12,016 Prepaid taxes (9,461 ) 5,618 (6,524 ) 13,539 Accounts payable and other accrued liabilities 61,029 18,378 17,921 34,261 Payables to associated companies 20,662 (73,296 ) 29,074 (2,853 ) Customer deposits and advance payments (29,288 ) 19,464 (16,742 ) (7,514 ) Accrued taxes 1,024 14,619 (4,831 ) 5,980 Other current assets (28 ) (14,605 ) (4,123 ) 3,912 Other current liabilities (121 ) 154 280 (1,318 ) Deferred gas costs—net (51,936 ) (8,306 ) 2,467 (5,104 ) Deferred assets—other 483 (5,895 ) (15,088 ) (22,057 ) Deferred liabilities—other (7,072 ) (21,499 ) (4,667 ) (56,865 ) Pension and other post-retirement benefits (638 ) (14,521 ) (9,806 ) (10,251 ) Other—net — 893 3,409 2,107 Changes in operating assets and liabilities $ (201,840 ) $ (43,050 ) $ (141,238 ) $ (143,526 ) SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION Income taxes paid (refunded)—net $ 3,782 $ (2,983 ) $ — $ (19,004 ) Interest paid $ 4,982 $ 57,036 $ 50,539 $ 40,972 SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING ACTIVITIES: Extinguishment of project debt financing $ (53,018 ) $ (28,312 ) $ (27,927 ) $ — Capital expenditure accruals included in accounts payable and other accrued liabilities $ 33,245 $ 53,367 $ 37,049 $ 43,687 The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within Washington Gas’ balance sheets that sums to the total of such amounts shown on the statements of cash flows. (in thousands) December 31, 2018 September 30, 2018 September 30, 2017 September 30, 2016 Cash and cash equivalents $ 6,082 $ 1 $ 1 $ 1 Restricted cash included in Current assets-Other $ 20,207 $ 20,207 $ — $ — Restricted cash included in Deferred Charges and Other Assets-Other $ 45,134 $ 44,775 $ — $ — Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 71,423 $ 64,983 $ 1 $ 1 Restricted cash included in "Current assets—Other" and "Deferred charges and other assets—Other" on the balance sheets represents amount of investment in rabbi trusts to fund deferred compensation, pension and other post-retirement benefits for certain management personnel and directors. The funds in the rabbi trusts can only be used to pay for plan participant benefits and other plan expenses such as investment fees or trustee fees. The funds are invested in money market funds at end of December 31, 2018 and September 30, 2018. We did not have any restricted cash at end of September 30, 2017 and 2016. Refer to Note 9- Pension and Other Post-Retirement Benefit Plans for further discussion of rabbi trusts.

Merger with AltaGas Ltd.

Merger with AltaGas Ltd.	3 Months Ended
	Dec. 31, 2018
Merger with AltaGas Ltd. [Abstract]
Merger with Altagas Ltd.	MERGER WITH ALTAGAS LTD. On January 25, 2017 , WGL entered into the Merger Agreement to combine with AltaGas. On July 6, 2018 , the Merger was consummated with WGL becoming an indirect wholly owned subsidiary of AltaGas. In connection with the Merger, WGL established Wrangler SPE LLC, the SPE for the purposes of owning the common stock of Washington Gas in a special purpose bankruptcy remote entity. The SPE is a wholly owned subsidiary of WGL. Following the consummation of the Merger, all of Washington Gas’ outstanding shares of common stock are now owned by the SPE. The Merger had no effect on the Washington Gas preferred stock, which continues to be outstanding. Merger Related Costs The following table summarizes pre-tax merger commitments, legal expense, acceleration of stock-based compensation, and other merger related costs (collectively referred to as merger related costs) that we recorded in connection with the Merger. For the three months ended December 31, 2018, Washington Gas recorded merger related costs of $3.3 million in “Operation and maintenance” on Washington Gas' Statements of Income. For the fiscal year ended September 30, 2018, Washington Gas recorded merger related costs of $ 13.5 million in "Other income (expense)—net" and $ 186.7 million in “Operation and maintenance” on Washington Gas' Statements of Income. MERGER RELATED COSTS (in millions) Three months ended December 31, 2018 Fiscal year ended September 30, 2018 Merger commitments (a) $ 0.4 $ 139.6 Property plant & equipment impairment (b) — 38.0 Key employee retention payments — 10.5 Acceleration of stock-based compensation (c) — 5.4 Severance costs (d) 2.9 6.7 Total $ 3.3 $ 200.2 (a) See the Merger Commitments table below for details of merger related commitments. (b) Net property, plant and equipment impairment recorded in connection with an agreement not to seek recovery of certain costs incurred under the Formal Case 1027 mechanical coupling program. (c) See Note 10-Stock-Based Compensation for further discussion of the acceleration of incentive compensation. (d) Severance costs are related to the retirement of senior executives following the merger. Merger Commitments Approval of the Merger across all jurisdictions was conditioned upon AltaGas and WGL agreeing to certain financial commitments including: customer bill credits, funding for low-income weatherization and energy efficiency initiatives, public safety programs, energy educational programs, gas expansion fund contributions, workplace development initiatives, charitable contributions, and other required commitments. The commitments have been, and will be, funded by AltaGas within various timeframes from 30 days to 10 years after the merger close. In addition, the commitments related to Maryland are subject to a Most Favored Nation (MFN) provision that may change the amount or nature of the commitments. The following table lists total commitments, the amounts paid, and future expected payments as of December 31, 2018. MERGER COMMITMENTS Commitment (Amount in millions) Total Commitment Amount Amount Paid Expected Future Payments Three months ended December 31, 2018 FY 2018 2019 2020 2021 2022 2023 2024-2027 Customer bill credits $ 56.8 $ — $ 56.8 $ — $ — $ — $ — $ — $ — Gas expansion fund contributions 34.2 30.3 — 3.9 — Energy customer or education programs 22.8 — 22.8 — — — — — — Charitable contributions 13.5 0.8 0.4 2.8 1.5 1.5 1.5 1.5 3.5 Work place development initiatives 7.8 — — 3.8 3.8 0.1 0.1 0.1 — Low-income weatherization and energy efficiency initiatives 4.2 — — 2.1 2.1 — — — — Public safety programs 0.7 — — 0.7 — — — — — Total merger commitments $ 140.0 $ 31.1 $ 80.0 $ 13.3 $ 7.4 $ 1.6 $ 1.6 $ 1.6 $ 3.5 The following additional commitments by Washington Gas will have an impact on our consolidated financial statements when the transactions are incurred in the future: 1) Hiring of three damage prevention trainers and community outreach in each jurisdiction for a total of $ 2.4 million over 5 years; 2) Investment of up to $ 70.0 million over a 10-year period to further extend natural gas service to areas within Washington Gas' service territory, which will be incorporated into Washington Gas's ongoing capital plan; 3) Spending $ 8.0 million on leak mitigation and reducing leak backlogs within 3 years after the Merger close; and 4) Development of 15MW of either electric grid energy storage or Tier 1 renewable resources within 5 years. In addition, there are a number of operational commitments that will have an impact on the ongoing business of Washington Gas, including reductions of leak backlogs, conducting a root cause analysis related to customer service, increasing supplier diversity, achieving synergy savings benefits, developing protocols for moving meters from inside to outside customers’ premises, as well as reporting and tracking related to all the commitments. Other Merger Related Items Pursuant to the Merger agreement, Washington Gas contributed $ 66.7 million , which was funded by AltaGas, to rabbi trusts formed to fully satisfy certain outstanding employee benefit obligations immediately prior to the Merger close. See Note 9 — Pension and Other Post-Retirement Benefit Plans for further discussion of the rabbi trusts.

Transition Period Comparative D

Transition Period Comparative Data	3 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Transition Period Comparative Data	NOTE 19. TRANSITION PERIOD COMPARATIVE DATA The following table presents certain financial information for the three months ended December 31, 2018 and 2017. Three Months Ended December 31, $ In thousands 2018 2017 (Unaudited) OPERATING REVENUES $ 402,101 $ 377,470 OPERATING EXPENSES Utility cost of gas 156,641 124,745 Operation and maintenance 102,728 82,372 Depreciation and amortization 34,948 33,646 General taxes and other assessments 38,552 39,983 Total Operating Expenses 332,869 280,746 OPERATING INCOME 69,232 96,724 Other income (expense) — net 3,494 1,029 Interest expense 15,706 14,973 INCOME BEFORE INCOME TAXES 57,020 82,780 INCOME TAX EXPENSE 7,847 24,854 NET INCOME $ 49,173 $ 57,926 Dividends on preferred stock 330 330 NET INCOME APPLICABLE TO COMMON STOCK $ 48,843 $ 57,596 All adjustments necessary for a fair presentation have been included in the quarterly information provided below. Due to the seasonal nature of our business, we report substantial variations in operations on a quarterly basis. Quarter Ended (In thousands) March 31 June 30 September 30 (a) December 31 2018 Operating revenues $ 532,040 $ 199,512 $ 139,041 $ 402,101 Operating income (loss) $ 148,978 $ (6,649 ) $ (225,462 ) 69,232 Net income (loss) $ 108,084 $ (11,499 ) $ (181,153 ) $ 49,173 Net income (loss) applicable to common stock $ 107,754 $ (11,829 ) $ (181,483 ) $ 48,843 2017 Operating revenues $ 475,021 $ 203,186 $ 154,775 $ 377,470 Operating income (loss) $ 164,876 $ 10,482 $ (13,000 ) $ 96,724 Net income (loss) $ 93,610 $ (1,671 ) $ (15,608 ) $ 57,926 Net income (loss) applicable to common stock $ 93,280 $ (2,001 ) $ (15,938 ) $ 57,596 (a) During the quarter ended September 30, 2018, Washington Gas recorded $ 200.2 million of merger related costs due to the Merger with AltaGas.

Quarterly Financial Data

Quarterly Financial Data	3 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	NOTE 19. TRANSITION PERIOD COMPARATIVE DATA The following table presents certain financial information for the three months ended December 31, 2018 and 2017. Three Months Ended December 31, $ In thousands 2018 2017 (Unaudited) OPERATING REVENUES $ 402,101 $ 377,470 OPERATING EXPENSES Utility cost of gas 156,641 124,745 Operation and maintenance 102,728 82,372 Depreciation and amortization 34,948 33,646 General taxes and other assessments 38,552 39,983 Total Operating Expenses 332,869 280,746 OPERATING INCOME 69,232 96,724 Other income (expense) — net 3,494 1,029 Interest expense 15,706 14,973 INCOME BEFORE INCOME TAXES 57,020 82,780 INCOME TAX EXPENSE 7,847 24,854 NET INCOME $ 49,173 $ 57,926 Dividends on preferred stock 330 330 NET INCOME APPLICABLE TO COMMON STOCK $ 48,843 $ 57,596 All adjustments necessary for a fair presentation have been included in the quarterly information provided below. Due to the seasonal nature of our business, we report substantial variations in operations on a quarterly basis. Quarter Ended (In thousands) March 31 June 30 September 30 (a) December 31 2018 Operating revenues $ 532,040 $ 199,512 $ 139,041 $ 402,101 Operating income (loss) $ 148,978 $ (6,649 ) $ (225,462 ) 69,232 Net income (loss) $ 108,084 $ (11,499 ) $ (181,153 ) $ 49,173 Net income (loss) applicable to common stock $ 107,754 $ (11,829 ) $ (181,483 ) $ 48,843 2017 Operating revenues $ 475,021 $ 203,186 $ 154,775 $ 377,470 Operating income (loss) $ 164,876 $ 10,482 $ (13,000 ) $ 96,724 Net income (loss) $ 93,610 $ (1,671 ) $ (15,608 ) $ 57,926 Net income (loss) applicable to common stock $ 93,280 $ (2,001 ) $ (15,938 ) $ 57,596 (a) During the quarter ended September 30, 2018, Washington Gas recorded $ 200.2 million of merger related costs due to the Merger with AltaGas.

Schedule II

Schedule II	3 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts and Reserves	Schedule II—Valuation and Qualifying Accounts and Reserves Three Months Ended December 31, 2018, and Fiscal Years Ended September 30, 2018, 2017 and 2016 Balance at Additions Charged To Balance at Beginning Costs and Other End of (In thousands) of Period Expenses (a) Accounts (b) Deductions (c) Period Three Months Ended December 31, 2018 Valuation and Qualifying Accounts $ 29,622 $ 5,902 $ 581 $ 6,644 $ 29,461 2018 Valuation and Qualifying Accounts Deducted from Assets in the Balance Sheet: Allowance for Doubtful Accounts $ 23,741 $ 19,946 $ 1,409 $ 15,474 $ 29,622 2017 Valuation and Qualifying Accounts Deducted from Assets in the Balance Sheet: Allowance for Doubtful Accounts $ 20,220 $ 14,320 $ 1,821 $ 12,620 $ 23,741 2016 Valuation and Qualifying Accounts Deducted from Assets in the Balance Sheet: Allowance for Doubtful Accounts $ 19,254 $ 10,946 $ 3,806 $ 13,786 $ 20,220 (a) Represent the amount of bad debt expense recorded to the income statement. (b) Recoveries on receivables previously written off as uncollectible and unclaimed customer deposits, overpayments, etc. non refundable. (c) Includes deductions for accounts charged-off.

Accounting Policies (Policies)

Accounting Policies (Policies)	3 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
General Business Combinations	The Merger with AltaGas was recorded using the acquisition method of accounting. Under SEC regulations, Washington Gas elected to not apply push down accounting to its stand alone financial statements. The acquisition adjustments were recorded by AltaGas. On July 6, 2018 , the Merger was consummated between AltaGas, WGL, and the Merger Sub, with WGL surviving as an indirect wholly owned subsidiary of AltaGas. In connection with the Merger, WGL established the SPE for the purposes of owning the common stock of Washington Gas. The SPE is a wholly owned subsidiary of WGL.
Consolidation	The Financial Statements of Washington Gas has been prepared in conformity with GAAP and under the rules of the Securities and Exchange Commission (SEC). The Merger with AltaGas was recorded using the acquisition method of accounting. Under SEC regulations, Washington Gas elected to not apply push down accounting to its stand alone financial statements. The acquisition adjustments were recorded by AltaGas.
Use of Estimates	In accordance with GAAP, we make certain estimates and assumptions regarding: (i) reported assets and liabilities; (ii) disclosed contingent assets and liabilities at the date of the financial statements and (iii) reported revenues, revenues subject to refund, and expenses during the reporting period. Actual results could differ from those estimates.
Inventory Policy	Prior to September 30, 2017, Washington Gas accounted for storage gas inventories using the first-in, first-out method under which the oldest inventory items were recorded as being sold first. Starting in October 1, 2017, Washington Gas implemented a voluntary change in the application of an accounting principle with respect to accounting for natural gas, propane, and odorant inventories. Washington Gas now applies the average cost methodology under which the cost of units carried in inventory is based on the weighted average cost per unit of inventory. Washington Gas implemented the change in accounting principle on a prospective basis in accordance with ASC Topic 980, which permits regulated entities to implement changes for financial reporting purposes in the same way those changes are implemented for regulatory reporting purposes when the change impacts allowable costs. On October 1, 2017, WGL adopted ASU 2015-11, Inventory (Topic 330) - Simplifying the Measurement of Inventory. This standard modified the previous calculation for valuing inventory. As a result of the new standard, beginning October 1, 2017, our inventory balances are stated at the lower of cost or net realizable value. Prior to October 1, 2017, our inventory balances were stated at the lower of cost or market. Interim period inventory losses attributable to lower of cost or net realizable value adjustments may be reversed if the net realizable value of the inventory is recovered by the end of the same fiscal year. Washington Gas did not record a lower-of-cost or net realizable value adjustment to net income for the three months ended December 31, 2018 and fiscal year ended September 30, 2018 or a lower-of-cost or market adjustment to net income for the fiscal year ended September 30, 2017 and 2016.
Property, Plant and Equipment	Property, plant and equipment (comprised principally of utility plant) are stated at original cost, including labor, materials, taxes and overhead costs incurred during the construction period. The cost of utility plant of Washington Gas includes an allowance for funds used during construction (AFUDC) that is calculated under a formula prescribed by our regulators in Maryland and the District of Columbia. Washington Gas capitalizes AFUDC as a component of construction overhead. Washington Gas charges maintenance and repairs directly to operating expenses. Washington Gas capitalizes betterments and renewal costs and calculates depreciation applicable to its utility gas plant in service primarily using a straight-line method over the estimated remaining life of the plant. In accordance with regulatory requirements, such rates include a component related to asset removal costs for Washington Gas. These asset removal costs are accrued through depreciation expense with a corresponding credit to “Regulatory liabilities—Accrued asset removal costs.” When Washington Gas retires depreciable utility plant and equipment, it charges the associated original costs to “Accumulated depreciation and amortization” and any related removal costs incurred are charged to “Regulatory liabilities—Accrued asset removal costs.” Washington Gas periodically reviews the adequacy of its depreciation rates by considering estimated remaining lives and other factors. For information about Asset Retirement Obligations (ARO’s), refer to the section entitled “Asset Retirement Obligations”.
Impairment of Long-Lived Assets	Management regularly reviews property and equipment and other long-lived assets for possible impairment whenever events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. For our properties and equipment, the indicators of potential impairment may include a deteriorating business or legal climate, a significant adverse change in asset condition, specific regulatory disallowance, advances in technology or plans to dispose of an asset significantly before the end of its useful life, among others. Management performs the recoverability test whenever the indicators show a possible impairment. The amount used to test recoverability is determined based on an estimate of undiscounted cash flows, and measurement of an impairment loss is determined based on the fair value of the assets. The determination of fair value requires management to make assumptions about future cash inflows and outflows over the life of an asset. Any changes to the assumptions used for the future cash flow could result in revisions to the evaluation of the recoverability of the long-lived assets and the recognition of an impairment loss in the Consolidated Financial Statements.
Operating Leases	We have classified the leases of multiple office locations as operating leases. We amortize as rent expense the total of all scheduled lease payments (including lease payment escalations) and tenant allowances on a straight-line basis over the term of the leases. For this purpose, the lease term begins on the date when the lessor commenced constructing the leasehold improvements which allowed us to occupy the respective locations. Leasehold improvement costs are classified as “Property, Plant and Equipment” on the Balance Sheets, and are being amortized to depreciation and amortization expense on a straight-line basis over the non-cancelable period of the leases.
Cash and Cash Equivalents	We consider all investments with original maturities of three months or less to be cash equivalents
Restricted Cash and Cash Equivalents	Restricted cash and cash equivalents represent funds that are restricted to satisfy designated liabilities. Restricted cash and cash equivalents available to satisfy designated current liabilities are classified as current assets. Restricted cash and cash equivalents expected to satisfy non-current liabilities are classified as non-current assets.
Revenue Recognition	Revenues. The Utility recognizes revenue from contracts with customers to depict the transfer of goods or services to customers at an amount it expects to be entitled to in exchange for those goods or services. Generally, goods or services are transferred to our customer when the natural gas is delivered. Washington Gas reads meters and bills customers on a 19 -day monthly cycle basis. The billing cycles for customers do not coincide with the accounting periods used for financial reporting purposes; therefore, Washington Gas accrues unbilled revenues for gas delivered, but not yet billed, at the end of each accounting period. Refer to Note 2 - Revenue from Contracts with Customers for further discussion of the Utility’s revenue from contracts with customers.
Revenue Recognition for Alternative Revenue Programs, Policy	Alternative Revenue Programs. Certain ratemaking mechanisms of Washington Gas qualify as alternative revenue programs in accordance with ASC Topic 980, Regulated Operations, if the program (i) is established by an order from the regulatory commissions and allows for automatic adjustment of future rates, (ii) the additional revenues (above those amounts currently reflected in base rates) that are objectively determinable and probable of recovery, and (iii) allow for the collection of the additional revenues within 24 months following the end of the period in which they were recognized. The Company has determined that its RNA, WNA and CRA billing adjustment mechanisms and accelerated pipe replacement programs are alternative revenue programs. Alternative revenue program revenues represent the initial recognition of revenue related to these programs. When amounts are billed and collected from customers through rates, the amounts are recorded as a recovery of the associated regulatory asset or liability.
Utility cost of gas and revenue taxes	Cost of Gas. Washington Gas’ jurisdictional tariffs contain mechanisms that provide for the recovery of the cost of gas incurred on behalf of firm customers, including related pipeline transportation and storage capacity charges. Under these mechanisms, Washington Gas periodically adjusts its firm customers’ rates to reflect increases and decreases in these costs. Under or over-collections of gas costs in the current cycle are charged or credited to deferred charges or credits on the balance sheet as non-current regulatory assets or liabilities. Amounts deferred at the end of the cycle, August 31 of each year, are fully reconciled and transferred to current assets or liabilities under the balance sheet captions “Gas costs and other regulatory assets” and “Gas costs and other regulatory liabilities.” These balances are recovered or refunded to customers over the subsequent 12 month period. Revenue Taxes. Revenue taxes such as gross receipts taxes, Public Service Commission (PSC) fees, franchise fees and energy taxes are reported gross in operating revenues.
Transportation Gas Imbalance	Interruptible shippers and third-party marketer shippers transport gas to Washington Gas’ distribution system as part of the unbundled services offered. The delivered volumes of gas from third-party shippers into Washington Gas’ distribution system rarely equal the volumes billed to third-party marketer customers, resulting in transportation gas imbalances. These imbalances are usually short-term in duration, and Washington Gas monitors the activity and regularly notifies the shippers when their accounts have an imbalance. In accordance with regulatory treatment, Washington Gas does not record a receivable from or liability to third-party marketers associated with gas volumes related to these transportation imbalances but, rather, reflects the financial impact as a regulatory asset or liability related to its gas cost adjustment mechanism, thereby eliminating any profit or loss that would occur as a result of the imbalance. The regulatory treatment combines the imbalance for all marketers, including our affiliate WGL Energy Services, into a single “net” adjustment to the regulatory asset or liability.
Asset Optimization Program	Washington Gas optimizes the value of its long-term natural gas transportation and storage capacity resources by entering into physical and financial transactions in the form of forwards, futures and option contracts for periods when these resources are not being used to physically serve utility customers. Refer to “Derivative Activities” below for further discussion of the accounting for derivative transactions entered into under this program. Regulatory sharing mechanisms in all three jurisdictions allow the profit from these transactions to be shared between Washington Gas’ customers and shareholder. All unrealized fair value gains and losses, and margins generated from the physical and financial settlement of these asset optimization contracts are recorded in "Utility cost of gas" on the income statement or, in the case of amounts to be shared with rate payers, regulatory assets/liabilities on the balance sheet.
Stock-based compensation	We account for stock-based compensation expense in accordance with ASC Topic 718, Compensation-Stock Compensation, and all outstanding awards as of December 31, 2018 are liability-classified share-based awards. We recognize stock-based compensation expense based on their fair value at the end of each reporting period. In addition, certain awards are accounted for under ASC Topic 710, Compensation - General, because they do not meet the definition of a stock-based award under ASC Topic 718. Compensation expense is recognized based on the probable outcome of the award at the end of each reporting period. We estimate forfeitures over the requisite service period when recognizing compensation expense; these estimates are periodically adjusted to the extent to which actual forfeitures differ from such estimates.
Asset Retirement Obligations	Washington Gas accounts for its AROs in accordance with ASC Subtopic 410-20, Asset Retirement and Environmental Obligations—Asset Retirement Obligations. Our AROs include the costs to cut, purge and cap Washington Gas' distribution and transmission system and plug storage wells upon their retirement. These standards require recording the estimated retirement cost over the life of the related asset by depreciating the present value of the retirement obligation, measured at the time of the asset’s acquisition, and accreting the liability until it is settled. There are timing differences between the ARO-related accretion and depreciation amounts being recorded pursuant to GAAP and the recognition of depreciation expense for legal asset removal costs that we are currently recovering in rates. These timing differences are recorded as a reduction to “Regulatory liabilities—Accrued asset removal costs” in accordance with ASC Topic 980. We do not have any assets that are legally restricted related to the settlement of asset retirement obligations.
Accounting Standards Adopted in the Current Fiscal Year	ASU 2014-09, Revenue from Contracts with Customers (Topic 606), including subsequent ASUs clarifying the guidance. ASU 2014-09 establishes a comprehensive revenue recognition model clarifying the method used to determine the timing and requirements for revenue recognition from contracts with customers. The disclosure requirements under the new standard will enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. October 1, 2018 Washington Gas adopted the new guidance using the modified retrospective approach, which does not require prior year results to be restated. Adoption of this standard did not have a material change in the timing or pattern of revenue recognition and a cumulative-effect adjustment was not recorded at October 1, 2018. The significant impact of adopting this standard is the additional disclosures around the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. For the new disclosures, see the Revenue and Cost Recognition discussion above and Note 2 - Revenue from Contracts with Customers . ASU 2016-01, Financial Instruments (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities including subsequent ASUs clarifying the guidance. This guidance applies to the recognition and measurement of financial assets and liabilities. The standard requires equity investments, except those accounted for under the equity method of accounting or consolidated, to be measured at fair value with changes in the fair value recognized in net income. The standard also amends presentation requirements related to certain changes in the fair value of a liability and eliminates certain disclosure requirements of significant assumptions for financial instruments measured at amortized cost on the balance sheet. October 1, 2018 The adoption of this standard and related amendments did not have a material impact on our consolidated financial statements or on our disclosures. 2016-16, Income Taxes (Topic 740): Intra-entity Transfers of Assets Other Than Inventory This standard revised the accounting for income taxes by requiring an entity to recognize the current and deferred income tax consequences of an intra-entity asset transfer (other than inventory) when the transfer occurs. The standard should be applied on modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. October 1, 2018 The adoption of this standard and related amendments did not have a material effect on the financial statements. ASU No. 2017-01, (Topic 805): Business Combinations - Clarifying the Definition of a Business This standard changed the definition of a business to assist entities with the evaluation of whether a transaction should be accounted for as an acquisition (or disposal) of assets or a business. The standard should be applied on a prospective basis to transactions that occur on or after the effective date. October 1, 2018 Washington Gas will apply the amendments in this standard on a prospective basis and did not have an impact on the financial statements. ASU 2017-05, Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets The amendments in this ASU clarified the scope of ASC 610-20, as well as, the accounting for partial sales of nonfinancial assets. The standard can be applied either on a retrospective basis or on a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. October 1, 2018 The adoption of this standard did not have an impact on the financial statements. ASU 2017-07, Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost This standard requires entities to report the service cost component in the same financial statement line item as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are to be presented separately from service cost and outside of operating income. In addition, only the service cost component of net benefit cost is eligible for capitalization. Changes to the presentation of service costs and other components of net benefit cost should be applied retrospectively. Changes in capitalization practices should be implemented prospectively. October 1, 2018 We have concluded our evaluation of the interaction of this standard with the various regulatory provisions concerning pensions and post-retirement benefit costs. For the fiscal years ended September 30, 2018, 2017 and 2016, we recorded a reclassification of $11.3 million, $3.9 million and $3.6 million, respectively, of net periodic benefit income from operation and maintenance expenses to other income in the Statement of Income. The change in capitalization of retirement benefits have been implemented on a prospective basis and did not have a material impact on the financial statements. ASU 2017-09, Compensation-Stock Compensation (Topic 718): Scope of Modification Accounting This standard provided guidance on the types of changes to the terms or conditions of a shared-based payment arrangement should apply modification accounting. The amendments should be applied on a prospective basis to awards modified on or after the effective date. October 1, 2018 The guidance in this standard was applied on a prospective basis and did not have an impact on the financial statements. ASU 2018-08, Not-for-Profit Entities (Topic 958)-Clarifying the Scope and the Accounting Guidance for Contributions Received and Contributions Made This standard provides clarification to assist entities in evaluating whether transactions should be accounted for as a contribution (nonreciprocal) or as an exchange (reciprocal) subject to other accounting guidance. The amendments should be applied on a modified prospective basis, however; retrospective application is permitted. October 1, 2018 The guidance in this standard did not have an impact on the financial statements.
Other New Accounting Pronouncements	ASU 2016-02, Leases (Topic 842), ASU 2018-01, Land Easement Practical Expedient for Transition to Topic 842, and ASU 2018-11, Targeted Improvements, including other subsequent ASUs clarifying the guidance ASU 2016-02 requires recognition of a right-to-use asset and lease liability by lessees on the statement of financial position and disclosure of key information about leasing arrangements. Lessor accounting remains substantially unchanged but the standard modifies what qualifies as a sales-type and direct financing lease and eliminated real-estate specific provisions. January 1, 2019 Washington Gas is in the final stages of evaluating the impact of adopting ASC Topic 842. Washington Gas will utilize the transition practical expedients which allow entities to not have to reassess whether an arrangement contains a lease and the lease classification under the provisions of ASC Topic 842, land easements, and not separating out the lease and non-lease components for certain classes of assets. Washington Gas has also elected to present prior comparative information under ASC 840. For its lessee leases with terms longer than 12 months, Washington Gas will be recording an increase to long-term assets (net of any lease incentives and prepaid or deferred rent balances) and an increase to noncurrent liabilities net of the current portion to be recorded in current liabilities. The total liabilities are currently estimated to be approximately 1 percent of total assets but may change as Washington Gas finalizes its evaluation of the impact of the standard. ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted improvements to Accounting for Hedging Activities The new standard amends the hedge accounting and recognition requirements by expanding an entity's ability to hedge non-financial and financial risk components and reduce the complexity in fair value hedges of interest rate risk. Additionally, this standard eliminates the requirement to separately measure and disclose the ineffective portion of the hedge with the entire change in the fair value of a hedging instrument to be presented in the same income statement line as the hedged item. Early adoption is permitted. January 1, 2019 The guidance would be applicable to Washington Gas and only have an impact on new transactions that are entered into and where hedge accounting is elected. ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, including other subsequent ASUs clarifying the guidance. For credit losses on financial instruments, this standard changes the current incurred loss impairment methodology to an expected loss methodology and requires consideration of a broader range of reasonable and supportable information to determine credit loss estimates. Early adoption is permitted. January 1, 2020 We are in the process of evaluating the impact the adoption of this standard will have on our financial statements. Early adoption is permitted. ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement This update modifies the disclosure requirements on fair value measurements. Early adoption is permitted. January 1, 2020 It is not expected that the adoption of this standard will have a material effect on our financial statements. ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (a consensus of the FASB Emerging Issues Task Force) The update aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements to capitalize implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). Capitalized implementation costs should be presented in the statement of financial position as a prepaid expense and amortized over the term of the hosting arrangement, presented in the statements of income in the same line items as prepayment of fees associated with the hosting arrangement. The updates in this standard may be applied on a prospective or retrospective basis. Early adoption is permitted. January 1, 2020 The adoption of this ASU is not expected to have a material effect on our financial statements. ASU 2018-17, Consolidation (Topic 810): Targeted Improvements to Related Party Guidance for Variable Interest Entities This standard provides a private-company scope exception to the VIE guidance for certain entities under common control and clarify that indirect interest held through related parties under common control will be considered on a proportional basis when determining whether fees paid to decision makers and service providers are variable interests. Early adoption is permitted. January 1, 2020 We are in the process of evaluating this new accounting standard but it is expected that the adoption of this standard will not have a material effect on our financial statements. ASU 2018-14, Compensation—Retirement Benefits—Defined Benefit Plans—General (Subtopic 715-20): Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans This standard modifies the disclosure requirements related to defined benefit pension and other postretirement plans. Early adoption is permitted. December 31, 2020 We do not anticipate that adoption of this standard will have a material effect on our financial statements.

