Washington Gas Light (WGLCP) 10-K 21 Nov 14 2014 Q4 Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Oct. 31, 2014	Mar. 31, 2014
Document and Entity Information [Abstract]	'	'	'
Entity Registrant Name	'WGL Holdings Inc.	'	'
Entity Central Index Key	'0001103601	'	'
Document Type	'10-K	'	'
Document Period End Date	30-Sep-14	'	'
Amendment Flag	'false	'	'
Document Fiscal Year Focus	'2014	'	'
Document Fiscal Period Focus	'Q4	'	'
Current Fiscal Year End Date	'--09-30	'	'
Entity Well-known Seasoned Issuer	'Yes	'	'
Entity Voluntary Filers	'No	'	'
Entity Current Reporting Status	'Yes	'	'
Entity Filer Category	'Large Accelerated Filer	'	'
Entity Public Float	'	'	$2,064,823,797
Entity Common Stock, Shares Outstanding	'	49,708,750	'

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Sep. 30, 2014		Sep. 30, 2013
In Thousands, unless otherwise specified
Capitalization	'		'
Long-Term Debt	$679,300	[1]	'
Current Liabilities	'		'
Notes payable	453,500		373,100
WGL Holdings, Inc.	'		'
Property, Plant and Equipment	'		'
At original cost	4,582,764		4,118,149
Accumulated depreciation and amortization	-1,268,319		-1,210,686
Net property, plant and equipment	3,314,445		2,907,463
Current Assets	'		'
Cash and cash equivalents	8,811		3,478
Receivables	'		'
Accounts receivable	222,253		229,544
Gas costs and other regulatory assets	3,752		10,825
Unbilled revenues	96,314		98,598
Allowance for doubtful accounts	-23,341		-20,433
Net receivables	298,978		318,534
Materials and supplies-principally at average cost	23,647		24,904
Storage gas	333,602		347,291
Deferred income taxes	26,664		24,522
Prepaid taxes	66,578		24,450
Other prepayments	34,269		29,922
Derivatives	18,331		35,315
Other	24,635		11,595
Total current assets	835,515		820,011
Deferred Charges and Other Assets	'		'
Gas costs	191,346		93,963
Pension and other post-retirement benefits	192,981		240,634
Other	71,638		66,010
Prepaid post-retirement benefits	96,385		0
Derivatives	18,739		26,306
Investments in direct financing leases, capital leases	18,159		23,390
Investments in unconsolidated affiliates	100,528		67,522
Other	16,763		14,761
Total deferred charges and other assets	706,539		532,586
Total Assets	4,856,499		4,260,060
Capitalization	'		'
Common shareholders' equity	1,246,576		1,274,545
Washington Gas Light Company preferred stock	28,173		28,173
Long-Term Debt	679,228		524,067
Total capitalization	1,953,977		1,826,785
Current Liabilities	'		'
Current maturities of long-term debt	20,000		67,000
Notes payable	453,500		373,100
Accounts payable and other accrued liabilities	313,221		270,658
Wages payable	19,995		18,645
Accrued interest	3,488		3,399
Dividends declared	22,449		22,075
Customer deposits and advance payments	68,318		67,154
Gas costs and other regulatory liabilities	22,563		27,013
Accrued taxes	14,133		16,056
Derivatives	48,555		48,413
Other	34,063		36,564
Total current liabilities	1,020,285		950,077
Deferred Credits	'		'
Unamortized investment tax credits	99,351		46,378
Deferred income taxes	660,908		629,807
Accrued pensions and benefits	120,446		148,890
Asset retirement obligations	175,203		101,321
Regulatory liabilities	'		'
Accrued asset removal costs	327,388		321,266
Other post-retirement benefits	86,428		0
Other	17,588		13,459
Derivatives	294,745		141,334
Other	100,180		80,743
Total deferred credits	1,882,237		1,483,198
Total Capitalization and Liabilities	4,856,499		4,260