Revenue from Contracts With C_2

Revenue from Contracts With Customers - (Policies)	3 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Washington Gas sells natural gas and distribution services to residential, commercial, industrial and governmental customers through regulated tariff rates approve by regulatory commissions in the jurisdictions where Washington Gas operates. Customers are billed monthly based on regular meter readings. Customer billings are based on two main components: (i) a fixed service fee and (ii) a variable fee based on usage. Revenue is recognized over time as the natural gas is delivered or as the service has been performed. As meter readings are performed on a cycle basis, Washington Gas recognizes accrued revenue for any services rendered to its customers but not billed at month-end. The tariff sales are generally considered daily or “at-will” contracts as customers may cancel their service at any time, and revenue generally represents the amount the Utility is entitled to invoice. There are certain contracts that have terms of one year or longer. For these contracts, revenue is recognized based on the amount the Utility is entitled to bill the customer. Customers have the choice to purchase natural gas from competitive service providers. The Utility charges the competitive service providers balancing fees to manage the natural gas transportation imbalances. Where regulations require, the Utility issues customers a consolidated bill to include the natural gas supplied by the competitive service providers and distribution of natural gas. Washington Gas recognizes revenue only for distribution services that the Utility has provided to the customer, and the balancing fees for the services provided to the competitive service provider.

Regulated Operations (Policies)

Regulated Operations (Policies)	3 Months Ended
	Dec. 31, 2018
Regulated Operations [Abstract]
Regulated Operations Policy	Washington Gas accounts for its regulated operations in accordance with ASC Topic 980. This standard includes accounting principles for companies whose rates are determined by independent third-party regulators. When setting rates, regulators may require us to record expense in different periods than may be appropriate for unregulated enterprises. When this occurs, Washington Gas defers the associated costs as assets (regulatory assets) on its balance sheet and records them as expenses on its income statement as it collects the revenues designed to recover these costs through customers’ rates. Further, regulators can also impose liabilities upon a company for gains previously realized or for amounts previously collected from customers for expenses expected to be incurred in the future (regulatory liabilities).

Short-Term Debt (Policies)

Short-Term Debt (Policies)	3 Months Ended
	Dec. 31, 2018
Short-term Debt [Abstract]
Short Term Debt Policy	Washington Gas satisfies the short-term financing requirements through the sale of commercial paper, financing arrangements with third-party lenders, or through bank borrowings. Due to the seasonal nature of our operations, short-term financing requirements can vary significantly during the year. Revolving credit agreements are maintained to support outstanding commercial paper and to permit short-term borrowing flexibility. The policy of Washington Gas is to maintain bank credit facilities in amounts equal to or greater than the expected maximum commercial paper position. Washington Gas issues long-term debt in the form of MTNs, unsecured long-term notes and private placement notes with individual terms regarding interest rates, maturities and call or put options. These notes can have maturity dates of one or more years from the date of issuance.

Long-Term Debt Long-Term Debt (

Long-Term Debt Long-Term Debt (Policies)	3 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Long Term Debt Policy	Washington Gas satisfies the short-term financing requirements through the sale of commercial paper, financing arrangements with third-party lenders, or through bank borrowings. Due to the seasonal nature of our operations, short-term financing requirements can vary significantly during the year. Revolving credit agreements are maintained to support outstanding commercial paper and to permit short-term borrowing flexibility. The policy of Washington Gas is to maintain bank credit facilities in amounts equal to or greater than the expected maximum commercial paper position. Washington Gas issues long-term debt in the form of MTNs, unsecured long-term notes and private placement notes with individual terms regarding interest rates, maturities and call or put options. These notes can have maturity dates of one or more years from the date of issuance.

Income Taxes Income Taxes (Poli

Income Taxes Income Taxes (Policies)	3 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Income Taxes Policy	Effective with the Merger and beginning July 7, 2018, our tax year end changed to December 31 and Washington Gas will be included with AltaGas’ wholly owned US subsidiaries’ consolidated income tax return with AltaGas Services (U.S.), (ASUS) being the parent company of the consolidated group. Accordingly, Washington Gas will file a final return as part of the WGL 's consolidated income tax return for the short tax year from October 1, 2017 to July 6, 2018. WGL and its wholly owned subsidiaries will be included in the AltaGas' consolidated income tax returns beginning with the period from July 7, 2018 to December 31, 2018. We have established a new tax sharing policy with ASUS. The tax sharing policy provides allocation of consolidated tax liabilities and benefits based on amounts participants would incur as standalone corporations. Income taxes recorded for the period October 1, 2017 through July 6, 2018 are based on amounts we would incur as standalone corporations. State income tax returns are filed on a separate company basis in most states and on a unitary basis as required, where we or the consolidated ASUS group have operations and/or a requirement to file. Through July 6th and prior to the Merger with AltaGas, WGL and its wholly owned subsidiaries filed a consolidated federal income tax return and various state income tax returns where they had a business presence. We are no longer subject to income tax examinations by the Internal Revenue Service (IRS) for years ended September 30, 2013 and prior. Substantially all state income tax years in major jurisdictions are closed for years ended prior to September 30, 2015. Through July 6, 2018, WGL and each of its subsidiaries participated in a tax sharing agreement that establishes the method for allocating tax benefits from losses that are utilized on the consolidated income tax return. The consolidated tax is apportioned among the subsidiaries on the separate return method and losses are allocated to the subsidiaries that have taxable income pro-rata basis.

Environmental Matters (Policies

Environmental Matters (Policies)	3 Months Ended
	Dec. 31, 2018
Environmental Remediation Obligations [Abstract]
Environmental Matters Policy	We are subject to federal, state and local laws and regulations related to environmental matters. These laws and regulations may require expenditures over a long-time frame to control environmental effects. Almost all of the environmental liabilities we have recorded are for costs expected to be incurred to remediate sites where we or a predecessor affiliate operated MGPs. Estimates of liabilities for environmental response costs are difficult to determine with precision because of the various factors that can affect their ultimate level. These factors include, but are not limited to, the following: • the complexity of the site; • changes in environmental laws and regulations at the federal, state and local levels; • the number of regulatory agencies or other parties involved; • new technology that renders previous technology obsolete or experience with existing technology that proves ineffective; • the level of remediation required; and • variations between the estimated and actual period of time that must be dedicated to respond to an environmentally-contaminated site.

Derivative and Weather Relate_2

Derivative and Weather Related Instruments (Policies)	3 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives, Policy	Washington Gas enters into contracts that qualify as derivative instruments and are accounted for under ASC Topic 815. These derivative instruments are recorded at fair value on our balance sheets and Washington Gas does not currently designate any derivatives as hedges under ASC Topic 815. Washington Gas’ derivative instruments relate to: (i) Washington Gas’ asset optimization program; (ii) managing price risk associated with the purchase of gas to serve utility customers and (iii) managing interest rate risk. Asset Optimization. Washington Gas optimizes the value of its long-term natural gas transportation and storage capacity resources during periods when these resources are not being used to physically serve utility customers. Specifically, Washington Gas utilizes its transportation capacity assets to benefit from favorable natural gas prices between different geographic locations and utilizes its storage capacity assets to benefit from favorable natural gas prices between different time periods. As part of this asset optimization program, Washington Gas enters into physical and financial derivative transactions in the form of forward, futures and option contracts with the primary objective of securing operating margins that Washington Gas will ultimately realize. The derivative transactions entered into under this program are subject to mark-to-market accounting treatment under ASC Topic 820. Regulatory sharing mechanisms provide for the annual realized profit from these transactions to be shared between Washington Gas' shareholders and customers; therefore, changes in fair value are recorded through earnings, or as regulatory assets or liabilities to the extent that it is probable that realized gains and losses associated with these derivative transactions will be included in the rates charged to customers when they are realized. Unrealized gains and losses recorded to earnings may cause significant period-to-period volatility; this volatility does not change the operating margins that Washington Gas expects to ultimately realize from these transactions through the use of its storage and transportation capacity resources.
Risk, Policy	Managing Price Risk. To manage price risk associated with acquiring natural gas supply for utility customers, Washington Gas enters into physical and financial derivative transactions in the form of forward, option and other contracts, as authorized by its regulators. Any gains and losses associated with these derivatives are recorded as regulatory liabilities or assets, respectively, to reflect the rate treatment for these economic hedging activities. Managing Interest-Rate Risk. Washington Gas may utilize derivative instruments that are designed to minimize the risk of interest-rate volatility associated with planned issuances of debt securities. Any gains and losses associated with these types of derivatives are recorded as regulatory liabilities or assets, respectively, and amortized in accordance with regulatory requirements, typically over the life of the related debt.
Collateral, Policy	Washington Gas utilizes standardized master netting agreements, which facilitate the netting of cash flows into a single net exposure for a given counterparty. As part of these master netting agreements, cash, letters of credit and parent company guarantees may be required to be posted or obtained from counterparties in order to mitigate credit risk related to both derivatives and non-derivative positions. Under Washington Gas' offsetting policy, collateral balances are offset against the related counterparties’ derivative positions to the extent the application would not result in the over-collateralization of those derivative positions on the balance sheet. Any collateral posted that is not offset against derivative assets and liabilities is included in “Other prepayments” in the accompanying balance sheets. Collateral received and not offset against derivative assets and liabilities is included in “Customer deposits and advance payments” in the accompanying balance sheets. Concentration of Credit Risk We are exposed to credit risk from derivative instruments with wholesale counterparties, which is represented by the fair value of these instruments at the reporting date. We actively monitor and work to minimize counterparty concentration risk through various practices. We are exposed to credit risk from derivative instruments with wholesale counterparties, which is represented by the fair value of these instruments at the reporting date. We actively monitor and work to minimize counterparty concentration risk through various practices.

Fair Value Measurements Fair Va

Fair Value Measurements Fair Value (Policies)	3 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Fair Value Measurement Policy	A financial instrument’s classification within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement requires judgment and may affect the valuation of fair value assets and liabilities and their placement within the fair value hierarchy. Recurring Basis We measure the fair value of our financial assets and liabilities using a combination of the income and market approaches in accordance with ASC Topic 820. These financial assets and liabilities primarily consist of derivatives recorded on our balance sheet under ASC Topic 815 and short-term investments, commercial paper and long-term debt outstanding required to be disclosed at fair value. Under ASC Topic 820, fair value is defined as the exit price, representing the amount that would be received in the sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. To value our financial instruments, we use market data or assumptions that market participants would use, including assumptions about credit risk (both our own credit risk and the counterparty’s credit risk) and the risks inherent in the inputs to valuation. We enter into derivative contracts in the futures and over-the-counter (OTC) wholesale and retail markets. These markets are the principal markets for the respective wholesale and retail contracts. Our relevant market participants are our existing counterparties and others who have participated in energy transactions at our delivery points. These participants have access to the same market data as Washington Gas. Valuations are generally based on pricing service data or indicative broker quotes depending on the market location. We measure the net credit exposure at the counterparty level where the right to set-off exists. The net exposure is determined using the mark-to-market exposure adjusted for collateral, letters of credit and parent guarantees. We use published default rates from Standard & Poor’s Ratings Services and Moody’s Investors Service as inputs for determining credit adjustments. Our Risk Analysis and Mitigation (RA&M) Group determines the valuation policies and procedures. The RA&M Group reports to Washington Gas' Chief Financial Officer. In accordance with Washington Gas valuation policy, we may utilize a variety of valuation methodologies to determine the fair value of Level 3 derivative contracts, including internally developed valuation inputs and pricing models. The prices used in our valuations are corroborated using multiple pricing sources, and we periodically conduct assessments to determine whether each valuation model is appropriate for its intended purpose. The RA&M Group also evaluates changes in fair value measurements on a daily basis.
Fair Value Transfer, Policy	Transfers between different levels of the fair value hierarchy may occur based on fluctuations in the valuation inputs and on the level of observable inputs used to value the instruments from period to period. It is our policy to show both transfers into and out of the different levels of the fair value hierarchy at the fair value as of the beginning of the period. Transfers out of Level 3 during the three months ended December 31, 2018 , and fiscal years ended September 30, 2018 and September 30, 2017 were due to valuations that experienced an increase in observable market inputs. Transfers into Level 3 during the three months ended December 31, 2018 , and fiscal years ended September 30, 2018 and September 30, 2017 were due to an increase in unobservable market inputs, primarily pricing points.
Fair Value of Financial Instruments, Policy	Our money market funds are Level 1 valuations and their carrying amount approximates fair value. The maturity of our commercial paper outstanding at both December 31, 2018 , September 30, 2018 and September 30, 2017 is under 30 days. Due to the short term nature of these notes, the carrying cost of our commercial paper approximates fair value using Level 2 inputs. Due to the nature of our project financing arrangements, the carrying cost approximates fair value using Level 2 inputs. Due to the short term nature of current maturities of long-term debt, the carrying cost approximates fair value using level 2 inputs, Washington Gas’ long-term debt is not actively traded. The fair value of long-term debt was estimated based on valuation techniques when observable market data is not available. Our long-term debt fair value measurement is classified as Level 3.

Accounting Policies (Tables)

Accounting Policies (Tables)	3 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Property, Plant, and Equipment at Original Cost	The following table represents the components of Washington Gas' Property, Plant and Equipment at original cost. Property, Plant and Equipment at Original Cost ($ In millions) December 31, September 30, 2018 2018 2017 Distribution, transmission and storage $ 4,888.4 85.7 % $ 4,766.5 84.9 % $ 4,502.6 84.8 % General, miscellaneous and intangibles 542.9 9.5 % 536.4 9.6 % 545.6 10.2 % Construction work in progress (CWIP) 271.6 4.8 % 310.2 5.5 % 262.1 5.0 % Total 5,702.9 100.0 % 5,613.1 100.0 % 5,310.3 100.0 %
Changes in Asset Retirement Obligations	Changes in Asset Retirement Obligations (In millions) December 31, September 30, 2018 2018 2017 Asset retirement obligations at beginning of year $ 305.5 $ 298.9 $ 206.6 Liabilities incurred in the period — 1.4 2.0 Revaluation of asset retirement obligation — — 89.5 Liabilities settled in the period — (7.3 ) (7.2 ) Accretion expense 2.6 12.5 8.0 Asset retirement obligations at the end of the year (a) $ 308.1 $ 305.5 $ 298.9 (a)Includes short-term asset retirement obligations of $7.3 million , $7.3 million and $7.1 million for three months ended December 31, 2018, and fiscal years ended September 30, 2018 and September 30, 2017 , respectively.
Accounting standards adopted in the current fiscal year	The following tables represent accounting standards adopted by Washington Gas during the three-month transition period ended December 31, 2018, and other newly issued accounting standards that will be adopted by Washington Gas in the future. ACCOUNTING STANDARDS ADOPTED IN THREE MONTHS TRANSITION PEPRIOD Standard Description Date of adoption Effect on the financial statements or other significant matters ASU 2014-09, Revenue from Contracts with Customers (Topic 606), including subsequent ASUs clarifying the guidance. ASU 2014-09 establishes a comprehensive revenue recognition model clarifying the method used to determine the timing and requirements for revenue recognition from contracts with customers. The disclosure requirements under the new standard will enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. October 1, 2018 Washington Gas adopted the new guidance using the modified retrospective approach, which does not require prior year results to be restated. Adoption of this standard did not have a material change in the timing or pattern of revenue recognition and a cumulative-effect adjustment was not recorded at October 1, 2018. The significant impact of adopting this standard is the additional disclosures around the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. For the new disclosures, see the Revenue and Cost Recognition discussion above and Note 2 - Revenue from Contracts with Customers . ASU 2016-01, Financial Instruments (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities including subsequent ASUs clarifying the guidance. This guidance applies to the recognition and measurement of financial assets and liabilities. The standard requires equity investments, except those accounted for under the equity method of accounting or consolidated, to be measured at fair value with changes in the fair value recognized in net income. The standard also amends presentation requirements related to certain changes in the fair value of a liability and eliminates certain disclosure requirements of significant assumptions for financial instruments measured at amortized cost on the balance sheet. October 1, 2018 The adoption of this standard and related amendments did not have a material impact on our consolidated financial statements or on our disclosures. 2016-16, Income Taxes (Topic 740): Intra-entity Transfers of Assets Other Than Inventory This standard revised the accounting for income taxes by requiring an entity to recognize the current and deferred income tax consequences of an intra-entity asset transfer (other than inventory) when the transfer occurs. The standard should be applied on modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. October 1, 2018 The adoption of this standard and related amendments did not have a material effect on the financial statements. ASU No. 2017-01, (Topic 805): Business Combinations - Clarifying the Definition of a Business This standard changed the definition of a business to assist entities with the evaluation of whether a transaction should be accounted for as an acquisition (or disposal) of assets or a business. The standard should be applied on a prospective basis to transactions that occur on or after the effective date. October 1, 2018 Washington Gas will apply the amendments in this standard on a prospective basis and did not have an impact on the financial statements. ASU 2017-05, Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets The amendments in this ASU clarified the scope of ASC 610-20, as well as, the accounting for partial sales of nonfinancial assets. The standard can be applied either on a retrospective basis or on a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. October 1, 2018 The adoption of this standard did not have an impact on the financial statements. ASU 2017-07, Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost This standard requires entities to report the service cost component in the same financial statement line item as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are to be presented separately from service cost and outside of operating income. In addition, only the service cost component of net benefit cost is eligible for capitalization. Changes to the presentation of service costs and other components of net benefit cost should be applied retrospectively. Changes in capitalization practices should be implemented prospectively. October 1, 2018 We have concluded our evaluation of the interaction of this standard with the various regulatory provisions concerning pensions and post-retirement benefit costs. For the fiscal years ended September 30, 2018, 2017 and 2016, we recorded a reclassification of $11.3 million, $3.9 million and $3.6 million, respectively, of net periodic benefit income from operation and maintenance expenses to other income in the Statement of Income. The change in capitalization of retirement benefits have been implemented on a prospective basis and did not have a material impact on the financial statements. ASU 2017-09, Compensation-Stock Compensation (Topic 718): Scope of Modification Accounting This standard provided guidance on the types of changes to the terms or conditions of a shared-based payment arrangement should apply modification accounting. The amendments should be applied on a prospective basis to awards modified on or after the effective date. October 1, 2018 The guidance in this standard was applied on a prospective basis and did not have an impact on the financial statements. ASU 2018-08, Not-for-Profit Entities (Topic 958)-Clarifying the Scope and the Accounting Guidance for Contributions Received and Contributions Made This standard provides clarification to assist entities in evaluating whether transactions should be accounted for as a contribution (nonreciprocal) or as an exchange (reciprocal) subject to other accounting guidance. The amendments should be applied on a modified prospective basis, however; retrospective application is permitted. October 1, 2018 The guidance in this standard did not have an impact on the financial statements.
Other newly issued accounting standards	OTHER NEWLY ISSUED ACCOUNTING STANDARDS Standard Description Required date of adoption Effect on the financial statements or other significant matters ASU 2016-02, Leases (Topic 842), ASU 2018-01, Land Easement Practical Expedient for Transition to Topic 842, and ASU 2018-11, Targeted Improvements, including other subsequent ASUs clarifying the guidance ASU 2016-02 requires recognition of a right-to-use asset and lease liability by lessees on the statement of financial position and disclosure of key information about leasing arrangements. Lessor accounting remains substantially unchanged but the standard modifies what qualifies as a sales-type and direct financing lease and eliminated real-estate specific provisions. January 1, 2019 Washington Gas is in the final stages of evaluating the impact of adopting ASC Topic 842. Washington Gas will utilize the transition practical expedients which allow entities to not have to reassess whether an arrangement contains a lease and the lease classification under the provisions of ASC Topic 842, land easements, and not separating out the lease and non-lease components for certain classes of assets. Washington Gas has also elected to present prior comparative information under ASC 840. For its lessee leases with terms longer than 12 months, Washington Gas will be recording an increase to long-term assets (net of any lease incentives and prepaid or deferred rent balances) and an increase to noncurrent liabilities net of the current portion to be recorded in current liabilities. The total liabilities are currently estimated to be approximately 1 percent of total assets but may change as Washington Gas finalizes its evaluation of the impact of the standard. ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted improvements to Accounting for Hedging Activities The new standard amends the hedge accounting and recognition requirements by expanding an entity's ability to hedge non-financial and financial risk components and reduce the complexity in fair value hedges of interest rate risk. Additionally, this standard eliminates the requirement to separately measure and disclose the ineffective portion of the hedge with the entire change in the fair value of a hedging instrument to be presented in the same income statement line as the hedged item. Early adoption is permitted. January 1, 2019 The guidance would be applicable to Washington Gas and only have an impact on new transactions that are entered into and where hedge accounting is elected. ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, including other subsequent ASUs clarifying the guidance. For credit losses on financial instruments, this standard changes the current incurred loss impairment methodology to an expected loss methodology and requires consideration of a broader range of reasonable and supportable information to determine credit loss estimates. Early adoption is permitted. January 1, 2020 We are in the process of evaluating the impact the adoption of this standard will have on our financial statements. Early adoption is permitted. ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement This update modifies the disclosure requirements on fair value measurements. Early adoption is permitted. January 1, 2020 It is not expected that the adoption of this standard will have a material effect on our financial statements. ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (a consensus of the FASB Emerging Issues Task Force) The update aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements to capitalize implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). Capitalized implementation costs should be presented in the statement of financial position as a prepaid expense and amortized over the term of the hosting arrangement, presented in the statements of income in the same line items as prepayment of fees associated with the hosting arrangement. The updates in this standard may be applied on a prospective or retrospective basis. Early adoption is permitted. January 1, 2020 The adoption of this ASU is not expected to have a material effect on our financial statements. ASU 2018-17, Consolidation (Topic 810): Targeted Improvements to Related Party Guidance for Variable Interest Entities This standard provides a private-company scope exception to the VIE guidance for certain entities under common control and clarify that indirect interest held through related parties under common control will be considered on a proportional basis when determining whether fees paid to decision makers and service providers are variable interests. Early adoption is permitted. January 1, 2020 We are in the process of evaluating this new accounting standard but it is expected that the adoption of this standard will not have a material effect on our financial statements. ASU 2018-14, Compensation—Retirement Benefits—Defined Benefit Plans—General (Subtopic 715-20): Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans This standard modifies the disclosure requirements related to defined benefit pension and other postretirement plans. Early adoption is permitted. December 31, 2020 We do not anticipate that adoption of this standard will have a material effect on our financial statements.

Revenue from Contracts With C_3

Revenue from Contracts With Customers - (Tables)	3 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following table disaggregates revenue for the period ended December 31, 2018: Disaggregated Revenue by Type of Service (In millions) Three Months Ended December 31, 2018 Revenue from contracts with customers Gas and transportation sales Gas sold and delivered $ 303.2 Gas delivered for others 74.3 Other 12.5 Other revenues 1.5 Total revenue from contracts with customers $ 391.5 Other sources of revenue Revenue from alternative revenue programs (a) $ 9.1 Leasing revenue (b) 0.2 Other 1.3 Total revenue from other sources 10.6 Total Operating Revenue $ 402.1 (a) The company has determined that the Utility’s RNA, WNA and CRA billing adjustment mechanisms and accelerated pipe replacement programs are alternative revenue programs and accounted for under ASC Topic 980. (b) Revenue generated from Washington Gas lessor operating leases accounted for under ASC Topic 840, Leases.

Regulated Operations (Tables)

Regulated Operations (Tables)	3 Months Ended
	Dec. 31, 2018
Regulated Operations [Abstract]
Schedule of Regulatory Assets and Liabilities	At December 31, 2018 , September 30, 2018 and September 30, 2017 , we recorded the following regulatory assets and liabilities on our balance sheets. These assets and liabilities will be recognized as revenues or expenses in future periods as they are reflected in customers’ rates. Regulatory Assets and Liabilities (In millions) Regulatory Assets Regulatory Liabilities Three Months Ended December 31, Fiscal Year Ended September 30, Three Months Ended December 31, Fiscal Year Ended September 30, 2018 2018 2017 2018 2018 2017 Current: Gas costs due from/to customers (a) $ 5.6 $ 4.4 $ 0.2 $ 46.9 $ 9.0 $ 10.6 Interruptible sharing (a) 0.4 — 2.4 1.7 1.5 0.7 Revenue normalization mechanisms for Maryland and Virginia (a) — — 11.7 3.6 3.6 1.4 Accelerated replacement recovery mechanisms (l) — 0.6 7.4 3.8 1.9 1.1 Rates subject to refund (c) — — — — — 9.0 Tax Cuts and Jobs Act rate refunds (d) — — — 19.2 18.1 — Total current $ 6.0 $ 5.0 $ 21.7 $ 75.2 $ 34.1 $ 22.8 Deferred: Accrued asset removal costs (m) $ — $ — $ — $ 264.6 $ 270.4 $ 292.2 Deferred gas costs (a)(b) 141.6 83.2 90.1 — — — Pension and other post-retirement benefits Deferred pension costs—trackers (e) 5.7 9.1 19.8 — — — ASC Topic 715 unrecognized costs/income (a)(f) Pensions 80.8 47.9 118.8 — — — Other post-retirement benefits — — — 121.3 159.2 134.2 Total pension and other post-retirement benefits 86.5 57.0 138.6 121.3 159.2 134.2 Other: Income tax-related amounts due from/to customers (g) 41.6 42.6 37.9 427.2 439.1 3.2 Losses/gains on issuance and extinguishments of debt and interest-rate derivative instruments (a)(h) 15.0 15.3 16.4 1.3 1.3 1.4 Rights-of-way fees (a) — — — 2.5 1.9 0.7 Business process outsourcing and related costs (a) 3.2 6.2 8.2 — — — Non-retirement employee benefits (a)(i) 15.6 16.5 17.8 — — — Deferred distribution integrity management (a)(j) 5.4 5.8 7.7 — — — Recoverable portion of abandoned liquid natural gas facility (a) 2.7 2.7 3.1 — — — Environmental response costs (a)(k) 5.8 5.0 2.5 — — — Energy efficiency program-Maryland (n) 3.4 4.5 5.3 — — — Other regulatory expenses (o) 6.4 5.5 5.6 0.9 1.4 4.1 Total other $ 99.1 $ 104.1 $ 104.5 $ 431.9 $ 443.7 $ 9.4 Total deferred $ 327.2 $ 244.3 $ 333.2 $ 817.8 $ 873.3 $ 435.8 Total $ 333.2 $ 249.3 $ 354.9 $ 893.0 $ 907.4 $ 458.6 (a) Washington Gas does not earn its overall rate of return on these assets. Washington Gas is allowed to recover and required to pay, using short-term interest rates, the carrying costs related to billed gas costs due from and to its customers in the District of Columbia and Virginia jurisdictions. (b) Includes fair value of derivatives, which are not included in customer bills until settled. (c) Represents provision established for refunds to customers when the substitution of final rates resulted in an amount greater than the amount collected during the interim period related to the 2016 Virginia Rate Case. (d) Represents amounts accrued for future refunds due to the Tax Cuts and Jobs Act of 2017. For a further discussion, see Rates and Regulatory Matters section of Management's Discussion Analysis and Note 8-Income Taxes in the Notes to Consolidated Financial Statements. (e) Relates to the District of Columbia jurisdiction. (f) Refer to Note 9-Pension and Other Post-Retirement Benefit Plans for a further discussion of these amounts. (g) This balance represents amounts due from customers for deferred tax liabilities related to tax benefits on deduction flowed directly to customers prior to the adoption of income tax normalization for ratemaking purposes and to tax rate changes including the latest reduction as a result of the Tax Act. (h) The losses or gains on the issuance and extinguishment of debt and interest-rate derivative instruments include unamortized balances from transactions executed in prior fiscal years. These transactions create gains and losses that are amortized over the remaining life of the debt as prescribed by regulatory accounting requirements. (i) Represents the timing difference between the recognition of workers compensation and short-term disability costs in accordance with generally accepted accounting principles and the way these costs are recovered through rates. (j) This balance represents amounts for deferred expenditures associated with Washington Gas’ Distribution Integrity Management Program (DIMP) in Virginia. (k) This balance represents allowed environmental remediation expenditures at Washington Gas sites to be recovered through rates for Maryland and the District of Columbia. The recovery period is over several years. (l) Balance represents amounts for deferred over or under collections of surcharges associated with Washington Gas' accelerated pipeline recovery programs in the District of Columbia, Maryland and Virginia. (m) Refer to Note 1-Accounting Policies for a further discussion of these amounts. (n) Balance represents amounts for deferred credits associated with Washington Gas' participation in the energy conservation and efficiency program EmPower in Maryland. (o) Balance primarily relates to the District of Columbia jurisdiction.

Accounts Payable and Other Ac_2

Accounts Payable and Other Accrued Liabilities (Tables)	3 Months Ended
	Dec. 31, 2018
Accounts Payable and Accrued Liabilities [Abstract]
Accounts Payable and Other Accrued Liabilities	The table below provides details for the amounts included in “Accounts payable and other accrued liabilities” on the balance sheets. December 31, September 30, (In millions) 2018 2018 2017 Accounts payable—trade $ 228.9 $ 187.0 $ 174.9 Employee benefits and payroll accruals 28.0 32.9 32.4 Other accrued liabilities 31.5 51.4 12.5 Total $ 288.4 $ 271.3 $ 219.8

Short-Term Debt (Tables)

Short-Term Debt (Tables)	3 Months Ended
	Dec. 31, 2018
Short-term Debt [Abstract]
Commited Credit Available	The following is a summary of committed credit available at December 31, 2018 , September 30, 2018 and September 30, 2017 . Committed Credit Available ($ in millions) December 31, 2018 September 30, 2018 September 30, 2017 Committed credit agreements Unsecured revolving credit facility, expires December 19, 2019 (a) $350.0 $350.0 $350.0 Less: Commercial Paper (296.0) (95.0) (123.0) Net committed credit available $54.0 $255.0 $227.0 Weighted average interest rate 2.93% 2.42% 1.22% (a) Washington Gas has the right to request extensions with the banks’ approval. Washington Gas’ revolving credit facility permits it to borrow an additional $100 million , with the banks’ approval, for a total of $450 million .

Long Term Debt (Tables)

Long Term Debt (Tables)	3 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Long term debt outstanding	The following tables show the outstanding notes with maturities in calendar years as of December 31, 2018 , and maturities in fiscal years as of September 30, 2018 and September 30, 2017 . Long Term Debt Outstanding December 31, 2018 ($ In millions) Due calendar year 2019, 4.76% $ 50.0 Due calendar year 2023, 6.65% 20.0 Due calendar year 2025, 5.44% 40.5 Due calendar year 2026, 6.62% to 6.82% 53.0 Due calendar year 2027, 6.40% to 6.57% 72.0 Due calendar year 2028, 6.57% to 6.85% 52.0 Due calendar year 2030, 7.50% 8.5 Due calendar year 2036, 5.70% to 5.78% 50.0 Due calendar year 2040, 5.21% 75.0 Due calendar year 2043, 5.00% 75.0 Due calendar year 2044, 4.22% to 4.24% 150.0 Due calendar year 2046, 3.80% 450.0 Total Long-Term Debt (a) $ 1,096.0 Unamortized discount (2.9 ) Unamortized debt expense (8.1 ) Less—current maturities 50.0 Total Long-Term Debt $ 1,035.0 Weighted average interest rate (b) 4.77 % (a) Includes MTNs and private placement notes. The amount represents face value of long-term debt including current maturities. (b) Weighted average interest rate is for the long-term debt including current maturities . Long Term Debt Outstanding September 30, ($ In millions) 2018 2017 Due fiscal year 2019, 7.46% $ 50.0 50.0 Due fiscal year 2020, 4.76% 50.0 50.0 Due fiscal year 2023, 6.65% 20.0 20.0 Due fiscal year 2025, 5.44% 40.5 40.5 Due fiscal year 2027, 6.40% to 6.82% 125.0 125.0 Due fiscal year 2028, 6.57% to 6.85% 52.0 52.0 Due fiscal year 2030, 7.50% 8.5 8.5 Due fiscal year 2036, 5.70% to 5.78% 50.0 50.0 Due fiscal year 2041, 5.21% 75.0 75.0 Due fiscal year 2044, 4.22% to 5.00% 175.0 175.0 Due fiscal year 2045, 4.24% 50.0 50.0 Due fiscal year 2046, 3.80% 450.0 450.0 Total Long-Term Debt (a) $ 1,146.0 1,146.0 Unamortized discount (2.9 ) (3.0 ) Unamortized debt expense (8.1 ) (8.5 ) Less—current maturities 50.0 — Total Long-Term Debt $ 1,085.0 1,134.5 Weighted average interest rate (b) 4.89 % 4.89 % (a) Includes MTNs and private placement notes. The amount represents face value of long-term debt including current maturities. (b) Weighted average interest rate is for the long-term debt including current maturities.
Schedule of Long-term Debt Instruments [Table Text Block]	The following table shows long-term debt issuances and retirements for the three months ended December 31, 2018 , and fiscal year ended September 30, 2017. There were no issuances or retirements during the fiscal year ended September 30, 2018. Long-Term Debt Issuances and Retirements ($ In millions) Principal (a) Interest Rate (b) Effective Cost (b) Nominal Maturity Date Three Months Ended December 31, 2018 Retirements: 12/05/2018 $ 50.0 7.46 % 7.46 % 12/5/2018 Total $ 50.0 Year ended September 30, 2017 Issuances: 9/18/2017 $ 200.0 3.80 % 9/15/2046 Total $ 200.0 (a) Represents face amount of notes. (b) Represents the interest rate and effective cost at the trade date of the debt.

Preferred Stock (Tables)

Preferred Stock (Tables)	3 Months Ended
	Dec. 31, 2018
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock Table	The following table presents this information, as well as call prices for each preferred stock series outstanding. Preferred Stock Preferred Liquidation Preference Series Shares Per Share Call Price Outstanding Outstanding Involuntary Voluntary Per Share $4.80 150,000 $100 $101 $101 $4.25 70,600 $100 $105 $105 $5.00 60,000 $100 $102 $102

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Components of Income Tax Expense	The following tables provide the components of income tax expenses for the three months ended December 31, 2018 and for fiscal years ended September 30, 2018, 2017 and 2016. Components of Income Tax Expense (Benefit) Three Months Ended December 31, Fiscal Years Ended September 30, (In thousands) 2018 2018 2017 2016 INCOME TAX EXPENSE Current: Federal $ — $ — $ 1,722 $ (48,064 ) State — 1,274 1,283 (2,957 ) Total current — 1,274 3,005 (51,021 ) Deferred: Federal Accelerated depreciation 6,494 (27,846 ) 83,009 93,385 Other 2,537 (8,485 ) (18,419 ) 13,826 State Accelerated depreciation 2,416 12,533 15,033 13,081 Other (3,435 ) (2,637 ) (2,037 ) 3,190 Total deferred (a) 8,012 (26,435 ) 77,586 123,482 Amortization of investment tax credits (165 ) (702 ) (751 ) (795 ) Total income tax expense (benefit) $ 7,847 $ (25,863 ) $ 79,840 $ 71,666 (a) Includes tax expense of $ 1.2 million and $ 7.0 million related to re-measurement of deferred income taxes for the three months ended December 31, 2018 and the fiscal year ended September 30, 2018, respectively.
Reconciliation Between the Statutory Federal Income Tax Rate and Effective Tax Rate	The effective income tax rate from continuing operations varies from the U.S. Federal statutory rate principally due to the following: Reconciliation Between the Statutory Federal Income Tax Rate and Effective Tax Rate Three Months Ended December 31, Fiscal Years Ended September 30, ($ In thousands) 2018 2018 2017 2016 Income taxes at statutory federal income tax rate (a) $ 11,974 21.00 % $ (11,026 ) 21.00 % $ 74,071 35.00 % $ 64,673 35.00 % Increase (decrease) in income taxes resulting from: — Plant basis differences (4,261 ) (7.47 ) 1,079 (2.06 ) 2,213 1.05 2,445 1.32 Allowance for funds used during construction (520 ) (0.91 ) (70 ) 0.13 (291 ) (0.14 ) (509 ) (0.28 ) Amortization of investment tax credits (165 ) (0.29 ) (703 ) 1.34 (751 ) (0.35 ) (795 ) (0.43 ) Amortization of excess deferred taxes (2,431 ) (4.26 ) (9,798 ) 18.66 (196 ) (0.09 ) — — Cost of removal (28 ) (0.05 ) (1,561 ) 2.97 (2,944 ) (1.39 ) (3,722 ) (2.01 ) State income taxes-net of federal benefit 2,737 4.80 (2,659 ) 5.06 9,482 4.48 8,310 4.50 Consolidated tax sharing allocation — — — — — — 1,073 0.58 Re-measurement 1,243 2.18 7,031 (13.39 ) — — — — ASU 2016-09 adoption — — (3,223 ) 6.14 — — — — Return to provision adjustment — — (4,669 ) 8.89 (4,859 ) (2.30 ) (1,353 ) (0.73 ) Other items-net (702 ) (1.23 ) (264 ) 0.50 3,115 1.47 1,544 0.84 Total income tax expense (benefit) and effective tax rate $ 7,847 13.77 % $ (25,863 ) 49.24 % $ 79,840 37.73 % $ 71,666 38.79 % (a) As a result of the merger with AltaGas, Washington Gas is subject to two separate short periods and accompanying returns. The first period through July 6, 2018 is subjected to a higher, blended federal statutory rate. Due to the net operating loss for federal tax purposes through September 30, 2018, all the year activity is ultimately taxed at 21%. As such, for presentational purposes, we applied a 21% rate to the entire fiscal year 2018 activity.
Components of Deferred Income Tax Assets (Liabilities)	The following table provides the components of accumulated deferred income tax assets (liabilities) for Washington Gas at December 31, 2018, September 30, 2018 and September 30, 2017. Components of Accumulated Deferred Income Tax Assets (Liabilities) (In thousands) December 31, 2018 September 30, 2018 September 30, 2017 Deferred income tax assets: Pensions $ 25,629 $ 43,071 $ 41,907 Uncollectible accounts 1,680 1,131 7,815 Inventory overheads 4,088 4,090 6,617 Employee compensation and benefits 40,960 51,006 47,479 Derivatives 8,737 7,435 11,187 Income taxes recoverable through future rates 96,256 121,357 — Deferred gas costs — — 1,485 Net operating loss 84,674 90,943 — Total assets 262,024 319,033 116,490 Deferred income tax liabilities: Other post-retirement benefits 63,540 106,289 89,494 Accelerated depreciation and other plant related items 636,196 615,499 876,235 Losses/gains on reacquired debt 571 581 1,047 Income taxes recoverable through future rates — — 33,324 Deferred gas costs 14,928 3,041 — Other 1,037 3,430 4,775 Total liabilities 716,272 728,840 1,004,875 Net accumulated deferred income tax assets (liabilities) (454,248 ) $ (409,807 ) $ (888,385 )
Unrecognized Tax Benefits	The following table summarizes the change in unrecognized tax benefits during the three months ended December 31, 2018, and the fiscal years of 2018, 2017, 2016, and our total unrecognized tax benefits at December 31, 2018 under the provisions of ASC Topic 740, Income Taxes: Unrecognized Tax Benefits For Fiscal Year Ended September 30, Three Months Ended December 31, Fiscal Year Ended September 30 (In thousands) 2018 2018 2017 2016 Total unrecognized tax benefits at beginning of the period $ 43,567 $ 48,009 $ 42,283 $ 38,627 Increases in tax positions relating to current period 2,574 10,947 10,766 10,645 Decreases in tax positions relating to prior periods (10,235 ) (15,389 ) (5,040 ) (6,989 ) Total unrecognized tax benefits at end of the period $ 35,906 $ 43,567 $ 48,009 $ 42,283

Pension and Other Post-Retire_2

Pension and Other Post-Retirement Benefit Plans (Tables)	3 Months Ended
	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Post Retirement Benefits	The following table provides certain information about Washington Gas’ post-retirement benefits: Post-Retirement Benefits Pension Benefits (a) Health and Life Benefits Three Months Ended December 31, Fiscal Year Ended September 30, Three Months Ended December 31, Fiscal Year Ended September 30, (In millions) 2018 2018 2017 2018 2018 2017 Change in projected benefit obligation (b) Benefit obligation at beginning of period $ 989.8 $ 1,047.5 $ 1,069.3 $ 283.3 $ 309.0 $ 324.3 Service cost 3.0 14.9 16.5 1.3 5.3 5.8 Interest cost 10.6 39.6 38.4 3.0 11.7 11.7 Change in plan benefits 0.2 — — — — 1.1 Actuarial loss (gain) (17.3 ) (65.2 ) (28.2 ) (6.2 ) (28.7 ) (18.9 ) Retiree contributions and rebates — — — 0.9 1.9 1.8 Benefits paid (14.5 ) (47.0 ) (48.5 ) (4.4 ) (15.9 ) (16.8 ) Projected benefit obligation at end of period (b) $ 971.8 $ 989.8 $ 1,047.5 $ 277.9 $ 283.3 $ 309.0 Change in plan assets Fair value of plan assets at beginning of period $ 863.9 $ 872.5 $ 850.0 $ 569.3 $ 540.5 $ 505.0 Actual return on plan assets (42.3 ) 38.8 68.6 (32.0 ) 43.0 48.1 Company contributions 0.4 1.8 4.4 1.3 5.0 8.2 Retiree contributions and rebates — — — 0.9 1.9 1.8 Expenses (0.5 ) (2.2 ) (2.0 ) (6.3 ) (5.2 ) (5.8 ) Benefits paid (14.5 ) (47.0 ) (48.5 ) (4.4 ) (15.9 ) (16.8 ) Fair value of plan assets at end of period $ 807.0 $ 863.9 $ 872.5 $ 528.8 $ 569.3 $ 540.5 Funded status at end of period $ (164.8 ) $ (125.9 ) $ (175.0 ) $ 250.9 $ 286.0 $ 231.5 Allocation to affiliates $ (1.6 ) $ (1.3 ) $ (1.7 ) $ 1.4 $ 1.7 $ 1.2 Adjusted funded status at end of period (163.2 ) (124.6 ) (173.3 ) 249.5 284.3 230.3 Total amounts recognized on balance sheet Non-current asset $ — $ — $ — $ 249.5 $ 284.3 $ 230.3 Current liability (20.2 ) (20.2 ) (6.5 ) — — — Non-current liability (143.0 ) (104.4 ) (166.8 ) — — — Total recognized $ (163.2 ) $ (124.6 ) $ (173.3 ) $ 249.5 $ 284.3 $ 230.3 (a) The DB SERP and DB Restoration, included in pension benefits in the table above, does not include the amounts funded in rabbi trust. (b) For the Health and Life Benefits, the change in projected benefit obligation represents the accumulated benefit obligation.
Projected and accumulated benefit obligation	The following table provides the projected benefit obligation (PBO) and accumulated benefit obligation (ABO) for the qualified pension plan, DB SERP and DB Restoration at December 31, 2018 , September 30, 2018 and September 30, 2017 . Projected and accumulated benefit obligation Qualified Pension Plan DB SERP DB Restoration December 31, September 30, December 31, September 30, December 31, September 30, (In millions) 2018 2018 2017 2018 2018 2017 2018 2018 2017 Projected benefit obligation $ 906.2 $ 923.6 $ 983.1 $ 61.5 $ 62.2 $ 60.2 $ 4.1 $ 4.0 $ 4.2 Accumulated benefit obligation $ 847.1 $ 859.1 $ 905.8 $ 59.8 $ 60.7 $ 57.5 $ 3.2 $ 3.0 $ 3.0
Unrecognized Costs Income Recorded On Balance Sheet	The following table provides amounts recorded to regulatory assets, regulatory liabilities and accumulated other comprehensive loss/(income) at December 31, 2018 , September 30, 2018 and September 30, 2017 : Unrecognized Costs/Income Recorded on the Balance Sheet Pension Benefits Health and Life Benefits December 31, September 30, December 31, September 30, (In millions) 2018 2018 2017 2018 2018 2017 Actuarial net loss (gain) $ 96.1 $ 61.0 $ 136.1 $ (26.0 ) $ (64.5 ) $ (21.8 ) Prior service cost (credit) 1.0 0.9 1.2 (102.8 ) (107.2 ) (124.9 ) Total (a) $ 97.1 $ 61.9 $ 137.3 $ (128.8 ) $ (171.7 ) $ (146.7 ) Regulatory asset (liability) (b) $ 80.8 $ 47.9 $ 118.8 $ (121.1 ) $ (159.4 ) $ (136.4 ) Pre-tax accumulated other comprehensive loss (income) (c) 15.9 13.7 17.7 (6.9 ) (11.2 ) (9.5 ) Total $ 96.7 $ 61.6 $ 136.5 $ (128.0 ) $ (170.6 ) $ (145.9 ) (a) Pension benefits include amounts allocated to affiliates of $ 0.4 million , $ 0.3 million and $ 0.8 million at December 31, 2018, September 30, 2018 and 2017, respectively; Health and Life Benefits includes amounts allocated to affiliates of $ 0.8 million , $ 1.1 million , and $ 0.8 million at December 31, 2018, September 30, 2018 and 2017, respectively. (b) The regulatory liability recorded on our balance sheet at September 30, 2018 and September 30, 2017 is net of a deferred income tax benefit of $ 0.2 million and $2.2 million , respectively. There is no deferred income tax benefit at December 31, 2018. (c) The total amount of accumulated other comprehensive loss recorded on our balance sheets at December 31, 2018 , September 30, 2018 and September 30, 2017 is net of an income tax benefit of $ 2.4 million , $0.7 million and $3.6 million , respectively.
Amount Recognized During Current Year	The following table provides amounts that are included in regulatory assets/liabilities and accumulated other comprehensive loss associated with our unrecognized pension and other post-retirement benefit costs that were recognized as components of net periodic benefit cost before allocations to affiliates and capital during the three months ending December 31, 2018 and the fiscal year ended September 30, 2018 . Amounts Recognized During the Three Months Ended December 31, 2018 Regulatory assets/liabilities Accumulated other (In millions) Pension Health and Pension Health and Actuarial net loss $ 1.0 $ — $ 0.4 $ — Prior service cost (credit) 0.1 (4.1 ) — (0.3 ) Total $ 1.1 $ (4.1 ) $ 0.4 $ (0.3 )
Amount Recognized During Next Fiscal Year	The following table provides amounts that are included in regulatory assets/liabilities and accumulated other comprehensive loss associated with our unrecognized pension and other post-retirement benefit costs that are expected to be recognized as components of net periodic benefit cost before allocations to affiliates and capital during 2019 . Amounts to be Recognized During Calendar Year 2019 Regulatory assets/liabilities Accumulated other comprehensive loss (In millions) Pension Benefits Health and Life Benefits Pension Benefits Health and Life Benefits Actuarial net loss $ 3.4 $ — $ 1.7 $ — Prior service cost (credit) 0.1 (15.0 ) 0.2 (0.8 ) Total $ 3.5 $ (15.0 ) $ 1.9 $ (0.8 )
Components of Net Periodic Benefit Costs (Income)	The components of the net periodic benefit costs (income) for three months ended December 31, 2018 , and the years ended September 30, 2018, 2017 and 2016 related to pension and other post-retirement benefits were as follows: Components of Net Periodic Benefit Costs (Income) Pension Benefits Health and Life Benefits Three months ended December 31, Year Ended September 30, Three months ended December 31, Year Ended September 30, (In millions) 2018 2018 2017 2016 2018 2018 2017 2016 Service cost $ 3.0 $ 14.9 $ 16.5 $ 14.2 $ 1.3 $ 5.3 $ 5.8 $ 4.6 Interest cost 10.6 39.6 38.4 41.3 3.0 11.7 11.7 13.1 Expected return on plan assets (10.9 ) (42.3 ) (41.0 ) (40.9 ) (6.1 ) (23.7 ) (22.1 ) (20.4 ) Recognized prior service cost (credit) 0.1 0.3 0.3 0.3 (4.4 ) (17.6 ) (17.7 ) (17.7 ) Recognized actuarial loss 1.4 15.6 22.0 16.9 — — 1.9 1.2 Net periodic benefit cost (income) 4.2 28.1 36.2 31.8 (6.2 ) (24.3 ) (20.4 ) (19.2 ) Allocation to affiliates (0.4 ) (4.2 ) (2.9 ) (1.9 ) 0.8 3.1 1.4 1.1 Adjusted net periodic benefit cost (income) 3.8 23.9 33.3 29.9 (5.4 ) (21.2 ) (19.0 ) (18.1 ) Amount allocated to construction projects (a) (0.6 ) (4.7 ) (6.4 ) (5.6 ) (0.2 ) 4.0 4.6 4.1 Amount deferred as regulatory asset (liability)-net allocations 1.5 5.9 6.9 7.1 — — — (0.2 ) Amount charged (credited) to expense $ 4.7 $ 25.1 $ 33.8 $ 31.4 $ (5.6 ) $ (17.2 ) $ (14.4 ) $ (14.2 )
Benefit Obligations Assumptions/Net Periodic Benefits Assumptions	The weighted average assumptions used to determine net periodic benefit obligations and net periodic benefit costs were as follows: Benefit Obligations Assumptions Pension Benefits Health and Life Benefits Three months ended December 31, Fiscal Year ended September 30, Three months ended December 31, Fiscal Year ended September 30, 2018 2018 2017 2016 2018 2018 2017 2016 Discount rate (a) 4.30%-4.40% 4.30%-4.40% 3.60%-3.90% 3.40%-3.70% 4.40 % 4.40 % 3.90 % 3.70 % Rate of compensation increase 3.50%-4.10% 3.50%-4.10% 3.50%-4.10% 3.50%-4.10% 4.10 % 4.10 % 4.10 % 4.10 % (a) The increase in the discount rate in the three months ended December 31, 2018 and fiscal year 2018 compared to prior years primarily reflects the increase in long-term interest rates. Net Periodic Benefit Cost Assumptions Pension Benefits Health and Life Benefits Three months ended December 31, Year ended September 30, Three months ended December 31, Year ended September 30, 2018 2018 2017 2016 2018 2018 2017 2016 Discount rate (a) 4.30%-4.40% 3.60%-3.90% 3.40%-3.70% 4.10%-4.50% 4.40 % 3.90 % 3.70 % 4.50 % Expected long-term return on plan assets (b) 5.75 % 5.75 % 5.75 % 6.00 % 5.25 % 5.50 % 5.50 % 5.75 % Rate of compensation increase (c) 3.50%-4.10% 3.50%-4.10% 3.50%-4.10% 3.50%-4.10% 4.10 % 4.10 % 4.10 % 4.10 % (a) The changes in the discount rates over the last three fiscal years primarily reflect the changes in long-term interest rates. (b) For health and life benefits, the expected returns for certain funds may be lower due to certain portions of income that are subject to an assumed income tax rate of 42.2% . (c) The changes in the rate of compensation reflects the best estimates of actual future compensation levels including consideration of general price levels, productivity, seniority, promotion, and other factors su
Healthcare Trends	Healthcare Trend (In millions) One Percentage-Point Increase One Percentage-Point Decrease Increase (decrease) total service and interest cost components $ 0.2 $ (0.1 ) Increase (decrease) post-retirement benefit obligation $ 5.2 $ (4.6 )
Expected Benefit Payments	Expected benefit payments, including benefits attributable to estimated future employee service, which are expected to be paid over the next ten calendar years are as follows: Expected Benefit Payments (In millions) Pension Benefits Health and Life Benefits 2019 $ 67.5 $ 16.3 2020 53.4 15.7 2021 54.6 15.8 2022 57.7 15.9 2023 56.1 15.9 2024—2028 291.2 81.1
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Pension and OPEB Plan Assets	The following tables present the fair value of the pension plan assets and health and life insurance plan assets by asset category as of December 31, 2018 , September 30, 2018 and September 30, 2017 . Pension Plan Assets % of ($ In millions) Level 1 Level 2 Level 3 Total Total At December 31, 2018 Cash and cash equivalents $ 0.7 $ — $ — $ 0.7 0.1 % Equity securities Preferred Securities — 1.9 — 1.9 0.2 Fixed income securities U.S. Treasuries — 133.2 — 133.2 16.5 U.S. Corporate Debt — 216.4 — 216.4 26.8 U.S. Agency Obligations and Government Sponsored Entities — 27.5 — 27.5 3.4 Asset-Backed Securities — 0.5 — 0.5 0.1 Municipalities — 8.3 — 8.3 1.0 Non-U.S. Corporate Debt — 46.7 — 46.7 5.8 Other (a) — 4.9 — 4.9 0.6 Mutual Funds (b) 36.4 — — 36.4 4.5 Derivatives (c) — 6.8 — 6.8 0.8 Total investments in the fair value hierarchy $ 37.1 $ 446.2 $ — $ 483.3 59.8 % Investments measured at net asset value using the NAV practical expedient (d) Commingled Funds and Pooled Separate Accounts (e) 289.6 35.9 % Private Equity/Limited Partnership (f) 35.3 4.4 % Total fair value of plan investments 808.2 100.1 % Net receivable (payable) (g) (1.2 ) (0.1 ) Total plan assets at fair value (h) $ 807.0 100.0 % Pension Plan Assets % of ($ In millions) Level 1 Level 2 Level 3 Total Total At September 30, 2018 Cash and cash equivalents $ 2.2 $ — $ — $ 2.2 0.3 % Equity securities Preferred Securities — 2.1 — 2.1 0.2 Fixed income securities U.S. Treasuries — 127.6 — 127.6 14.8 U.S. Corporate Debt — 227.8 — 227.8 26.4 U.S. Agency Obligations and Government Sponsored Entities — 28.3 — 28.3 3.3 Asset-Backed Securities — 0.5 — 0.5 0.1 Municipalities — 8.3 — 8.3 1.0 Non-U.S. Corporate Debt — 47.1 — 47.1 5.5 Other (a) — 5.2 — 5.2 0.6 Mutual Funds (b) 42.4 — — 42.4 4.9 Derivatives (c) — 1.1 — 1.1 0.1 Total investments in the fair value hierarchy $ 44.6 $ 448.0 $ — $ 492.6 57.2 % Investments measured at net asset value using the NAV practical expedient (d) Commingled Funds and Pooled Separate Accounts (e) 329.3 38.0 % Private Equity/Limited Partnership (f) 39.1 4.5 % Total fair value of plan investments 861.0 99.7 % Net receivable (g) 2.9 0.3 Total plan assets at fair value (i) $ 863.9 100.0 % Pension Plan Assets % of ($ In millions) Level 1 Level 2 Level 3 Total Total At September 30, 2017 Cash and cash equivalents $ 0.7 $ — $ — $ 0.7 0.1 % Equity securities Preferred Securities — 0.6 — 0.6 0.1 Fixed income securities U.S. Treasuries — 140.9 — 140.9 16.2 U.S. Corporate Debt — 232.3 — 232.3 26.6 U.S. Agency Obligations and Government Sponsored Entities — 20.0 — 20.0 2.3 Asset-Backed Securities — 2.0 — 2.0 0.2 Municipalities — 14.9 — 14.9 1.7 Non-U.S. Corporate Debt — 48.1 — 48.1 5.5 Repurchase Agreement (i) 3.7 3.7 0.4 Other (a) — 6.7 — 6.7 0.8 Mutual Funds (b) 41.4 — — 41.4 4.7 Derivatives (c) — 1.9 — 1.9 0.2 Total investments in the fair value hierarchy $ 42.1 $ 471.1 $ — $ 513.2 58.8 % Investments measured at net asset value using the NAV practical expedient (d) Commingled Funds and Pooled Separate Accounts (e) $ 324.4 37.2 % Private Equity/Limited Partnership (f) $ 37.6 4.3 % Total fair value of plan investments 875.2 100.3 % Net payable (g) (2.7 ) (0.3 ) Total plan assets at fair value $ 872.5 100.0 % (a) This category primarily includes non-U.S. government bonds as of December 31, 2018 and September 30, 2018 and 2017 . (b) At December 31, 2018 and September 30, 2018 and 2017 , the investment in a mutual fund consisted primarily of common stock of non-U.S. based companies. (c) At December 31, 2018 and September 30, 2018 and 2017 , this category included a combination of long-term U.S. Treasury interest rate future contracts, currency forwards, currency option interest rate swaps, and put and call options on both interest rate swaps and credit default swap index products. (d) In accordance with ASC Topic 820, these investments are measured at fair value using NAV per share as a practical expedient and, therefore, have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliations of the fair value hierarchy to the statements of net assets available for plan benefits. (e) As of December 31, 2018 investments in commingled funds and a pooled separate account consisted of approximately 89% common stock U.S companies; 9% income producing properties located in the United States; and 1% short-term money market investments. As of September 30, 2018 and 2017 , investments in commingled funds and a pooled separate account consisted of approximately 90% common stock U.S companies; 8% income producing properties located in the United States; and 2% short-term money market investments. (f) At December 31, 2018 and September 30, 2018 and 2017 , investments in a private equity/limited partnership consisted of common stock of international companies. (g) At December 31, 2018 and September 30, 2018 and 2017 , this net payable primarily represents pending trades for investments purchased net of pending trades for investments sold and interest receivable. (h) This table does not include rabbi trust investments located in "Current Assets-Other" and "Deferred Charges and Other Assets-Other" on our balance sheets. Refer to
Other post-retirement benefits
Defined Benefit Plan Disclosure [Line Items]
Pension and OPEB Plan Assets	Healthcare and Life Insurance Plan Assets % of ($ In millions) Level 1 Level 2 Level 3 Total Total At September 30, 2018 Cash and Cash Equivalents $ 2.9 $ — $ — $ 2.9 0.5 % Fixed Income Securities U.S Agency Obligations — 1.9 — 1.9 0.3 U.S. Treasuries — 50.1 — 50.1 8.8 U.S. Corporate Debt — 55.0 — 55.0 9.7 Municipalities — 4.7 — 4.7 0.8 Non-U.S. Corporate Debt — 9.1 — 9.1 1.6 Other (a) — 3.4 — 3.4 0.6 Total investments in the fair value hierarchy $ 2.9 $ 124.2 $ — $ 127.1 22.3 % Investments measured at net asset value using the NAV practical expedient (b) Commingled Funds (c) 441.6 77.6 % Total fair value of plan investments 568.7 99.9 % Net receivable (d) 0.6 0.1 Total plan assets at fair value $ 569.3 100.0 % At September 30, 2017 Cash and Cash Equivalents $ 2.6 $ — $ — $ 2.6 0.5 % Fixed Income Securities U.S Agency Obligations — 1.7 — 1.7 0.3 U.S. Treasuries — 36.0 — 36.0 6.7 U.S. Corporate Debt — 41.9 — 41.9 7.8 Municipalities — 3.6 — 3.6 0.7 Non-U.S. Corporate Debt — 7.2 — 7.2 1.3 Other (a) — 2.8 — 2.8 0.5 Total investments in the fair value hierarchy $ 2.6 $ 93.2 $ — $ 95.8 17.8 % Investments measured at net asset value using the NAV practical expedient (b) Commingled Funds (c) 444.0 82.1 % Total fair value of plan investments 539.8 99.9 % Net receivable (d) 0.7 0.1 Total plan assets at fair value $ 540.5 100.0 % (a) At December 31, 2018 and September 30, 2018 and 2017 , this category consisted primarily of non-U.S. government bonds. (b) In accordance with ASC Topic 820, these investments are measured at fair value using Net Asset Value (NAV) per share as a practical expedient and, therefore, have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliations of the fair value hierarchy to the statements of net assets available for plan benefits. (c) At December 31, 2018, investments held by commingled funds in which the plan invests consisted of 54% of common stock of large-cap U.S. companies, 20% of US Govt fixed income securities and 26% corporate bonds. At September 30, 2018, investments held by commingled funds in which the plan invests consisted primarily of 58% of common stock of large-cap U.S. companies, 17% of U.S. Government fixed income securities and 25% of corporate bonds. At September 30, 2017 , investments held by commingled funds in which the plan invests consisted primarily of 67% of common stock of large-cap U.S. companies, 13% of U.S. Government fixed income securities and 20% of corporate bonds. (d) At December 31,2018 and September 30, 2018 and 2017 , this net receivable primarily represents pending trades for investments sold and interest receivable net of pending trades for investments purchased.

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Performance Unit Activity	The following tables summarize information regarding performance unit and restricted unit activity during the three months ended December 31, 2018 . Performance Unit Activity Three Months Ended December 31, 2018 Number of Units Non-vested and outstanding, beginning of the quarter — Granted 5,934,828 Settled — Canceled/forfeited — Non-vested and outstanding, end of year 5,934,828
Restricted unit activity	Restricted Unit Activity Three Months Ended December 31, 2018 Number of Units Non-vested and outstanding, beginning of the quarter — Granted 2,253,585 Settled — Canceled/forfeited — Non-vested and outstanding, end of year 2,253,585

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	Minimum future rental payments under operating leases over the next five calendar years and thereafter are as follows: Minimum Payments Under Operating Leases (a) (In millions) 2019 $ 3.0 2020 5.7 2021 5.3 2022 5.3 2023 5.4 Thereafter 50.8 Total $ 75.5 (a) During the year 2018, we moved our headquarter to the office located at 1000 Maine Ave., S.W. Washington, D.C. The operating lease of the previous office located at 101 Constitution Ave., N.W. Washington, D.C. ended in August 2018.
Long-term Purchase Commitment	The following table summarizes the minimum contractual payments that Washington Gas will make under its pipeline transportation, storage and peaking contracts, as well as minimum contractual payments to purchase natural gas at prices based on market conditions during the next five calendar years and thereafter. Washington Gas Contract Minimums (In millions) Pipeline Contracts (a) Gas Purchase Commitments (b) 2019 $ 373.1 $ 459.2 2020 374.1 384.8 2021 366.3 362.0 2022 362.6 353.9 2023 362.1 339.4 Thereafter 1,209.6 2,695.7 Total $ 3,047.8 $ 4,595.0 (a) Represents minimum payments for natural gas transportation, storage and peaking contracts that have expiration dates through calendar year 2044 . (b) Includes known and reasonably likely commitments to purchase natural gas. Cost estimates are based on forward market prices at December 31, 2018 .

Derivative and Weather Relate_3

Derivative and Weather Related Instruments (Tables)	3 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Absolute Notional Amounts of Open Positions on Derivative Instruments	The following table presents the balance sheet classification for all derivative instruments as of December 31, 2018 , September 30, 2018 and September 30, 2017 . Absolute Notional Amounts of Open Positions on Derivative Instruments Derivative transactions Notional Amounts December 31, 2018 December 31, 2018 September 30, 2018 September 30, 2017 Natural Gas (In millions of therms) Asset optimization & trading 13,051.0 13,580.0 11,223.0 Other risk-management activities 1,072.0 1,066.0 1,181.0
Balance Sheet Classification of Derivative Instruments	The following table presents the balance sheet classification for all derivative instruments as of December 31, 2018 , September 2018 and September 2017 . Balance Sheet Classification of Derivative Instruments (b) (In millions) As of December 31, 2018 Gross Gross Netting of Total (a) Current Assets—Derivatives $ 25.7 $ (6.2 ) $ — $ 19.5 Deferred Charges and Other Assets—Derivatives 11.3 — — 11.3 Current Liabilities—Derivatives 1.1 (21.4 ) (20.3 ) Deferred Credits—Derivatives — (116.8 ) — (116.8 ) Total $ 38.1 $ (144.4 ) $ — $ (106.3 ) As of September 30, 2018 Current Assets—Derivatives $ 17.8 $ (0.4 ) $ — $ 17.4 Deferred Charges and Other Assets—Derivatives 8.7 — — 8.7 Current Liabilities—Derivatives 2.6 (20.2 ) 2.8 (14.8 ) Deferred Credits—Derivatives (1.6 ) (102.6 ) — (104.2 ) Total $ 27.5 $ (123.2 ) $ 2.8 $ (92.9 ) As of September 30, 2017 Current Assets—Derivatives $ 7.5 $ (2.4 ) $ — $ 5.1 Deferred Charges and Other Assets—Derivatives 16.5 (0.3 ) — 16.2 Current Liabilities—Derivatives — (30.3 ) — (30.3 ) Deferred Credits—Derivatives — (112.3 ) — (112.3 ) Total $ 24.0 $ (145.3 ) $ — $ (121.3 ) (a) Washington Gas has elected to offset the fair value of recognized derivative instruments against the right to reclaim or the obligation to return collateral for derivative instruments executed under the same master netting arrangement in accordance with ASC Topic 815. All recognized derivative contracts and associated financial collateral subject to a master netting arrangement or similar that is eligible for offset under ASC Topic 815 have been presented net in the balance sheet. (b) Washington Gas did not have derivative instruments outstanding that were designated as hedging instruments at December 31, 2018 , September 30, 2018, or September 30, 2017 .
Gains and (Losses) on Derivative Instruments	The following tables present all gains and losses associated with derivative instruments for the three months ended December 31, 2018 , and the fiscal years ended September 30, 2018, 2017 and 2016 . Washington Gas Light Company Gains and (Losses) on Derivative Instruments (In millions) Three Months Ended December 31, Fiscal Year Ended September 30, 2018 2018 2017 2016 Recorded to income Utility cost of gas (3.2 ) (2.1 ) 50.1 12.1 Recorded to regulatory assets Gas costs (6.0 ) (7.6 ) 77.2 13.9 Other (a) — — — (7.3 ) Total $ (9.2 ) $ (9.7 ) $ 127.3 $ 18.7 (a) Represents the settlement of Washington Gas' forward starting interest rate swap in September 2016.
Collateral Not Offset Against Derivative Assets and Liabilities	The table below presents collateral not offset against derivative assets and liabilities at December 31, 2018 , September 30, 2018, and September 30, 2017 , respectively. Collateral Not Offset Against Derivative Assets and Liabilities (In millions) Collateral deposits posted with counterparties Cash collateral held representing an obligation December 31, 2018 $ 7.4 $ 0.2 September 30, 2018 10.6 2.7 September 30, 2017 $ 3.7 $ 0.1
Potential Collateral Requirements for Derivative Liabilities with Credit-Risk-Contingent Features	The following table shows the aggregate fair value of all derivative instruments with credit-related contingent features that are in a liability position, as well as the maximum amount of collateral that would be required if the most intrusive credit-risk-related contingent features underlying these agreements were triggered on December 31, 2018, September 30, 2018 and September 30, 2017, respectively. Potential Collateral Requirements for Derivative Liabilities with Credit-Risk-Contingent Features (In millions) December 31, 2018 Derivative liabilities with credit-risk-contingent features $ 1.1 Maximum potential collateral requirements 1.0 September 30, 2018 Derivative liabilities with credit-risk-contingent features $ 0.4 Maximum potential collateral requirements $ 0.4 September 30, 2017 Derivative liabilities with credit-risk-contingent features $ 2.8 Maximum potential collateral requirements 2.8

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements Under the Fair Value Hierarchy	The following tables set forth financial instruments recorded at fair value as of December 31, 2018 , September 30, 2018 and September 30, 2017 , respectively. A financial instrument’s classification within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement requires judgment and may affect the valuation of fair value assets and liabilities and their placement within the fair value hierarchy. Fair Value Measurements Under the Fair Value Hierarchy (In millions) Level 1 Level 2 Level 3 Total At December 31, 2018 Assets Natural gas related derivatives $ — $ 9.8 $ 28.3 $ 38.1 Total Assets $ — $ 9.8 $ 28.3 $ 38.1 Liabilities Natural gas related derivatives $ — $ (9.5 ) $ (134.9 ) $ (144.4 ) Total Liabilities $ — $ (9.5 ) $ (134.9 ) $ (144.4 ) At September 30, 2018 Assets Natural gas related derivatives $ — $ 3.9 $ 23.6 $ 27.5 Total Assets $ — $ 3.9 $ 23.6 $ 27.5 Liabilities Natural gas related derivatives $ — $ (5.5 ) $ (117.7 ) $ (123.2 ) Total Liabilities $ — $ (5.5 ) $ (117.7 ) $ (123.2 ) At September 30, 2017 Assets Natural gas related derivatives $ — $ 7.0 $ 17.0 $ 24.0 Total Assets $ — $ 7.0 $ 17.0 $ 24.0 Liabilities Natural gas related derivatives $ — $ (5.7 ) $ (139.6 ) $ (145.3 ) Total Liabilities $ — $ (5.7 ) $ (139.6 ) $ (145.3 )
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	The following tables are a summary of the changes in the fair value of our derivative instruments that are measured at net fair value on a recurring basis in accordance with ASC Topic 820 using significant Level 3 inputs during the three months ended December 31, 2018 , and the fiscal years ended September 30, 2018 and September 30, 2017 , respectively. Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs (In millions) Total - Natural Gas Three Months Ended December 31, 2018 Balance at October 1, 2018 $ (94.1 ) Realized and unrealized gains (losses) Recorded to income (4.4 ) Recorded to regulatory assets—gas costs (5.8 ) Transfers into Level 3 — Transfers out of Level 3 — Settlements (2.3 ) Balance at December 31, 2018 $ (106.6 ) Fiscal Year Ended September 30, 2018 Balance at October 1, 2017 $ (122.6 ) Balance at Realized and unrealized gains (losses) — Recorded to income (4.5 ) Recorded to regulatory assets—gas costs (10.0 ) Transfers into Level 3 (6.9 ) Transfers out of Level 3 8.9 Settlements 41.0 Balance at September 30, 2018 $ (94.1 ) Fiscal Year Ended September 30, 2017 Balance at October 1, 2016 $ (251.6 ) Realized and unrealized gains (losses) Recorded to income 44.2 Recorded to regulatory assets—gas costs 69.7 Transfers into Level 3 (0.4 ) Transfers out of Level 3 (0.4 ) Settlements 15.9 Balance at September 30, 2017 $ (122.6 )
Quantitative Information about Level 3 Fair Value Measurements	The following table includes quantitative information about the significant unobservable inputs used in the fair value measurement of our Level 3 financial instruments and the respective fair values of the net derivative asset and liability positions, by contract type, as of December 31, 2018 , September 30, 2018 and September 30, 2017 . Quantitative Information about Level 3 Fair Value Measurements (In millions) Net Fair Value Valuation Techniques Unobservable Inputs Range Natural gas related derivatives ($106.6) Discounted Cash Flow Natural Gas Basis Price (per dekatherm) ($1.028)-$5.34 Net Fair Value Natural gas related derivatives ($94.1) Discounted Cash Flow Natural Gas Basis Price ($1.003) - $3.886 Net Fair Value Natural gas related derivatives ($122.6) Discounted Cash Flow Natural Gas Basis Price (per dekatherm) ($1.928) - $2.805
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	The table below sets forth the line items on the statements of income to which amounts are recorded for the three months ended December 31, 2018 , and the fiscal years ending September 30, 2018, 2017 and 2016 , respectively, related to fair value measurements using significant Level 3 inputs. Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements (In millions) Total - Natural Gas Fiscal Year Ended December 31, 2018 Utility cost of gas $(4.4) Fiscal Year Ended September 30, 2018 Utility cost of gas $(4.5) Fiscal Year Ended September 30, 2017 Utility cost of gas $44.2 Fiscal Year Ended September 30, 2016 Utility cost of gas $4.0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	Unrealized gains (losses) attributable to derivative assets and liabilities measured using significant Level 3 inputs were recorded as follows for the fiscal years ended December 31, 2018 , and September 30, 2018, 2017 and 2016 , respectively: Unrealized Gains (Losses) Recorded for Level 3 Measurements (In millions) Total - Natural Gas Fiscal Year Ended December 31, 2018 Recorded to income Utility cost of gas $(4.0) Recorded to regulatory assets—gas costs (5.3) Total $(9.3) Fiscal Year Ended September 30, 2018 Recorded to income Utility cost of gas $2.3 Recorded to regulatory assets—gas costs 0.2 Total $2.5 Fiscal Year Ended September 30, 2017 Recorded to income Utility cost of gas $31.0 Recorded to regulatory assets—gas costs 51.0 Total $82.0 Fiscal Year Ended September 30, 2016 Recorded to income Utility cost of gas $0.3 Recorded to regulatory assets—gas costs (2.6) Total $(2.3)
Fair Value of Financial Instruments	The following tables presents the carrying amounts recorded at amortized cost on Washington Gas' balance sheets and estimated fair values of our financial instruments at December 31, 2018 , September 30, 2018 and September 30, 2017 . Washington Gas Light Company Fair Value of Financial Instruments December 31, 2018 September 30, 2018 September 30, 2017 (In millions) Carrying Amount Fair Value Carrying Amount Fair Value Carrying Amount Fair Value Money market funds (a) $ 69.7 $ 69.7 $ 67.3 $ 67.3 $ 4.8 $ 4.8 Commercial paper (b) $ 296.0 $ 296.0 $ 95.0 $ 95.0 $ 123.0 $ 123.0 Project financing (b) $ 15.5 $ 15.5 $ 68.5 $ 68.5 $ 43.8 $ 43.8 Current Maturities of Long-term Debt $ 50.0 $ 50.0 $ 50.0 $ 50.0 $ — $ — Long-term debt (c) $ 1,035.0 $ 1,096.3 $ 1,084.9 $ 1,120.2 $ 1,134.5 $ 1,271.0 (a) The balance as of December 31, 2018 includes $4.4 million money market funds located in "Cash and cash equivalents", $ 20.2 million rabbi trust investment located in "Current Assets-Other", and $ 45.1 million rabbi trust investments located in "Deferred Charges and Other Assets-Other" of the accompanying balance sheets; The balance as of September 30, 2018 includes $2.3 million money market funds located in "Cash and cash equivalents", $ 20.2 million rabbi trust investment located in "Current Assets-Other" and $44.8 million rabbi trust investments located in "Deferred Charges and Other Assets-Other" ; The balance as of September 2017 is located in "Cash and cash equivalents". The amounts in cash and cash equivalent may be offset by outstanding checks. (b) Balance is located in "Notes payable and project financing" in the accompanying balance sheets. (c) Includes adjustments for current maturities and unamortized discounts, as applicable.

Related Party Transactions (Tab

Related Party Transactions (Tables)	3 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Receivables and Payables from Associated Companies	The following table presents the receivables and payables from associated companies as of December 31, 2018, September 30, 2018 and September 30, 2017. Washington Gas Light Company Receivables / Payables from Associated Companies (In millions) December 31, 2018 September 30, 2018 September 30, 2017 Receivables from associated companies (a) $ 4.2 $ 1.1 $ 32.4 Payables to associated companies (a) $ 95.2 $ 16.4 $ 94.8 (a) The receivables and payables do not include the transactions related to shared service cost billed from AltaGas.
Gas Balancing Service Charges	The following table shows the amounts Washington Gas charged WGL Energy Services for balancing services. Washington Gas - Gas Balancing Service Charges Three Month Ended December 31 Fiscal Years Ended September 30, (In millions) 2018 2018 2017 2016 Gas balancing service charge $ 4.6 $ 18.5 $ 23.6 $ 26.8

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The following table shows the changes in accumulated other comprehensive income (loss) for Washington Gas by component for the three months ended December 31, 2018 , and the fiscal years ended September 30, 2018 and September 30, 2017 . Changes in Accumulated Other Comprehensive Income (Loss) by Component Three Months Ended December 31, Fiscal Year Ended September 30, (In thousands) 2018 2018 2017 Beginning Balance $ (1,830 ) $ (4,522 ) $ (7,830 ) Change in prior service cost (a) (226 ) (675 ) (767 ) Amortization of actuarial gain (loss) (a) (6,246 ) 6,324 6,232 Current-period other comprehensive income (loss) (6,472 ) 5,649 5,465 Income tax expense (benefit) related to other comprehensive income (loss) (1,675 ) 2,957 2,157 Ending Balance $ (6,627 ) $ (1,830 ) $ (4,522 ) (a) These accumulated other comprehensive income (loss) components are included in the computation of net periodic benefit cost. Refer to Note 9—Pension and other post-retirement benefit plans for additional details.

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	3 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Information [Abstract]
Supplemental Cash Flow Information Table	The following table details the changes in operating assets and liabilities from operating activities, cash payments that have been included in the determination of earnings and non-cash investing and financing activities: Three Months Ended December 31, Fiscal Year Ended September 30, 2018 2018 2017 2016 (In thousands) CHANGES IN OPERATING ASSETS AND LIABILITIES Accounts receivable and unbilled revenues $ (222,098 ) $ (13,557 ) $ (107,195 ) $ (67,681 ) Receivables from associated companies (1,874 ) 30,135 (18,563 ) (10,623 ) Gas costs and other regulatory assets/liabilities—net 40,028 27,994 3,430 (31,075 ) Storage gas (2,550 ) (8,626 ) (10,280 ) 12,016 Prepaid taxes (9,461 ) 5,618 (6,524 ) 13,539 Accounts payable and other accrued liabilities 61,029 18,378 17,921 34,261 Payables to associated companies 20,662 (73,296 ) 29,074 (2,853 ) Customer deposits and advance payments (29,288 ) 19,464 (16,742 ) (7,514 ) Accrued taxes 1,024 14,619 (4,831 ) 5,980 Other current assets (28 ) (14,605 ) (4,123 ) 3,912 Other current liabilities (121 ) 154 280 (1,318 ) Deferred gas costs—net (51,936 ) (8,306 ) 2,467 (5,104 ) Deferred assets—other 483 (5,895 ) (15,088 ) (22,057 ) Deferred liabilities—other (7,072 ) (21,499 ) (4,667 ) (56,865 ) Pension and other post-retirement benefits (638 ) (14,521 ) (9,806 ) (10,251 ) Other—net — 893 3,409 2,107 Changes in operating assets and liabilities $ (201,840 ) $ (43,050 ) $ (141,238 ) $ (143,526 ) SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION Income taxes paid (refunded)—net $ 3,782 $ (2,983 ) $ — $ (19,004 ) Interest paid $ 4,982 $ 57,036 $ 50,539 $ 40,972 SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING ACTIVITIES: Extinguishment of project debt financing $ (53,018 ) $ (28,312 ) $ (27,927 ) $ — Capital expenditure accruals included in accounts payable and other accrued liabilities $ 33,245 $ 53,367 $ 37,049 $ 43,687
Reconciliation of cash, cash equivalents and restricted cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within Washington Gas’ balance sheets that sums to the total of such amounts shown on the statements of cash flows. (in thousands) December 31, 2018 September 30, 2018 September 30, 2017 September 30, 2016 Cash and cash equivalents $ 6,082 $ 1 $ 1 $ 1 Restricted cash included in Current assets-Other $ 20,207 $ 20,207 $ — $ — Restricted cash included in Deferred Charges and Other Assets-Other $ 45,134 $ 44,775 $ — $ — Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 71,423 $ 64,983 $ 1 $ 1

Merger with AltaGas Ltd. (Table

Merger with AltaGas Ltd. (Tables)	3 Months Ended
	Dec. 31, 2018
Merger with AltaGas Ltd. [Abstract]
Merger related costs	MERGER RELATED COSTS (in millions) Three months ended December 31, 2018 Fiscal year ended September 30, 2018 Merger commitments (a) $ 0.4 $ 139.6 Property plant & equipment impairment (b) — 38.0 Key employee retention payments — 10.5 Acceleration of stock-based compensation (c) — 5.4 Severance costs (d) 2.9 6.7 Total $ 3.3 $ 200.2 (a) See the Merger Commitments table below for details of merger related commitments. (b) Net property, plant and equipment impairment recorded in connection with an agreement not to seek recovery of certain costs incurred under the Formal Case 1027 mechanical coupling program. (c) See Note 10-Stock-Based Compensation for further discussion of the acceleration of incentive compensation. (d) Severance costs are related to the retirement of senior executives following the merger.
Merger commitments	The following table lists total commitments, the amounts paid, and future expected payments as of December 31, 2018. MERGER COMMITMENTS Commitment (Amount in millions) Total Commitment Amount Amount Paid Expected Future Payments Three months ended December 31, 2018 FY 2018 2019 2020 2021 2022 2023 2024-2027 Customer bill credits $ 56.8 $ — $ 56.8 $ — $ — $ — $ — $ — $ — Gas expansion fund contributions 34.2 30.3 — 3.9 — Energy customer or education programs 22.8 — 22.8 — — — — — — Charitable contributions 13.5 0.8 0.4 2.8 1.5 1.5 1.5 1.5 3.5 Work place development initiatives 7.8 — — 3.8 3.8 0.1 0.1 0.1 — Low-income weatherization and energy efficiency initiatives 4.2 — — 2.1 2.1 — — — — Public safety programs 0.7 — — 0.7 — — — — — Total merger commitments $ 140.0 $ 31.1 $ 80.0 $ 13.3 $ 7.4 $ 1.6 $ 1.6 $ 1.6 $ 3.5

Transition Period Comparative_2

Transition Period Comparative Data (Tables)	3 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Transition period comparative data	The following table presents certain financial information for the three months ended December 31, 2018 and 2017. Three Months Ended December 31, $ In thousands 2018 2017 (Unaudited) OPERATING REVENUES $ 402,101 $ 377,470 OPERATING EXPENSES Utility cost of gas 156,641 124,745 Operation and maintenance 102,728 82,372 Depreciation and amortization 34,948 33,646 General taxes and other assessments 38,552 39,983 Total Operating Expenses 332,869 280,746 OPERATING INCOME 69,232 96,724 Other income (expense) — net 3,494 1,029 Interest expense 15,706 14,973 INCOME BEFORE INCOME TAXES 57,020 82,780 INCOME TAX EXPENSE 7,847 24,854 NET INCOME $ 49,173 $ 57,926 Dividends on preferred stock 330 330 NET INCOME APPLICABLE TO COMMON STOCK $ 48,843 $ 57,596

Quarterly Financial Data (Table

Quarterly Financial Data (Tables)	3 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Data	All adjustments necessary for a fair presentation have been included in the quarterly information provided below. Due to the seasonal nature of our business, we report substantial variations in operations on a quarterly basis. Quarter Ended (In thousands) March 31 June 30 September 30 (a) December 31 2018 Operating revenues $ 532,040 $ 199,512 $ 139,041 $ 402,101 Operating income (loss) $ 148,978 $ (6,649 ) $ (225,462 ) 69,232 Net income (loss) $ 108,084 $ (11,499 ) $ (181,153 ) $ 49,173 Net income (loss) applicable to common stock $ 107,754 $ (11,829 ) $ (181,483 ) $ 48,843 2017 Operating revenues $ 475,021 $ 203,186 $ 154,775 $ 377,470 Operating income (loss) $ 164,876 $ 10,482 $ (13,000 ) $ 96,724 Net income (loss) $ 93,610 $ (1,671 ) $ (15,608 ) $ 57,926 Net income (loss) applicable to common stock $ 93,280 $ (2,001 ) $ (15,938 ) $ 57,596 (a) During the quarter ended September 30, 2018, Washington Gas recorded $ 200.2 million of merger related costs due to the Merger with AltaGas.

Accounting Policies (Narrative)

Accounting Policies (Narrative) (Details) $ in Thousands	Jul. 06, 2018	Dec. 31, 2018USD ($)Customers	Sep. 30, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)
Accounting Policies [Table] [Line Items]
Business Acquisition, Effective Date of Acquisition	Jul. 6, 2018
Number of customers (more than one million) | Customers		1,000,000
Pretax AFUDC Rate		5.84%			2.42%	2.73%	5.51%
Composite depreciation and amortization rate		2.78%			2.77%	2.80%	2.69%
Impairment of Oil and Gas Properties			$ 38,000
Regulated revenue billing cycle		19 days
Duration of cost of gas recovered or refunded		12 months
Gross revenue taxes		$ 24,200			$ 82,500	$ 75,100	$ 73,000
Reclass to Other income		3,494		$ 1,029	(7,592)	$ (545)	$ 1,434
ASU 2017-07
Accounting Policies [Table] [Line Items]
Reclass to Other income		$ 11,300		$ 3,600	$ 3,900
Firm Customer
Accounting Policies [Table] [Line Items]
Percentage of total gas deliveries		84.00%
Interruptible Customers
Accounting Policies [Table] [Line Items]
Percentage of total gas deliveries		12.00%
Electric Generation Customers
Accounting Policies [Table] [Line Items]
Percentage of total gas deliveries		4.00%

Accounting Policies Property, P

Accounting Policies Property, Plant and Equipment at Original Cost (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Accounting Policies [Abstract]
Distribution, transmission and storage	$ 4,888.4	$ 4,766.5	$ 4,502.6
General, miscellaneous and intangibles	542.9	536.4	545.6
Construction work in progress (CWIP)	271.6	310.2	262.1
Total	$ 5,702.9	$ 5,613.1	$ 5,310.3
Distribution, transmission and storage, percentage	85.70%	84.90%	84.80%
General, miscellaneous and intangibles percentage	9.50%	9.60%	10.20%
Construction work in progress (CWIP), percentage	4.80%	5.50%	5.00%
Total, percentage	100.00%	100.00%	100.00%

Accounting Policies Changes in

Accounting Policies Changes in Asset Retirement Obligations (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset retirement obligation, current	$ 7.3	$ 7.3	$ 7.1
Changes in Asset Retirement Obligations
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset retirement obligations at beginning of year	305.5	298.9	206.6
Liabilities incurred in the period		1.4	2
Revaluation of asset retirement obligation			89.5
Liabilities settled in the period		(7.3)	(7.2)
Accretion expense	2.6	12.5	8
Asset retirement obligations at the end of the year	$ 308.1	$ 305.5	$ 298.9

Revenue from Contracts With C_4

Revenue from Contracts With Customers - (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		$ 391,500
Other sources of revenue		10,600
Total Operating Revenue		402,101	$ 377,470	$ 1,248,063	$ 1,166,968	$ 1,070,904
Gas and transportation sales | Gas sold and delivered
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		303,200
Gas and transportation sales | Gas delivered for others
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		74,300
Gas and transportation sales | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		12,500
Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		1,500
Revenue from alternative revenue programs
Disaggregation of Revenue [Line Items]
Other sources of revenue	[1]	9,100
Leasing revenue
Disaggregation of Revenue [Line Items]
Other sources of revenue	[2]	200
Other
Disaggregation of Revenue [Line Items]
Other sources of revenue		$ 1,300
[1]	The company has determined that the Utility’s RNA, WNA and CRA billing adjustment mechanisms and accelerated pipe replacement programs are alternative revenue programs and accounted for under ASC Topic 980.
[2]	Revenue generated from Washington Gas lessor operating leases accounted for under ASC Topic 840, Leases.

Regulated Operations (Details)

Regulated Operations (Details) - USD ($) $ in Thousands		3 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Current		$ 6,020	$ 5,054	$ 21,705
Regulatory Assets, Noncurrent		99,105	104,050	104,538
Gas costs due from/to customers
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Current	[1]	5,600	4,400	200
Regulatory Liabilities, Current	[1]	46,900	9,000	10,600
Interruptible Sharing
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Current	[1]	400		2,400
Regulatory Liabilities, Current	[1]	1,700	1,500	700
Revenue normalization mechanisms for Maryland and Virginia
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Current	[1]			11,700
Regulatory Liabilities, Current	[1]	3,600	3,600	1,400
Accelerated replacement recovery mechanisms
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Current	[2]		600	7,400
Regulatory Liabilities, Current	[2]	3,800	1,900	1,100
Rates subject to refund
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities, Current	[3]			9,000
Tax cuts and jobs act
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities, Current	[4]	19,200	18,100
Total current
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Current		6,000	5,000	21,700
Regulatory Liabilities, Current		75,200	34,100	22,800
Accrued Asset Removal Costs
Public Utilities, General Disclosures [Line Items]
Regulatory Liability, Noncurrent	[5]	264,600	270,400	292,200
Deferred Gas Costs
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent	[1],[6]	141,600	83,200	90,100
Deferred pension costs/income-trackers
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent	[7]	5,700	9,100	19,800
Pensions
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent	[1],[8]	80,800	47,900	118,800
Other Post Retirement Benefits
Public Utilities, General Disclosures [Line Items]
Regulatory Liability, Noncurrent	[1],[8]	121,300	159,200	134,200
Total pension and other post-retirement benefits
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent		86,500	57,000	138,600
Regulatory Liability, Noncurrent		121,300	159,200	134,200
Income tax-related amounts due from/to customers
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent	[9]	41,600	42,600	37,900
Regulatory Liability, Noncurrent	[9]	427,200	439,100	3,200
Losses/gains on issuance and extinguishments of debt and interest-rate derivative instruments
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent	[1],[10]	15,000	15,300	16,400
Regulatory Liability, Noncurrent	[1],[10]	1,300	1,300	1,400
Rights-of-way fees
Public Utilities, General Disclosures [Line Items]
Regulatory Liability, Noncurrent	[1]	2,500	1,900	700
Business process outsourcing and related costs
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent	[1]	3,200	6,200	8,200
Non-retirement post-employment benefits
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent	[1],[11]	15,600	16,500	17,800
Deferred distribution integrity management
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent	[1],[12]	5,400	5,800	7,700
Recoverable portion of abandoned liquid natural gas facility(a)
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent		2,700	2,700	3,100
Environmental response costs
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent	[1],[13]	5,800	5,000	2,500
Energy efficiency program-Maryland(n)
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent	[14]	3,400	4,500	5,300
Other regulatory expenses
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent	[15]	6,400	5,500	5,600
Regulatory Liability, Noncurrent	[15]	900	1,400	4,100
Total other
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent		99,100	104,100	104,500
Regulatory Liability, Noncurrent		431,900	443,700	9,400
Total deferred
Public Utilities, General Disclosures [Line Items]
Regulatory Assets, Noncurrent		327,200	244,300	333,200
Regulatory Liability, Noncurrent		817,800	873,300	435,800
Total
Public Utilities, General Disclosures [Line Items]
Regulatory Assets		333,200	249,300	354,900
Regulatory Liabilities		893,000	$ 907,400	$ 458,600
Asset Impairment for Regulatory Action
Public Utilities, General Disclosures [Line Items]
Regulatory Asset, Noncurrent Impairment		$ 2,500
[1]	Washington Gas does not earn its overall rate of return on these assets. Washington Gas is allowed to recover and required to pay, using short-term interest rates, the carrying costs related to billed gas costs due from and to its customers in the District of Columbia and Virginia jurisdictions.
[2]	Balance represents amounts for deferred over or under collections of surcharges associated with Washington Gas' accelerated pipeline recovery programs in the District of Columbia, Maryland and Virginia.
[3]	Represents provision established for refunds to customers when the substitution of final rates resulted in an amount greater than the amount collected during the interim period related to the 2016 Virginia Rate Case.
[4]	Represents amounts accrued for future refunds due to the Tax Cuts and Jobs Act of 2017. For a further discussion, see Rates and Regulatory Matters section of Management's Discussion Analysis and Note 8-Income Taxes in the Notes to Consolidated Financial Statements.
[5]	Refer to Note 1-Accounting Policies for a further discussion of these amounts.
[6]	Includes fair value of derivatives, which are not included in customer bills until settled.
[7]	Relates to the District of Columbia jurisdiction.
[8]	Refer to Note 9-Pension and Other Post-Retirement Benefit Plans for a further discussion of these amounts.
[9]	This balance represents amounts due from customers for deferred tax liabilities related to tax benefits on deduction flowed directly to customers prior to the adoption of income tax normalization for ratemaking purposes and to tax rate changes including the latest reduction as a result of the Tax Act.
[10]	The losses or gains on the issuance and extinguishment of debt and interest-rate derivative instruments include unamortized balances from transactions executed in prior fiscal years. These transactions create gains and losses that are amortized over the remaining life of the debt as prescribed by regulatory accounting requirements.
[11]	Represents the timing difference between the recognition of workers compensation and short-term disability costs in accordance with generally accepted accounting principles and the way these costs are recovered through rates.
[12]	This balance represents amounts for deferred expenditures associated with Washington Gas’ Distribution Integrity Management Program (DIMP) in Virginia.
[13]	This balance represents allowed environmental remediation expenditures at Washington Gas sites to be recovered through rates for Maryland and the District of Columbia. The recovery period is over several years.
[14]	Balance represents amounts for deferred credits associated with Washington Gas' participation in the energy conservation and efficiency program EmPower in Maryland.
[15]	Balance primarily relates to the District of Columbia jurisdiction.

Accounts Payable and Other Ac_3

Accounts Payable and Other Accrued Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Accounts Payable and Accrued Liabilities [Abstract]
Accounts payable—trade	$ 228.9	$ 187	$ 174.9
Employee benefits and payroll accruals	28	32.9	32.4
Other accrued liabilities	31.5	51.4	12.5
Total	$ 288.4	$ 271.3	$ 219.8

Short-Term Debt (Details)

Short-Term Debt (Details) $ in Thousands		Dec. 31, 2018USD ($)	Oct. 01, 2018USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)
Short Term Debt [Line Items]
Less: Commercial Paper		$ (311,460)		$ (163,478)	$ (166,772)
Revolving credit facility additional borrowings		100,000
Revolving credit facility maximum borrowing capacity		$ 450,000
Ratio Of Indebtedness To Net Capital Percentage		47.00%
Payables to associated companies		$ 95,228	$ 53,000	21,548	94,844
Energy management services projects not complete
Short Term Debt [Line Items]
Payables to associated companies		69,700		8,500	41,800
Notes payable and project financing		15,500		68,500	43,800
Unbilled revenues		85,300		77,000	85,600
Reserve for bad debt		0		0	0
Committed credit
Short Term Debt [Line Items]
Unsecured revolving credit facility	[1]	350,000		350,000	350,000
Less: Commercial Paper		(296,000)		(95,000)	(123,000)
Net committed credit available		$ 54,000		$ 255,000	$ 227,000
Weighted average interest rate		2.93%		2.42%	1.22%
Outstanding bank loans		$ 0		$ 0	$ 0
Maximum
Short Term Debt [Line Items]
Ratio of Indebtedness to Net Capital		1
Ratio Of Indebtedness To Net Capital Percentage		65.00%
Minimum
Short Term Debt [Line Items]
Ratio of Indebtedness to Net Capital		0.65
[1]	Washington Gas has the right to request extensions with the banks’ approval. Washington Gas’ revolving credit facility permits it to borrow an additional $100 million, with the banks’ approval, for a total of $450 million.

Long Term Debt (Details)

Long Term Debt (Details) - USD ($)		3 Months Ended	12 Months Ended
		Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2018
Long Term Debt [LIne Items]
Long term debt outstanding	[1]	$ 1,096,000,000	$ 1,146,000,000	$ 1,146,000,000
Unamortized discount		(2,900,000)	(3,000,000)	(2,900,000)
Unamortized Debt Issuance Expense		(8,100,000)	(8,500,000)	(8,100,000)
Less-current maturities		50,000,000	0	50,000,000
Total Long-Term Debt		$ 1,035,000,000	$ 1,134,500,000	$ 1,085,000,000
Weighted Average Interest Rate	[2]	4.77%	4.89%	4.89%
Mortgage
Long Term Debt [LIne Items]
Mortgage Debt Outstanding		$ 0	$ 0	$ 0
Medium-term Notes
Long Term Debt [LIne Items]
Additional borrowing capacity		725,000,000
Maturities
Long Term Debt [LIne Items]
Principle amount of debt due in 2019		50,000,000
Principle amount of debt due in 2023		20,000,000
Principle amount of debt due after five years		1,026,000,000
Maturities 2046 Notes | Issuances
Long Term Debt [LIne Items]
Principal	[3]		$ 200,000,000
Interest Rate	[4]		3.80%
Nominal Maturity Date			Sep. 15, 2046
Maturities 2046 Notes | Total
Long Term Debt [LIne Items]
Principal	[3]		$ 200,000,000
Maturities 2018 Notes | Retirements
Long Term Debt [LIne Items]
Principal	[3]	$ 50,000,000
Interest Rate	[4]	7.46%
Effective Cost	[4]	7.46%
Nominal Maturity Date		Dec. 5, 2018
Maturities 2018 Notes | Total
Long Term Debt [LIne Items]
Principal	[3]	$ 50,000,000
Due in 2019
Long Term Debt [LIne Items]
Long term debt outstanding		$ 50,000,000	$ 50,000,000	$ 50,000,000
Note rate		4.76%	7.46%	7.46%
Due in 2020
Long Term Debt [LIne Items]
Long term debt outstanding			$ 50,000,000	$ 50,000,000
Note rate			4.76%	4.76%
Due in 2023
Long Term Debt [LIne Items]
Long term debt outstanding		$ 20,000,000	$ 20,000,000	$ 20,000,000
Note rate		6.65%	6.65%	6.65%
Due in 2025
Long Term Debt [LIne Items]
Long term debt outstanding		$ 40,500,000	$ 40,500,000	$ 40,500,000
Note rate		5.44%	5.44%	5.44%
Due in 2026
Long Term Debt [LIne Items]
Long term debt outstanding		$ 53,000,000
Due in 2027
Long Term Debt [LIne Items]
Long term debt outstanding		72,000,000	$ 125,000,000	$ 125,000,000
Due in 2028
Long Term Debt [LIne Items]
Long term debt outstanding		52,000,000	52,000,000	52,000,000
Due in 2030
Long Term Debt [LIne Items]
Long term debt outstanding		$ 8,500,000	$ 8,500,000	$ 8,500,000
Note rate		7.50%	7.50%	7.50%
Due in 2036
Long Term Debt [LIne Items]
Long term debt outstanding		$ 50,000,000	$ 50,000,000	$ 50,000,000
Due in 2040
Long Term Debt [LIne Items]
Long term debt outstanding		$ 75,000,000
Note rate		5.21%
Due in 2041
Long Term Debt [LIne Items]
Long term debt outstanding			$ 75,000,000	$ 75,000,000
Note rate			5.21%	5.21%
Due in 2043
Long Term Debt [LIne Items]
Long term debt outstanding		$ 75,000,000
Note rate		5.00%
Due in 2044
Long Term Debt [LIne Items]
Long term debt outstanding		$ 150,000,000	$ 175,000,000	$ 175,000,000
Due in 2045
Long Term Debt [LIne Items]
Long term debt outstanding			$ 50,000,000	$ 50,000,000
Note rate			4.24%	4.24%
Due in 2046
Long Term Debt [LIne Items]
Long term debt outstanding		$ 450,000,000	$ 450,000,000	$ 450,000,000
Note rate		3.80%	3.80%	3.80%
Maximum | Due in 2026
Long Term Debt [LIne Items]
Note rate		6.82%
Maximum | Due in 2027
Long Term Debt [LIne Items]
Note rate		6.57%	6.82%	6.82%
Maximum | Due in 2028
Long Term Debt [LIne Items]
Note rate		6.85%	6.85%	6.85%
Maximum | Due in 2036
Long Term Debt [LIne Items]
Note rate		5.78%	5.78%	5.78%
Maximum | Due in 2044
Long Term Debt [LIne Items]
Note rate		4.24%	5.00%	5.00%
Minimum | Due in 2026
Long Term Debt [LIne Items]
Note rate		6.62%
Minimum | Due in 2027
Long Term Debt [LIne Items]
Note rate		6.40%	6.40%	6.40%
Minimum | Due in 2028
Long Term Debt [LIne Items]
Note rate		6.57%	6.57%	6.57%
Minimum | Due in 2036
Long Term Debt [LIne Items]
Note rate		5.70%	5.70%	5.70%
Minimum | Due in 2044
Long Term Debt [LIne Items]
Note rate		4.22%	4.22%	4.22%
[1]	Includes MTNs and private placement notes. The amount represents face value of long-term debt including current maturities.
[2]	Weighted average interest rate is for the long-term debt including current maturities.
[3]	Represents face amount of notes.
[4]	Represents the interest rate and effective cost at the trade date of the debt.

Preferred Stock (Details)

Preferred Stock (Details)	Dec. 31, 2018$ / sharesshares
Series One
Preferred Stock, Par or Stated Value Per Share (in dollars per share)	$ 4.80
Preferred Stock, Shares Outstanding (in shares) | shares	150,000
Preferred Stock, Liquidation Preference Per Share Involuntary (in dollars per share)	$ 100
Preferred Stock Liquidation Preference Voluntary (in dollars per share)	101
Preferred Stock, Redemption Price Per Share (in dollars per share)	101
Series Two
Preferred Stock, Par or Stated Value Per Share (in dollars per share)	$ 4.25
Preferred Stock, Shares Outstanding (in shares) | shares	70,600
Preferred Stock, Liquidation Preference Per Share Involuntary (in dollars per share)	$ 100
Preferred Stock Liquidation Preference Voluntary (in dollars per share)	105
Preferred Stock, Redemption Price Per Share (in dollars per share)	105
Series Three
Preferred Stock, Par or Stated Value Per Share (in dollars per share)	$ 5
Preferred Stock, Shares Outstanding (in shares) | shares	60,000
Preferred Stock, Liquidation Preference Per Share Involuntary (in dollars per share)	$ 100
Preferred Stock Liquidation Preference Voluntary (in dollars per share)	102
Preferred Stock, Redemption Price Per Share (in dollars per share)	$ 102

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Thousands		Jan. 01, 2018	Dec. 22, 2017	Dec. 31, 2018		Dec. 31, 2017	Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2016
Income Taxes [Line Items]
Total deferred				$ 8,012	[1]		$ (26,435)	[1]	$ 77,586	$ 123,482
Tax sharing - amount paid to subsidiaries with taxable income				$ 8,300
Tax sharing - amount received from subsidiaries with taxable income							$ 2,900
Federal corporate income tax rate	[2]			21.00%			21.00%		35.00%	35.00%
Unrecognized tax benefits increase (decrease)				$ 7,700			$ 4,400
Reduction in regulated revenue				(402,101)		$ (377,470)	(1,248,063)		$ (1,166,968)	$ (1,070,904)
Deferred tax liabilities decrease				454,248			409,807		888,385
Regulatory liability increase (decrease)				431,913			443,665		9,403
Income tax expense (benefit)				7,847		$ 24,854	(25,863)		79,840	71,666
Accrued interest expense or penalties				0			0		$ 0	$ 0
Tax cuts and jobs act
Income Taxes [Line Items]
Federal corporate income tax rate		21.00%	35.00%
Bonus depreciation							86,200
Bonus depreciation eligible assets				17,400
Reduction in regulated revenue		$ (41,200)		(13,700)			(27,500)
Uncertain tax position
Income Taxes [Line Items]
Deferred tax liabilities decrease				0			14,800
Re measurement of deferred income taxes
Income Taxes [Line Items]
Regulatory liability increase (decrease)				(6,100)
Income tax expense (benefit)				1,200			7,000
Re measurement of deferred income taxes | Excess Deferred Income Taxes
Income Taxes [Line Items]
Regulatory liability increase (decrease)							431,000
Re measurement of deferred income taxes | Re measurement of excess deferred taxes and net operating lass carryforward deferred tax asset
Income Taxes [Line Items]
Regulatory liability increase (decrease)				5,900
Income tax expense (benefit)				$ 1,200
Re measurement of deferred income taxes | Deferred tax assets not associated with rate-making
Income Taxes [Line Items]
Income tax expense (benefit)							7,000
Re measurement of deferred income taxes | Plant related
Income Taxes [Line Items]
Deferred tax liabilities decrease							$ 421,700
[1]	Includes tax expense of $1.2 million and $7.0 million related to re-measurement of deferred income taxes for the three months ended December 31, 2018 and the fiscal year ended September 30, 2018, respectively.
[2]	As a result of the merger with AltaGas, Washington Gas is subject to two separate short periods and accompanying returns. The first period through July 6, 2018 is subjected to a higher, blended federal statutory rate. Due to the net operating loss for federal tax purposes through September 30, 2018, all the year activity is ultimately taxed at 21%. As such, for presentational purposes, we applied a 21% rate to the entire fiscal year 2018 activity.

Income Taxes (Components of Inc

Income Taxes (Components of Income Tax Expense) (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017	Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2016
Current
Federal						$ 1,722	$ (48,064)
State				$ 1,274		1,283	(2,957)
Total current				1,274		3,005	(51,021)
Deferred
Total deferred	$ 8,012	[1]		(26,435)	[1]	77,586	123,482
Income tax expense (benefit)	7,847		$ 24,854	(25,863)		79,840	71,666
Accelerated Depreciation [Member]
Deferred
Federal	6,494			(27,846)		83,009	93,385
State	2,416			12,533		15,033	13,081
Other Federal
Deferred
Federal	2,537			(8,485)		(18,419)	13,826
Other State
Deferred
State	(3,435)			(2,637)		(2,037)	3,190
Amortization of investment tax credits
Deferred
Amortization of investment tax credits	(165)			(702)		$ (751)	$ (795)
Re measurement of deferred income taxes
Deferred
Income tax expense (benefit)	$ 1,200			$ 7,000
[1]	Includes tax expense of $1.2 million and $7.0 million related to re-measurement of deferred income taxes for the three months ended December 31, 2018 and the fiscal year ended September 30, 2018, respectively.

Income Taxes (Tax Rate Reconcil

Income Taxes (Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income taxes at statutory federal tax rate	[1]	$ 11,974		$ (11,026)	$ 74,071	$ 64,673
Statutory federal income tax rate (%)	[1]	21.00%		21.00%	35.00%	35.00%
Plant basis difference		$ (4,261)		$ 1,079	$ 2,213	$ 2,445
Plant basis difference (%)		(7.47%)		(2.06%)	1.05%	1.32%
Allowance for funds used during construction		$ (520)		$ (70)	$ (291)	$ (509)
Allowance for funds used during construction (%)		(0.91%)		0.13%	(0.14%)	(0.28%)
Amortization of investment tax credits		$ (165)		$ (703)	$ (751)	$ (795)
Amortization of investment tax credits (%)		(0.29%)		1.34%	(0.35%)	(0.43%)
Amortization of excess deferred taxes		$ (2,431)		$ (9,798)	$ (196)
Amortization of excess deferred taxes (%)		(4.26%)		(18.66%)	(0.09%)
Cost of removal		$ (28)		$ (1,561)	$ (2,944)	$ (3,722)
Cost of removal (%)		(0.05%)		2.97%	(1.39%)	(2.01%)
State income taxes-net of federal benefit		$ 2,737		$ (2,659)	$ 9,482	$ 8,310
State income taxes-net of federal benefit (%)		4.80%		5.06%	4.48%	4.50%
Consolidated tax sharing allocation						$ 1,073
Consolidated tax sharing allocation (%)						0.58%
Re-measurement		$ 1,243		$ 7,031
Re-measurement (%)		2.18%		(13.39%)
ASU 2016-09 adoption				$ (3,223)
ASU 2016-09 adoption (%)				6.14%
Book to provision adjustment				$ (4,669)	$ (4,859)	$ (1,353)
Book to provision adjustment (%)				8.89%	(2.30%)	(0.73%)
Other items-net		$ (702)		$ (264)	$ 3,115	$ 1,544
Other items-net (%)		(1.23%)		0.50%	1.47%	0.84%
Income tax expense (benefit)		$ 7,847	$ 24,854	$ (25,863)	$ 79,840	$ 71,666
Total income tax expense (benefit) and effective tax rate (%)		13.77%		49.24%	37.73%	38.79%
[1]	As a result of the merger with AltaGas, Washington Gas is subject to two separate short periods and accompanying returns. The first period through July 6, 2018 is subjected to a higher, blended federal statutory rate. Due to the net operating loss for federal tax purposes through September 30, 2018, all the year activity is ultimately taxed at 21%. As such, for presentational purposes, we applied a 21% rate to the entire fiscal year 2018 activity.

Income Taxes (Components of Acc

Income Taxes (Components of Accumulated Deferred Tax Assets (Liabilities)) (Details) - Non-current - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Deferred Income Tax Assets:
Pensions	$ 25,629	$ 43,071	$ 41,907
Uncollectible accounts	1,680	1,131	7,815
Inventory overheads	4,088	4,090	6,617
Employee compensation and benefits	40,960	51,006	47,479
Income taxes recoverable through future rates	96,256	121,357	33,324
Derivatives	8,737	7,435	11,187
Deferred gas costs			1,485
Net operating loss	84,674	90,943
Total assets	262,024	319,033	116,490
Deferred Income Tax Liabilities:
Other post-retirement benefits	63,540	106,289	89,494
Accelerated depreciation and other plant related items	636,196	615,499	876,235
Losses/gains on reacquired debt	571	581	1,047
Income taxes recoverable through future rates	96,256	121,357	33,324
Deferred gas costs	14,928	3,041
Other	1,037	3,430	4,775
Total liabilities	716,272	728,840	1,004,875
Net accumulated deferred income tax assets (liabilities)	$ (454,248)	$ (409,807)	$ (888,385)

Income Taxes (Unrecognized Tax

Income Taxes (Unrecognized Tax Benefits) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Unrecognized Tax Benefits
Total unrecognized tax benefits, beginning balance	$ 43,567	$ 48,009	$ 42,283	$ 38,627
Increases in tax positions relating to current period	2,574	10,947	10,766	10,645
Decreases in tax positions relating to prior periods	(10,235)	(15,389)	(5,040)	(6,989)
Total unrecognized tax benefits, ending balance	$ 35,906	$ 43,567	$ 48,009	$ 42,283

Pension and Other Post-retire_3

Pension and Other Post-retirement Benefit Plans (Narrative) (Details) - USD ($)	Jan. 01, 2018	Sep. 30, 2015	Dec. 31, 2018		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2016	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Percentage Of Prior Years Asset Gains And Losses Recognized					20.00%
Total matching contributions			$ 1,100,000		$ 5,000,000		$ 4,600,000		$ 4,400,000
Total supplemental contributions			700,000		2,700,000		2,200,000		1,900,000
Prior service credit related to plan amendment		$ 26,100,000	226,000	[1]	$ 675,000	[1]	767,000	[1]	891,000
Realized and unrealized gains and losses on equities prior year					80.00%
Realized and unrealized gains and losses on equities second prior year					60.00%
Realized and unrealized gains and losses on equities third prior year					40.00%
Realized and unrealized gains and losses on equities fourth prior year					20.00%
Reclassified amount of Net Periodic Benefit Income due to adoption of ASU 2017-07					$ 11,300,000		3,900,000		3,600,000
Restricted cash included in Current assets-Other			20,347,000		20,347,000		102,000
Restricted cash included in Deferred Charges and Other Assets-Other			$ 50,490,000		$ 49,331,000		3,561,000
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Mortality assumptions			The RP-2014 mortality table and MP-2018 improvement scale were used to determine the benefit obligation as of December 31, 2018. The benefit obligations as of September 30, 2018 and 2017 were determined using the RP-2014 mortality tables and a modified improvement scale. We modified the MP-2014 improvement scale to (a) adjust the ultimate long-term rate of mortality improvement from 1.00% to 0.75% per annum up to age 85 trending down to 0% between age 85 and age 115; and (b) shorten the convergence period from short term to ultimate rates of improvement from the 20-year period to a 15-year period.
HRA Stipend Increase					0.00%
Defined Benefit Plan Target Allocation Percentage [Abstract]
Asset Class Allocations Allowed Range Within Plus Or Minus					5.00%
Rabbi Trusts
Defined Benefit Plan Disclosure [Line Items]
Restricted cash included in Deferred Charges and Other Assets-Other					$ 40,600,000
Scenario, Forecast
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
HRA Stipend Increase										3.00%	0.00%
Scenario, Forecast | Fiscal year 2019
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Future Healthcare Cost Trend Rates											6.50%
Scenario, Forecast | Fiscal year 2020
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Future Healthcare Cost Trend Rates										2.10%
Union Eligible Employee
Defined Benefit Plan Target Allocation Percentage [Abstract]
US Large Cap Equities					40.00%
Fixed Income And Cash					60.00%
Management Employee
Defined Benefit Plan Target Allocation Percentage [Abstract]
US Large Cap Equities					50.00%
Fixed Income And Cash					50.00%
Aggregate Cost Limit Per Individual
Defined Benefit Plan Disclosure [Line Items]
Retiree Medical employer sponsored coverage limits under amendment	$ 11,850
Aggregate Cost Limit Per Family
Defined Benefit Plan Disclosure [Line Items]
Retiree Medical employer sponsored coverage limits under amendment	$ 30,950
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service credit related to plan amendment			$ 100,000		$ 300,000		300,000		300,000
Reclassified amount of Net Periodic Benefit Income due to adoption of ASU 2017-07			4,200,000		28,100,000		36,200,000		31,800,000
The projected benefit obligation (PBO)			906,200,000		$ 923,600,000		983,100,000
Defined Benefit Plan Target Allocation Percentage [Abstract]
US Large Cap Equities					32.00%
International Equities					8.00%
Real Estate Investments					5.00%
Fixed Income And Cash					55.00%
Employer payment current fiscal year					$ 0
Pension Plan | Scenario, Forecast
Defined Benefit Plan Target Allocation Percentage [Abstract]
Estimated future employer contributions in next fiscal year											$ 0
Other post-retirement benefits
Defined Benefit Plan Disclosure [Line Items]
Prior service credit related to plan amendment			(4,400,000)		(17,600,000)		(17,700,000)		(17,700,000)
Reclassified amount of Net Periodic Benefit Income due to adoption of ASU 2017-07			(6,200,000)		(24,300,000)		(20,400,000)		$ (19,200,000)
Defined Benefit Plan Target Allocation Percentage [Abstract]
Employer payment current fiscal year					1,300,000
DB Restoration
Defined Benefit Plan Disclosure [Line Items]
The projected benefit obligation (PBO)			4,100,000		4,000,000		4,200,000
DB Restoration | Rabbi Trusts
Defined Benefit Plan Disclosure [Line Items]
Restricted cash included in Current assets-Other					20,200,000
DB SERP
Defined Benefit Plan Disclosure [Line Items]
Actuarial net loss			4,100,000
The projected benefit obligation (PBO)			61,500,000		62,200,000		$ 60,200,000
Amount reclassified to AOCI due to regulatory action			$ 2,900,000
Defined Benefit Plan Target Allocation Percentage [Abstract]
Employer payment current fiscal year					500,000
Estimated future employer contributions in next fiscal year					20,200,000
DB SERP | Rabbi Trusts
Defined Benefit Plan Disclosure [Line Items]
Restricted cash included in Current assets-Other					$ 60,800,000
Maximum
Defined Benefit Plan Disclosure [Line Items]
Percentage Of supplemental contribution					6.00%
Minimum
Defined Benefit Plan Disclosure [Line Items]
Percentage Of supplemental contribution					4.00%
[1]	These accumulated other comprehensive income (loss) components are included in the computation of net periodic benefit cost. Refer to Note 9—Pension and other post-retirement benefit plans for additional details.

Pension and Other Post-retire_4

Pension and Other Post-retirement Benefit Plans (Post-Retirement Benefits Table) (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Dec. 31, 2018		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2016
Total Recognized
Non-current asset		$ 249,462		$ 284,277		$ 230,283
Non-current liability		(156,210)		(118,204)		(179,814)
Pension Plan
Change in projected benefit obligation
Benefit obligation at beginning of year	[1]	989,800		1,047,500		1,069,300
Service cost		3,000	[1]	14,900	[1]	16,500	[1]	$ 14,200
Interest cost		10,600	[1]	39,600	[1]	38,400	[1]	41,300
Change in plan benefits	[1]	200
Actuarial loss (gain)	[1]	(17,300)		(65,200)		(28,200)
Projected benefit obligation at end of year	[1]	971,800		989,800		1,047,500		1,069,300
Change in plan assets
Fair Value of plan assets at beginning of year	[1]	863,900	[2]	872,500		850,000
Actual return on plan assets	[1]	(42,300)		38,800		68,600
Company contributions	[1]	400		1,800		4,400
Expenses	[1]	(500)		(2,200)		(2,000)
Benefits Paid	[1]	(14,500)		(47,000)		(48,500)
Fair value of plan assets at end of year	[1]	807,000	[2]	863,900	[2]	872,500		850,000
Funded status at end of year	[1]	(164,800)		(125,900)		(175,000)
Allocation to affiliates		(1,600)		(1,300)		(1,700)
Adjusted funded status at end of period		(163,200)		(124,600)		(173,300)
Total Recognized
Current liability	[1]	(20,200)		(20,200)		(6,500)
Non-current liability	[1]	(143,000)		(104,400)		(166,800)
Total Recognized	[1]	(163,200)		(124,600)		(173,300)
Other post-retirement benefits
Change in projected benefit obligation
Benefit obligation at beginning of year		283,300	[3]	309,000	[3]	324,300
Service cost		1,300		5,300		5,800		4,600
Interest cost		3,000		11,700		11,700		13,100
Change in plan benefits						1,100
Actuarial loss (gain)		(6,200)		(28,700)		(18,900)
Retiree contributions		900		1,900		1,800
Projected benefit obligation at end of year		277,900	[3]	283,300	[3]	309,000	[3]	324,300
Change in plan assets
Fair Value of plan assets at beginning of year		569,300		540,500		505,000
Actual return on plan assets		(32,000)		43,000		48,100
Company contributions		1,300		5,000		8,200
Retiree Contributions and employer group waiver plan rebates		900		1,900		1,800
Expenses		(6,300)		(5,200)		(5,800)
Benefits Paid		(4,400)		(15,900)		(16,800)
Fair value of plan assets at end of year		528,800		569,300		540,500		$ 505,000
Funded status at end of year		250,900		286,000		231,500
Allocation to affiliates		1,400		1,700		1,200
Adjusted funded status at end of period		249,500		284,300		230,300
Total Recognized
Total Recognized		$ 249,500		$ 284,300		$ 230,300
[1]	The DB SERP and DB Restoration, included in pension benefits in the table above, does not include the amounts funded in rabbi trust.
[2]	This table does not include rabbi trust investments located in "Current Assets-Other" and "Deferred Charges and Other Assets-Other" on our balance sheets. Refer to
[3]	For the Health and Life Benefits, the change in projected benefit obligation represents the accumulated benefit obligation.

Pension and Other Post-retire_5

Pension and Other Post-retirement Benefit Plans (Projected and ABO) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 906.2	$ 923.6	$ 983.1
Accumulated benefit obligation	847.1	859.1	905.8
DB SERP
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	61.5	62.2	60.2
Accumulated benefit obligation	59.8	60.7	57.5
DB Restoration
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	4.1	4	4.2
Accumulated benefit obligation	$ 3.2	$ 3	$ 3

Pension and Other Post-retire_6

Pension and Other Post-retirement Benefit Plans (Unrecognized Costs Income Recorded on BS) (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Dec. 31, 2018		Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2016
Unrecognized Costs/Income Recorded on the Balance Sheet
Deferred Income Tax Expense (Benefit)		$ 8,012	[1]	$ (26,435)	[1]	$ 77,586	$ 123,482
AOCI, tax expense (benefit)		2,400		700		3,600
Pension Plan
Unrecognized Costs/Income Recorded on the Balance Sheet
Unrecognized actuarial net loss		96,100		61,000		136,100
Unrecognized prior service cost (credit)		1,000		900		1,200
Total	[2]	97,100		61,900		137,300
Regulatory asset	[2]	80,800		47,900		118,800
Pre-tax accumulated other comprehensive loss (gain)	[3]	15,900		13,700		17,700
Total		96,700		61,600		136,500
Unrecognized pension and health and life benefits allocated to affiliates		400		300		800
Deferred Income Tax Expense (Benefit)				200		2,200
Other post-retirement benefits
Unrecognized Costs/Income Recorded on the Balance Sheet
Unrecognized actuarial net loss		(26,000)		(64,500)		(21,800)
Unrecognized prior service cost (credit)		(102,800)		(107,200)		(124,900)
Total	[2]	(128,800)		(171,700)		(146,700)
Regulatory asset	[2]	(121,100)		(159,400)		(136,400)
Pre-tax accumulated other comprehensive loss (gain)	[3]	(6,900)		(11,200)		(9,500)
Total		(128,000)		(170,600)		(145,900)
Unrecognized pension and health and life benefits allocated to affiliates		$ 800		$ 1,100		$ 800
[1]	Includes tax expense of $1.2 million and $7.0 million related to re-measurement of deferred income taxes for the three months ended December 31, 2018 and the fiscal year ended September 30, 2018, respectively.
[2]	The regulatory liability recorded on our balance sheet at September 30, 2018 and September 30, 2017 is net of a deferred income tax benefit of $0.2 million and $2.2 million, respectively.
[3]	The total amount of accumulated other comprehensive loss recorded on our balance sheets at December 31, 2018, September 30, 2018 and September 30, 2017 is net of an income tax benefit of $2.4 million, $0.7 million and $3.6 million, respectively.

Pension and Other Post-retire_7

Pension and Other Post-retirement Benefit Plans (Recognized in Curent Period and Next Year) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2019
Pension Plan | Regulatory Assets and Liabilities
Amounts Recognized During Current Period
Actuarial net loss	$ 1
Prior service cost (credit)	0.1
Total	1.1
Pension Plan | Regulatory Assets and Liabilities | Expected to be recognized
Amounts to be Recognized During Next Year
Actuarial net loss		$ 3.4
Prior service cost (credit)		0.1
Total		3.5
Pension Plan | Accumulated Other Comprehensive Loss
Amounts Recognized During Current Period
Actuarial net loss	0.4
Prior service cost (credit)	0
Total	0.4
Pension Plan | Accumulated Other Comprehensive Loss | Expected to be recognized
Amounts to be Recognized During Next Year
Actuarial net loss		1.7
Prior service cost (credit)		0.2
Total		1.9
Health and Life Benefits | Regulatory Assets and Liabilities
Amounts Recognized During Current Period
Actuarial net loss	0
Prior service cost (credit)	(4.1)
Total	(4.1)
Health and Life Benefits | Regulatory Assets and Liabilities | Expected to be recognized
Amounts to be Recognized During Next Year
Actuarial net loss		0
Prior service cost (credit)		(15)
Total		(15)
Health and Life Benefits | Accumulated Other Comprehensive Loss
Amounts Recognized During Current Period
Actuarial net loss	0
Prior service cost (credit)	(0.3)
Total	$ (0.3)
Health and Life Benefits | Accumulated Other Comprehensive Loss | Expected to be recognized
Amounts to be Recognized During Next Year
Actuarial net loss		0
Prior service cost (credit)		(0.8)
Total		$ (0.8)

Pension and Other Post-retire_8

Pension and Other Post-retirement Benefit Plans (Components of Net Periodic Benefit Cost Income) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2018		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Recognized prior service cost (credit)	$ 26,100	$ 226	[1]	$ 675	[1]	$ 767	[1]	$ 891
Recognized actuarial loss		6,246	[1]	(6,324)	[1]	(6,232)	[1]	936
Net periodic benefit cost				11,300		3,900		3,600
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost		3,000	[2]	14,900	[2]	16,500	[2]	14,200
Interest cost		10,600	[2]	39,600	[2]	38,400	[2]	41,300
Expected return on plan assets		(10,900)		(42,300)		(41,000)		(40,900)
Recognized prior service cost (credit)		100		300		300		300
Recognized actuarial loss		1,400		15,600		22,000		16,900
Net periodic benefit cost		4,200		28,100		36,200		31,800
Allocation to affiliates		(400)		(4,200)		(2,900)		(1,900)
Adjusted net periodic benefit cost		(3,800)		(23,900)		(33,300)		(29,900)
Amount allocated to construction projects		(600)		(4,700)		(6,400)		(5,600)
Amount deferred as regulatory asset (liability)-net		1,500		5,900		6,900		7,100
Amount charged (credited) to expense		4,700		25,100		33,800		31,400
Health and Life Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		1,300		5,300		5,800		4,600
Interest cost		3,000		11,700		11,700		13,100
Expected return on plan assets		(6,100)		(23,700)		(22,100)		(20,400)
Recognized prior service cost (credit)		(4,400)		(17,600)		(17,700)		(17,700)
Recognized actuarial loss						1,900		1,200
Net periodic benefit cost		(6,200)		(24,300)		(20,400)		(19,200)
Allocation to affiliates		800		3,100		1,400		1,100
Adjusted net periodic benefit cost		(5,400)		(21,200)		(19,000)		(18,100)
Amount allocated to construction projects		(200)		4,000		4,600		4,100
Amount deferred as regulatory asset (liability)-net								(200)
Amount charged (credited) to expense		$ (5,600)		$ (17,200)		$ (14,400)		$ (14,200)
[1]	These accumulated other comprehensive income (loss) components are included in the computation of net periodic benefit cost. Refer to Note 9—Pension and other post-retirement benefit plans for additional details.
[2]	The DB SERP and DB Restoration, included in pension benefits in the table above, does not include the amounts funded in rabbi trust.

Pension and Other Post-retire_9

Pension and Other Post-retirement Benefit Plans (Benefit Obligations and Net Periodic Benefit Cost Assumptions) (Details)		3 Months Ended	12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Pension Plan
Net Periodic Benefit Cost Assumptions [Abstract]
Expected long-term return on plan assets	[1]	5.75%	5.75%	5.75%	6.00%
Pension Plan | Maximum
Benefit Obligations Assumptions [Abstract]
Discount rate	[2]	4.40%	4.40%	3.90%	3.70%
Rate of compensation increase		4.10%	4.10%	4.10%	4.10%
Net Periodic Benefit Cost Assumptions [Abstract]
Discount rate	[3]	4.40%	3.90%	3.70%	4.50%
Rate of compensation increase	[4]	4.10%	4.10%	4.10%	4.10%
Pension Plan | Minimum
Benefit Obligations Assumptions [Abstract]
Discount rate	[2]	4.30%	4.30%	3.60%	3.40%
Rate of compensation increase		3.50%	3.50%	3.50%	3.50%
Net Periodic Benefit Cost Assumptions [Abstract]
Discount rate	[3]	4.30%	3.60%	3.40%	4.10%
Rate of compensation increase	[4]	3.50%	3.50%	3.50%	3.50%
Health and Life Benefits
Benefit Obligations Assumptions [Abstract]
Discount rate	[2]	4.40%	4.40%	3.90%	3.70%
Rate of compensation increase		4.10%	4.10%	4.10%	4.10%
Net Periodic Benefit Cost Assumptions [Abstract]
Discount rate	[3]	4.40%	3.90%	3.70%	4.50%
Expected long-term return on plan assets	[1]	5.25%	5.50%	5.50%	5.75%
Rate of compensation increase	[4]	4.10%	4.10%	4.10%	4.10%
Assumed Income Tax Rate		42.20%
[1]	For health and life benefits, the expected returns for certain funds may be lower due to certain portions of income that are subject to an assumed income tax rate of 42.2%.
[2]	The increase in the discount rate in the three months ended December 31, 2018 and fiscal year 2018 compared to prior years primarily reflects the increase in long-term interest rates.
[3]	The changes in the discount rates over the last three fiscal years primarily reflect the changes in long-term interest rates.
[4]	The changes in the rate of compensation reflects the best estimates of actual future compensation levels including consideration of general price levels, productivity, seniority, promotion, and other factors such as inflation rates.

Pension and Other Post-retir_10

Pension and Other Post-retirement Benefit Plans (Healthcare Trends) (Details) $ in Millions	12 Months Ended
	Sep. 30, 2018USD ($)
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Increase one percentage point total service and interest cost components	$ 0.2
Decrease one percentage point total service and interest cost components	(0.1)
Increase one percentage point post-retirement benefit obligation	5.2
Decrease one percentage point post-retirement benefit obligation	$ (4.6)

Pension and Other Post-retir_11

Pension and Other Post-retirement Benefit Plans (Plan Assets) (Details) - USD ($) $ in Millions		Dec. 31, 2018		Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2016
Pension Plan
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 483.3		$ 492.6		$ 513.2
Total fair value of plan investments		808.2		861		875.2
Receivable (Payable)	[1]	(1.2)		2.9		(2.7)
Fair value of plan assets at end of year	[2]	$ 807	[3]	$ 863.9	[3]	$ 872.5	$ 850
Percentage of fair value of plan investments		59.80%		57.20%		58.80%
Total fair value of plan assets (%)		100.10%		99.70%		100.30%
Percent Receivable (Payable)	[1]	(0.10%)		0.30%		(0.30%)
Total plan assets percent		100.00%	[3]	100.00%	[3]	100.00%
Pension Plan | Level 1
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 37.1		$ 44.6		$ 42.1
Pension Plan | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		446.2		448		471.1
Pension Plan | Level 3
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		0		0		0
Pension Plan | Cash and Cash Equivalents
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 0.7		$ 2.2		$ 0.7
Percentage of fair value of plan investments		0.10%		0.30%		0.10%
Pension Plan | Cash and Cash Equivalents | Level 1
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 0.7		$ 2.2		$ 0.7
Pension Plan | Equity Securities Preferred
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 1.9		$ 2.1		$ 0.6
Percentage of fair value of plan investments		0.20%		0.20%		0.10%
Pension Plan | Equity Securities Preferred | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 1.9		$ 2.1		$ 0.6
Pension Plan | US Treasury Securities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 133.2		$ 127.6		$ 140.9
Percentage of fair value of plan investments		16.50%		14.80%		16.20%
Pension Plan | US Treasury Securities | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 133.2		$ 127.6		$ 140.9
Pension Plan | Domestic Corporate Debt Securities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 216.4		$ 227.8		$ 232.3
Percentage of fair value of plan investments		26.80%		26.40%		26.60%
Pension Plan | Domestic Corporate Debt Securities | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 216.4		$ 227.8		$ 232.3
Pension Plan | U S Government Agencies And Sponsored Entities Debt Securities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 27.5		$ 28.3		$ 20
Percentage of fair value of plan investments		3.40%		3.30%		2.30%
Pension Plan | U S Government Agencies And Sponsored Entities Debt Securities | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 27.5		$ 28.3		$ 20
Pension Plan | Asset-backed Securities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 0.5		$ 0.5		$ 2
Percentage of fair value of plan investments		0.10%		0.10%		0.20%
Pension Plan | Asset-backed Securities | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 0.5		$ 0.5		$ 2
Pension Plan | Municipalities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 8.3		$ 8.3		$ 14.9
Percentage of fair value of plan investments		1.00%		1.00%		1.70%
Pension Plan | Municipalities | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 8.3		$ 8.3		$ 14.9
Pension Plan | Foreign Corporate Debt Securities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 46.7		$ 47.1		$ 48.1
Percentage of fair value of plan investments		5.80%		5.50%		5.50%
Pension Plan | Foreign Corporate Debt Securities | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 46.7		$ 47.1		$ 48.1
Pension Plan | Repurchase Agreements
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments	[4]					$ 3.7
Percentage of fair value of plan investments	[4]					0.40%
Pension Plan | Fixed Income Securities Other
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments	[5]	$ 4.9		$ 5.2		$ 6.7
Percentage of fair value of plan investments	[5]	0.60%		0.60%		0.80%
Pension Plan | Fixed Income Securities Other | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments	[5]	$ 4.9		$ 5.2		$ 6.7
Pension Plan | Mutual Funds
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments	[6]	$ 36.4		$ 42.4		$ 41.4
Percentage of fair value of plan investments	[6]	4.50%		4.90%		4.70%
Pension Plan | Mutual Funds | Level 1
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments	[6]	$ 36.4		$ 42.4		$ 41.4
Pension Plan | Derivatives
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments	[7]	$ 6.8		$ 1.1		$ 1.9
Percentage of fair value of plan investments	[7]	0.80%		0.10%		0.20%
Pension Plan | Derivatives | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments	[7]	$ 6.8		$ 1.1		$ 1.9
Pension Plan | Commingled Funds And Pooled Separate Accounts
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments	[8],[9]	$ 289.6		$ 329.3		$ 324.4
Percentage of fair value of plan investments	[8],[9]	35.90%		38.00%		37.20%
Pension Plan | Private Equity / Limited Partnership
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments	[9],[10]	$ 35.3		$ 39.1		$ 37.6
Percentage of fair value of plan investments	[9],[10]	4.40%		4.50%		4.30%
Repurchase Agreements | Fixed Income Securities Other | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments	[4]					$ 3.7
Health and Life Benefits
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 124.2		$ 127.1		95.8
Total fair value of plan investments		527.5		568.7		539.8
Receivable (Payable)	[11]	1.3		0.6		0.7
Fair value of plan assets at end of year		$ 528.8		$ 569.3		$ 540.5	$ 505
Percentage of fair value of plan investments		23.50%		22.30%		17.80%
Total fair value of plan assets (%)		99.80%		99.90%		99.90%
Percent Receivable (Payable)	[11]	0.20%		0.10%		0.10%
Total plan assets percent		100.00%		100.00%		100.00%
Health and Life Benefits | Level 1
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 3.2		$ 2.9		$ 2.6
Health and Life Benefits | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		121		124.2		93.2
Health and Life Benefits | Cash and Cash Equivalents
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 3.2		$ 2.9		$ 2.6
Percentage of fair value of plan investments		0.60%		0.50%		0.50%
Health and Life Benefits | Cash and Cash Equivalents | Level 1
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 3.2		$ 2.9		$ 2.6
Health and Life Benefits | US Treasury Securities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 51.2		$ 50.1		$ 36
Percentage of fair value of plan investments		9.70%		8.80%		6.70%
Health and Life Benefits | US Treasury Securities | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 51.2		$ 50.1		$ 36
Health and Life Benefits | Domestic Corporate Debt Securities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 51.6		$ 55		$ 41.9
Percentage of fair value of plan investments		9.80%		9.70%		7.80%
Health and Life Benefits | Domestic Corporate Debt Securities | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 51.6		$ 55		$ 41.9
Health and Life Benefits | US Government Agencies Debt Securities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 1.9		$ 1.9		$ 1.7
Percentage of fair value of plan investments		0.40%		0.30%		0.30%
Health and Life Benefits | US Government Agencies Debt Securities | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 1.9		$ 1.9		$ 1.7
Health and Life Benefits | Municipalities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 4.5		$ 4.7		$ 3.6
Percentage of fair value of plan investments		0.80%		0.80%		0.70%
Health and Life Benefits | Municipalities | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 4.5		$ 4.7		$ 3.6
Health and Life Benefits | Foreign Corporate Debt Securities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 8.5		$ 9.1		$ 7.2
Percentage of fair value of plan investments		1.60%		1.60%		1.30%
Health and Life Benefits | Foreign Corporate Debt Securities | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments		$ 8.5		$ 9.1		$ 7.2
Health and Life Benefits | Fixed Income Securities Other
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments	[12]	$ 3.3		$ 3.4		$ 2.8
Percentage of fair value of plan investments	[12]	0.60%		0.60%		0.50%
Health and Life Benefits | Fixed Income Securities Other | Level 2
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments	[12]	$ 3.3		$ 3.4		$ 2.8
Health and Life Benefits | Commingled Funds
Defined Benefit Plan, Information about Plan Assets [Abstract]
Fair value of plan investments	[13],[14]	$ 403.3		$ 441.6		$ 444
Percentage of fair value of plan investments	[13],[14]	76.30%		77.60%		82.10%
[1]	At December 31, 2018 and September 30, 2018 and 2017, this net payable primarily represents pending trades for investments purchased net of pending trades for investments sold and interest receivable.
[2]	The DB SERP and DB Restoration, included in pension benefits in the table above, does not include the amounts funded in rabbi trust.
[3]	This table does not include rabbi trust investments located in "Current Assets-Other" and "Deferred Charges and Other Assets-Other" on our balance sheets. Refer to
[4]	This category primarily includes non-U.S. government bonds as of December 31, 2018 and September 30, 2018 and 2017.
[5]	This category primarily includes non-U.S. government bonds as of December 31, 2018 and September 30, 2018 and 2017.
[6]	At December 31, 2018 and September 30, 2018 and 2017, the investment in a mutual fund consisted primarily of common stock of non-U.S. based companies.
[7]	At December 31, 2018 and September 30, 2018 and 2017, this category included a combination of long-term U.S. Treasury interest rate future contracts, currency forwards, currency option interest rate swaps, and put and call options on both interest rate swaps and credit default swap index products.
[8]	As of December 31, 2018 investments in commingled funds and a pooled separate account consisted of approximately 89% common stock U.S companies; 9% income producing properties located in the United States; and 1% short-term money market investments. As of September 30, 2018 and 2017, investments in commingled funds and a pooled separate account consisted of approximately 90% common stock U.S companies; 8% income producing properties located in the United States; and 2% short-term money market investments.
[9]	In accordance with ASC Topic 820, these investments are measured at fair value using NAV per share as a practical expedient and, therefore, have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliations of the fair value hierarchy to the statements of net assets available for plan benefits.
[10]	At December 31, 2018 and September 30, 2018 and 2017, investments in a private equity/limited partnership consisted of common stock of international companies.
[11]	September 30, 2018 and 2017, this net receivable primarily represents pending trades for investments sold and interest receivable net of pending trades for investments purchased.
[12]	At December 31, 2018 and September 30, 2018 and 2017, this category consisted primarily of non-U.S. government bonds.
[13]	2018, investments held by commingled funds in which the plan invests consisted primarily of 58% of common stock of large-cap U.S. companies, 17% of U.S. Government fixed income securities and 25% of corporate bonds. At September 30, 2017, investments held by commingled funds in which the plan invests consisted primarily of 67% of common stock of large-cap U.S. companies,13% of U.S. Government fixed income securities and 20% of corporate bonds.
[14]	In accordance with ASC Topic 820, these investments are measured at fair value using Net Asset Value (NAV) per share as a practical expedient and, therefore, have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliations of the fair value hierarchy to the statements of net assets available for plan benefits

Pension and Other Post-retir_12

Pension and Other Post-retirement Benefit Plans (Pension Plan Assets-Footnotes) (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Large Cap U.S. Companies Common Stock | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Allocation of investments in comingled funds and pooled separate accounts	89.00%	90.00%	90.00%
Large Cap U.S. Companies Common Stock | Health and Life Benefits
Defined Benefit Plan Disclosure [Line Items]
Allocation of investments in comingled funds	54.00%	58.00%	67.00%
Income Producing Properties | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Allocation of investments in comingled funds and pooled separate accounts	9.00%	8.00%	8.00%
Short-term money market investments | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Allocation of investments in comingled funds and pooled separate accounts	1.00%	2.00%	2.00%
U.S. governmental and U.S. agency securities [Member] | Health and Life Benefits
Defined Benefit Plan Disclosure [Line Items]
Allocation of investments in comingled funds	20.00%	17.00%	13.00%
Corporate Bonds | Health and Life Benefits
Defined Benefit Plan Disclosure [Line Items]
Allocation of investments in comingled funds	26.00%	25.00%	20.00%

Pension and Other Post-retir_13

Pension and Other Post-retirement Benefit Plans (Expected Benefit Payments) (Details) $ in Millions	Dec. 31, 2018USD ($)
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
2,019	$ 67.5
2,020	53.4
2,021	54.6
2,022	57.7
2,023	56.1
2024—2028	291.2
Health and Life Benefits
Defined Benefit Plan Disclosure [Line Items]
2,019	16.3
2,020	15.7
2,021	15.8
2,022	15.9
2,023	15.9
2024—2028	$ 81.1

Stock-Based Compensation (Narra

Stock-Based Compensation (Narrative) (Details) - USD ($)	Jul. 06, 2018	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Accounts payable and other accrued liabilities-other		$ 31,500,000	$ 51,400,000	$ 12,500,000
Deferred Credits-other		$ 49,147,000	$ 75,046,000	53,537,000
Current Awards | Performance Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value per unit			$ 1
Shares granted during the period		5,934,828
Current Awards | Performance Units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting right percentage			0.00%
Current Awards | Performance Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting right percentage			200.00%
Current Awards | Restricted unit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value per unit			$ 1
Shares granted during the period		2,253,585
Current Awards | Stock Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		$ 300,000
Unrecognized compensation expense		6,500,000
Deferred Credits-other		$ 700,000
Vesting period		2 years 9 months
Prior Awards | Performance Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Liability for Equity Option Awards Outstanding				16,600,000
Cash Paid To Settle Performance Unit Awards		$ 0	$ 8,500,000	6,700,000
Accounts payable and other accrued liabilities-other		2,900,000	$ 2,200,000	8,500,000
Deferred Credits-other				8,100,000
Value per unit			$ 1
Prior Awards | Performance Units | Performance Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value per unit			$ 1
Prior Awards | Stock Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense			$ 15,800,000	12,200,000	$ 10,100,000
Tax benefit from compensation expense			$ 4,900,000	6,100,000	$ 4,500,000
Vesting period			3 years
Prior Awards | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic Value Performance Shares Vested			$ 16,700,000	$ 9,900,000
Vesting period					3 years
Prior Awards | Performance Shares | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting right percentage				0.00%
Prior Awards | Performance Shares | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting right percentage				200.00%
Prior Awards | Modification Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		1,000,000	7,700,000
Unrecognized compensation expense		2,700,000
Deferred Credits-other		$ 3,700,000	3,100,000
Prior Awards | Modification Event | Fiscal years 2017 and 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value per unit	$ 1
Business Acquisition, Share Price	88.25
Cash paid to settle accelerated stock compensation plans			30,000,000
Prior Awards | Modification Event | Fiscal year 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value per unit	1
Business Acquisition, Share Price	$ 88.25
Prior Awards | Directors Stock Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense			$ 800,000	$ 800,000	$ 800,000
Shares authorized for issue under plan			270,000
Shares granted during the period			9,000	10,000	13,000
Weighted-average grant date fair value, vested			$ 85.84	$ 76.28	$ 62.99

Stock-Based Compensation (Perfo

Stock-Based Compensation (Performance Units and Restricted Units) (Details) - Current Awards	3 Months Ended
	Dec. 31, 2018shares
Performance Units
Performance Units and Restricted Units [Roll Forward]
Granted	5,934,828
Non-vested and outstanding, end of year	5,934,828
Restricted unit
Performance Units and Restricted Units [Roll Forward]
Granted	2,253,585
Non-vested and outstanding, end of year	2,253,585

Environmental Matters (Narrativ

Environmental Matters (Narrative) (Details) $ in Thousands		3 Months Ended	12 Months Ended
		Dec. 31, 2018USD ($)site	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)
Site Contingency [Line Items]
Number of Sites | site		10
Estimated maximum liability		$ 29,400	$ 27,300	$ 24,000
Regulatory Assets, Noncurrent		99,105	104,050	104,538
Reserve for Environmental Costs
Site Contingency [Line Items]
Accrual for environmental loss contingencies		11,300	10,200	7,700
Environmental response costs
Site Contingency [Line Items]
Regulatory Assets, Noncurrent	[1],[2]	$ 5,800	$ 5,000	$ 2,500
District of Columbia
Site Contingency [Line Items]
Recovery of environmental response costs term		3 years
[1]	This balance represents allowed environmental remediation expenditures at Washington Gas sites to be recovered through rates for Maryland and the District of Columbia. The recovery period is over several years.
[2]	Washington Gas does not earn its overall rate of return on these assets. Washington Gas is allowed to recover and required to pay, using short-term interest rates, the carrying costs related to billed gas costs due from and to its customers in the District of Columbia and Virginia jurisdictions.

Commitments and Contingencies_2

Commitments and Contingencies (Narrative) (Details)	Jul. 31, 2018USD ($)	Dec. 31, 2018USD ($)company	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Jun. 29, 2018USD ($)	Feb. 01, 2018USD ($)
Commitments and Contingencies [Line Items]
Rent Expense		$ 600,000	$ 5,800,000	$ 5,300,000	$ 5,400,000
Number Of Service Agreements With Pipeline Companies | company		4
Virginia rate case
Commitments and Contingencies [Line Items]
Requested base rate increase	$ 37,600,000
Accelerated pipeline replacement program
Commitments and Contingencies [Line Items]
Requested base rate increase	14,700,000
Tax cuts and jobs act
Commitments and Contingencies [Line Items]
Requested base rate increase	$ (16,300,000)
Tax cuts and jobs act | Maryland
Commitments and Contingencies [Line Items]
Reduction in distribution rates							$ 14,800,000
Tax cuts and jobs act | Virginia
Commitments and Contingencies [Line Items]
Reduction in distribution rates		$ 19,200,000
Tax cuts and jobs act | District of Columbia
Commitments and Contingencies [Line Items]
Reduction in distribution rates						$ 8,300,000
Performance Guarantee | External Partners
Commitments and Contingencies [Line Items]
Guarantees		$ 0

Committments and Contingencies

Committments and Contingencies - Tables (Details) $ in Millions	Dec. 31, 2018USD ($)
Minimum Payments Under Operating Leases
2,018	$ 3
2,019	5.7
2,020	5.3
2,021	5.3
2,022	5.4
Thereafter	50.8
Total	75.5
Gas Purchase Commitments
Contract Minimums
2,018	459.2	[1]
2,019	384.8	[1]
2,020	362	[1]
2,021	353.9	[1]
2,022	339.4	[1]
Thereafter	2,695.7	[1]
Total	4,595	[1]
Pipeline Contracts
Contract Minimums
2,018	373.1	[2]
2,019	374.1	[2]
2,020	366.3	[2]
2,021	362.6	[2]
2,022	362.1	[2]
Thereafter	1,209.6	[2]
Total	$ 3,047.8	[2]
[1]	Includes known and reasonably likely commitments to purchase natural gas. Cost estimates are based on forward market prices at December 31, 2018.
[2]	Represents minimum payments for natural gas transportation, storage and peaking contracts that have expiration dates through calendar year 2044.

Derivative and Weather Relate_4

Derivative and Weather Related Instruments (Details) MMBTU in Millions, $ in Millions		3 Months Ended	12 Months Ended
		Dec. 31, 2018USD ($)MMBTU	Sep. 30, 2018USD ($)MMBTU	Sep. 30, 2017USD ($)MMBTU	Sep. 30, 2016USD ($)
Asset Optimization [Abstract]
Gain (Loss) on Asset Optimization Transactions Net Pretax		$ 1.1	$ 34.3	$ 82.9	$ 43.8
Unrealized Gains (Loss) On Asset Optimization Derivative Instruments Net Pretax		(4.2)	10.4	49.3	$ 12
Derivative, Collateral [Abstract]
Right to Reclaim Cash		7.4	10.6	3.7
Derivative, Collateral, Obligation to Return Cash		0.2	2.7	0.1
Balance Sheet Classification of Derivative Instruments
Gross Derivative Assets	[1]	(38.1)	(27.5)	(24)
Gross Derivative Liabilities	[1]	(144.4)	(123.2)	(145.3)
Netting of Collateral	[1]		2.8
Total	[1],[2]	(106.3)	(92.9)	(121.3)
Current Assets—Derivatives
Balance Sheet Classification of Derivative Instruments
Gross Derivative Assets	[1]	25.7	17.8	7.5
Gross Derivative Liabilities	[1]	(6.2)	(0.4)	(2.4)
Total	[1],[2]	19.5	17.4	5.1
Deferred Charges and Other Assets—Derivatives
Balance Sheet Classification of Derivative Instruments
Gross Derivative Assets	[1]	11.3	8.7	16.5
Gross Derivative Liabilities	[1]			(0.3)
Total	[1],[2]	11.3	8.7	16.2
Current Liabilities—Derivatives
Balance Sheet Classification of Derivative Instruments
Gross Derivative Assets	[1]	1.1	2.6
Gross Derivative Liabilities	[1]	(21.4)	(20.2)	(30.3)
Netting of Collateral	[1]		2.8
Total	[1],[2]	(20.3)	(14.8)	(30.3)
Deferred Credits—Derivatives
Balance Sheet Classification of Derivative Instruments
Gross Derivative Assets	[1]		(1.6)
Gross Derivative Liabilities	[1]	(116.8)	(102.6)	(112.3)
Total	[1],[2]	(116.8)	(104.2)	(112.3)
Credit Risk Contract
Derivative [Line Items]
Derivative liabilities with credit-risk-contingent features		1.1	0.4	2.8
Maximum potential collateral requirements		$ 1	$ 0.4	$ 2.8
Asset optimization & trading
Absolute Notional Amounts of Open Positions on Derivative Instruments
Natural Gas Derivative Transaction, Volume | MMBTU		1,305,100,000	1,358,000,000	1,122,300,000
Other risk-management activities
Absolute Notional Amounts of Open Positions on Derivative Instruments
Natural Gas Derivative Transaction, Volume | MMBTU		107,200,000	106,600,000	118,100,000
[1]	Washington Gas did not have derivative instruments outstanding that were designated as hedging instruments at December 31, 2018, September 30, 2018, or September 30, 2017.
[2]	Washington Gas has elected to offset the fair value of recognized derivative instruments against the right to reclaim or the obligation to return collateral for derivative instruments executed under the same master netting arrangement in accordance with ASC Topic 815. All recognized derivative contracts and associated financial collateral subject to a master netting arrangement or similar that is eligible for offset under ASC Topic 815 have been presented net in the balance sheet.

Derivative and Weather Relate_5

Derivative and Weather Related Instruments (Gains and Losses) (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Gains and (Losses) on Derivative Instruments
Total		$ (9,200)		$ (9,700)	$ 127,300	$ 18,700
Interest Expense		15,706	$ 14,973	58,504	52,207	41,444
Utility cost of gas
Gains and (Losses) on Derivative Instruments
Recorded to income		(3,200)		(2,100)	50,100	12,100
Gas costs
Gains and (Losses) on Derivative Instruments
Recorded to regulatory assets/liabilities		$ (6,000)		$ (7,600)	$ 77,200	13,900
Other
Gains and (Losses) on Derivative Instruments
Recorded to regulatory assets/liabilities	[1]					$ (7,300)
[1]	Represents the settlement of Washington Gas' forward starting interest rate swap in September 2016.

Derivative and Weather Relate_6

Derivative and Weather Related Instruments (Details 2) $ in Millions	Dec. 31, 2018USD ($)Counterparties	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)
Derivative [Line Items]
Number of Counterparties | Counterparties	3
Percentage Of Credit Exposure	10.00%
Obligation to counterparties	$ 41.6
Credit Risk Contract
Derivative [Line Items]
Derivative liabilities with credit-risk-contingent features	1.1	$ 0.4	$ 2.8
Maximum potential collateral requirements	$ 1	$ 0.4	$ 2.8

Fair Value Measurements Under t

Fair Value Measurements Under the Fair Value Hierarchy (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Assets	$ 38.1	$ 27.5	$ 24
Liabilities	(144.4)	(123.2)	(145.3)
Natural Gas Related Derivatives
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Assets	38.1	27.5	24
Liabilities	(144.4)	(123.2)	(145.3)
Level 2
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Assets	9.8	3.9	7
Liabilities	(9.5)	(5.5)	(5.7)
Level 2 | Natural Gas Related Derivatives
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Assets	9.8	3.9	7
Liabilities	(9.5)	(5.5)	(5.7)
Level 3
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Assets	28.3	23.6	17
Liabilities	(134.9)	(117.7)	(139.6)
Level 3 | Natural Gas Related Derivatives
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Assets	28.3	23.6	17
Liabilities	$ (134.9)	$ (117.7)	$ (139.6)

Fair Value Measurements (Quanti

Fair Value Measurements (Quantitative information) (Details) - Natural Gas Related Derivatives - USD ($)	Dec. 31, 2018	Oct. 01, 2018	Sep. 30, 2018	Oct. 01, 2017	Sep. 30, 2017	Sep. 30, 2016
Fair Value Measurements Details [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	$ (106,600,000)	$ (94,100,000)	$ (94,100,000)	$ (122,600,000)	$ (122,600,000)	$ (251,600,000)
Discounted Cash Flow
Fair Value Measurements Details [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	(106,600,000)		(94,100,000)		(122,600,000)
Discounted Cash Flow | Maximum | Natural Gas Basis Price
Fair Value Measurements Details [Line Items]
Input Price	5.34		3.886		2.805
Discounted Cash Flow | Minimum | Natural Gas Basis Price
Fair Value Measurements Details [Line Items]
Input Price	$ (1.028)		$ (1.003)		$ (1.928)

Fair Value Measurements (Reconc

Fair Value Measurements (Reconciliation with Level 3 Inputs) (Details) - Natural Gas Related Derivatives - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs
Beginning Balance	$ (94.1)	$ (122.6)	$ (251.6)
Recorded to Income	(4.4)	(4.5)	44.2
Recorded to regulatory assets - gas costs	(5.8)	(10)	69.7
Transfers into Level 3		(6.9)	(0.4)
Transfers out of Level 3		8.9	(0.4)
Settlements	(2.3)	41	15.9
Ending Balance	$ (106.6)	$ (94.1)	$ (122.6)

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Commercial Paper		$ 311,460	$ 163,478	$ 166,772
Current maturities of long-term debt		50,000	50,000	0
Long-term debt		1,035,033	1,084,933	1,134,461
Restricted cash included in Current assets-Other		20,347	20,347	102
Restricted cash included in Deferred Charges and Other Assets-Other		50,490	49,331	3,561
Cash and Cash Equivalents
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Money Market Funds		4,400	2,300
Rabbi Trusts
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Restricted cash included in Current assets-Other		20,207	20,207	0	$ 0
Restricted cash included in Deferred Charges and Other Assets-Other		45,134	44,775	0	$ 0
Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Money Market Funds	[1]	69,700	67,300	4,800
Commercial Paper	[2]	296,000	95,000	123,000
Project financing	[2]	15,500	68,500	43,800
Current maturities of long-term debt		50,000	50,000
Long-term debt	[3]	1,035,000	1,084,900	1,134,500
Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Money Market Funds	[1]	69,700	67,300	4,800
Commercial Paper	[2]	296,000	95,000	123,000
Project financing	[2]	15,500	68,500	43,800
Long-term debt	[3]	1,096,300	1,120,200	$ 1,271,000
Current maturities of long-term debt		$ 50,000	$ 50,000
[1]	The balance as of September 30, 2018 includes $2.3 million money market funds located in "Cash and cash equivalents", $20.2 million rabbi trust investment located in "Current Assets-Other" and $44.8 million rabbi trust investments located in "Deferred Charges and Other Assets-Other" ; The balance as of September 2017 is located in "Cash and cash equivalents". The amounts in cash and cash equivalent may be offset by outstanding checks.
[2]	Balance is located in "Notes payable and project financing" in the accompanying balance sheets.
[3]	Includes adjustments for current maturities and unamortized discounts, as applicable.

Fair Value Measurements (Realiz

Fair Value Measurements (Realized and Unrealized Gains and Losses with Level 3 Measurements) (Details) - Natural Gas Related Derivatives - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Unrealized Gains (Losses) Recorded for Level 3 Measurements
Recorded to regulatory assets - gas costs	$ (5.8)	$ (10)	$ 69.7
Total Unrealized Gains (Losses)	(9.3)	2.5	82	$ (2.3)
Utility cost of gas
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements
Recorded to income	(4.4)	(4.5)	44.2	4
Unrealized Gains (Losses) Recorded for Level 3 Measurements
Recorded to income	(4)	2.3	31	0.3
Regulatory asset-gas costs member
Unrealized Gains (Losses) Recorded for Level 3 Measurements
Recorded to regulatory assets - gas costs	$ (5.3)	$ 0.2	$ 51	$ (2.6)

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($)		3 Months Ended		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Oct. 01, 2018
Related Party Transaction [Line Items]
Current liabilities-other		$ 7,507,000		$ 7,627,000	$ 7,473,000
Operation and maintenance		102,728,000	$ 82,372,000	544,180,000	340,604,000	$ 329,303,000
Receivables from Associated Companies		4,819,000		2,227,000	32,362,000
Payables to associated companies		95,228,000		21,548,000	94,844,000		$ 53,000,000
Shared service costs
Related Party Transaction [Line Items]
Operation and maintenance		4,500,000		4,000,000
Receivables from Associated Companies		600,000		1,100,000
Payables to associated companies		0		5,100,000
Other associated companies
Related Party Transaction [Line Items]
Receivables from Associated Companies	[1]	4,200,000		1,100,000	32,400,000
Payables to associated companies	[1]	95,200,000		16,400,000	94,800,000
Hampshire Gas Company
Related Party Transaction [Line Items]
Operation and maintenance		1,700,000		6,900,000	6,800,000	6,400,000
WGL Energy Services
Related Party Transaction [Line Items]
Receivables from Associated Companies		700,000
Payables to associated companies				1,500,000	1,400,000
Gas balancing service charge		4,600,000		18,500,000	23,600,000	$ 26,800,000
Related Party Purchased Receivables		$ 6,400,000		$ 2,800,000	$ 3,200,000
[1]	The receivables and payables do not include the transactions related to shared service cost billed from AltaGas.

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2018		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2016
AOCI, Net of Tax [Roll Forward]
Beginning Balance		$ (1,830)		$ (4,522)		$ (7,830)
Change in prior service cost	$ (26,100)	(226)	[1]	(675)	[1]	(767)	[1]	$ (891)
Amortization of actuarial gain (loss)		(6,246)	[1]	6,324	[1]	6,232	[1]	(936)
Current-period other comprehensive income (loss)		(6,472)		5,649		5,465
Income tax expense related to other comprehensive income (loss)		(1,675)		2,957		2,157		(709)
Ending Balance		$ (6,627)		$ (1,830)		$ (4,522)		$ (7,830)
[1]	These accumulated other comprehensive income (loss) components are included in the computation of net periodic benefit cost. Refer to Note 9—Pension and other post-retirement benefit plans for additional details.

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Increase (Decrease) in Operating Capital [Abstract]
Accounts receivable and unbilled revenues	$ (222,098)	$ (13,557)	$ (107,195)	$ (67,681)
Receivables from associated companies	(1,874)	30,135	(18,563)	(10,623)
Gas costs and other regulatory assets/liabilities—net	40,028	27,994	3,430	(31,075)
Storage gas	(2,550)	(8,626)	(10,280)	12,016
Prepaid taxes	(9,461)	5,618	(6,524)	13,539
Accounts payable and other accrued liabilities	61,029	18,378	17,921	34,261
Payables to associated companies	20,662	(73,296)	29,074	(2,853)
Customer deposits and advance payments	(29,288)	19,464	(16,742)	(7,514)
Accrued taxes	1,024	14,619	(4,831)	5,980
Other current assets	(28)	(14,605)	(4,123)	3,912
Other current liabilities	(121)	154	280	(1,318)
Deferred gas costs—net	(51,936)	(8,306)	2,467	(5,104)
Deferred assets—other	483	(5,895)	(15,088)	(22,057)
Deferred liabilities—other	(7,072)	(21,499)	(4,667)	(56,865)
Pension and other post-retirement benefits	(638)	(14,521)	(9,806)	(10,251)
Other—net	0	893	3,409	2,107
Changes in operating assets and liabilities	(201,840)	(43,050)	(141,238)	(143,526)
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Income taxes paid (refunded)—net	3,782	(2,983)	0	(19,004)
Interest paid	4,982	57,036	50,539	40,972
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Extinguishment of project debt financing	(53,018)	(28,312)	(27,927)	0
Capital expenditure accruals included in accounts payable and other accrued liabilities	33,245	53,367	37,049	43,687
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	6,082	1	1	1
Restricted cash included in Current assets-Other	20,347	20,347	102
Restricted cash included in Deferred Charges and Other Assets-Other	50,490	49,331	3,561
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	71,423	64,983	1	1	$ 1
Rabbi Trusts
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Restricted cash included in Current assets-Other	20,207	20,207	0	0
Restricted cash included in Deferred Charges and Other Assets-Other	$ 45,134	$ 44,775	$ 0	$ 0

Merger with AltaGas Ltd. (Detai

Merger with AltaGas Ltd. (Details) - USD ($) $ in Thousands

Sep. 30, 2028

Sep. 30, 2023

Sep. 30, 2021

Jul. 06, 2018

Jan. 25, 2017

Dec. 31, 2018

Sep. 30, 2018

Dec. 31, 2017

Sep. 30, 2018

Sep. 30, 2017

Sep. 30, 2016

Business Acquisition [Line Items]

Business Acquisition, Effective Date of Acquisition

Jul. 6, 2018

Other income (expense) —net

$ 3,494

$ 1,029

$ (7,592)

$ (545)

$ 1,434

Operation and Maintenance Expenses

102,728

$ 82,372

544,180

$ 340,604

$ 329,303

Customer bill credits

Business Acquisition [Line Items]

Operation and Maintenance Expenses

$ 56,800

Merger commitment paid in fiscal year 2018

$ 56,800

56,800

Gas expansion fund contributions

Business Acquisition [Line Items]

Operation and Maintenance Expenses

34,200

30,300

Merger commitment expected to be paid in 2019

3,900

Energy customer or education programs

Business Acquisition [Line Items]

Operation and Maintenance Expenses

22,800

Merger commitment paid in fiscal year 2018

22,800

22,800

Charitable contributions

Business Acquisition [Line Items]

Operation and Maintenance Expenses

13,500

800

Merger commitment paid in fiscal year 2018

400

400

Merger commitment expected to be paid in 2019

2,800

Merger commitment expected to be paid in 2020

1,500

Merger commitment expected to be paid in 2021

1,500

Merger commitment expected to be paid in 2022

1,500

Merger commitment expected to be paid in 2023

1,500

Merger commitment expected to be paid in 2024-2027

3,500

Work place development initiatives

Business Acquisition [Line Items]

Operation and Maintenance Expenses

7,800

Merger commitment expected to be paid in 2019

3,800

Merger commitment expected to be paid in 2020

3,800

Merger commitment expected to be paid in 2021

100

Merger commitment expected to be paid in 2022

100

Merger commitment expected to be paid in 2023

100

Low-income weatherization and energy efficiency initiatives

Business Acquisition [Line Items]

Operation and Maintenance Expenses

4,200

Merger commitment expected to be paid in 2019

2,100

Merger commitment expected to be paid in 2020

2,100

Public safety programs

Business Acquisition [Line Items]

Operation and Maintenance Expenses

700

Merger commitment expected to be paid in 2019

700

Total

Business Acquisition [Line Items]

Operation and Maintenance Expenses

$ 140,000

31,100

Merger commitment paid in fiscal year 2018

80,000

80,000

Merger commitment expected to be paid in 2019

13,300

Merger commitment expected to be paid in 2020

7,400

Merger commitment expected to be paid in 2021

1,600

Merger commitment expected to be paid in 2022

1,600

Merger commitment expected to be paid in 2023

1,600

Merger commitment expected to be paid in 2024-2027

3,500

Rabbi trusts contribution

Business Acquisition [Line Items]

Merger commitment

66,700

66,700

Merger costs

Business Acquisition [Line Items]

Other income (expense) —net

13,500

Operation and Maintenance Expenses

3,300

$ 200,200

186,700

Merger commitments

Business Acquisition [Line Items]

Operation and Maintenance Expenses

[1]

400

139,600

Property plant and equipment impairment

Business Acquisition [Line Items]

Operation and Maintenance Expenses

[2]

38,000

Key employee retention payments

Business Acquisition [Line Items]

Operation and Maintenance Expenses

10,500

Acceleration of stock-based compensation

Business Acquisition [Line Items]

Operation and Maintenance Expenses

[3]

5,400

Severance costs

Business Acquisition [Line Items]

Operation and Maintenance Expenses

[4]

$ 2,900

6,700

Total

Business Acquisition [Line Items]

Operation and Maintenance Expenses

$ 200,200

AltaGas Ltd.

Business Acquisition [Line Items]

Business Acquisition, Date of Acquisition Agreement

Jan. 25, 2017

Business Acquisition, Effective Date of Acquisition

Jul. 6, 2018

Scenario, Forecast | Future hiring

Business Acquisition [Line Items]

Operation and Maintenance Expenses

$ 2,400

Scenario, Forecast | Future capital plan investments

Business Acquisition [Line Items]

Operation and Maintenance Expenses

$ 70,000

Scenario, Forecast | Future leak mitigation

Business Acquisition [Line Items]

Operation and Maintenance Expenses

$ 8,000

[1]

See the Merger Commitments table below for details of merger related commitments.

[2]

Net property, plant and equipment impairment recorded in connection with an agreement not to seek recovery of certain costs incurred under the Formal Case 1027 mechanical coupling program.

[3]

See Note 10-Stock-Based Compensation for further discussion of the acceleration of incentive compensation.

[4]

Severance costs are related to the retirement of senior executives following the merger.

Transiction Period Comparative

Transiction Period Comparative Data (Details) - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	[1]	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Transition Period Comparative Data [Abstract]
OPERATING REVENUES	$ 402,101					$ 377,470				$ 1,248,063	$ 1,166,968	$ 1,070,904
Utility cost of gas	156,641					124,745				407,043	297,856	271,975
Operation and maintenance	102,728					82,372				544,180	340,604	329,303
Depreciation and amortization	34,948					33,646				135,071	129,428	114,605
General taxes and other assessments	38,552					39,983				148,178	134,696	130,231
Total Operating Expenses	332,869					280,746				1,234,472	902,584	846,114
Operating income (loss)	69,232	$ (225,462)		$ (6,649)	$ 148,978	96,724	$ (13,000)	$ 10,482	$ 164,876	13,591	264,384	224,790
Other income (expense) —net	3,494					1,029				(7,592)	(545)	1,434
Interest expense	15,706					14,973				58,504	52,207	41,444
INCOME BEFORE INCOME TAXES	57,020					82,780				(52,505)	211,632	184,780
Income tax expense (benefit)	7,847					24,854				(25,863)	79,840	71,666
NET INCOME	49,173	(181,153)		(11,499)	108,084	57,926	(15,608)	(1,671)	93,610	(26,642)	131,792	113,114
Dividends on preferred stock	330					330				1,320	1,320	1,320
NET INCOME APPLICABLE TO COMMON STOCK	$ 48,843	$ (181,483)		$ (11,829)	$ 107,754	$ 57,596	$ (15,938)	$ (2,001)	$ 93,280	$ (27,962)	$ 130,472	$ 111,794
[1]	During the quarter ended September 30, 2018, Washington Gas recorded $200.2 million of merger related costs due to the Merger with AltaGas.

Quarterly Financial Data - Tabl

Quarterly Financial Data - Table (Details) - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018		Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Operating revenues	$ 402,101	$ 139,041	[1]	$ 199,512	$ 532,040	$ 377,470	$ 154,775	$ 203,186	$ 475,021
Operating income (loss)	69,232	(225,462)	[1]	(6,649)	148,978	96,724	(13,000)	10,482	164,876	$ 13,591	$ 264,384	$ 224,790
NET INCOME (LOSS)	49,173	(181,153)	[1]	(11,499)	108,084	57,926	(15,608)	(1,671)	93,610	(26,642)	131,792	113,114
Net income (loss) applicable to common stock	48,843	(181,483)	[1]	$ (11,829)	$ 107,754	57,596	$ (15,938)	$ (2,001)	$ 93,280	(27,962)	130,472	111,794
Operation and Maintenance Expenses	102,728					$ 82,372				544,180	$ 340,604	$ 329,303
Merger costs
Operation and Maintenance Expenses	$ 3,300	$ 200,200								$ 186,700
[1]	During the quarter ended September 30, 2018, Washington Gas recorded $200.2 million of merger related costs due to the Merger with AltaGas.

Schedule II (Details)

Schedule II (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Beginning Balance		$ 29,622	$ 23,741	$ 20,220	$ 19,254
Valuation Allowances and Reserves, Charged to Cost and Expense	[1]	5,902	19,946	14,320	10,946
Valuation Allowances and Reserves, Charged to Other Accounts	[2]	581	1,409	1,821	3,806
Valuation Allowances and Reserves, Deduction	[3]	6,644	15,474	12,620	13,786
Valuation Allowances and Reserves, Ending Balance		$ 29,461	$ 29,622	$ 23,741	$ 20,220
[1]	Represent the amount of bad debt expense recorded to the income statement.
[2]	Recoveries on receivables previously written off as uncollectible and unclaimed customer deposits, overpayments, etc. non refundable.
[3]	Includes deductions for accounts charged-off.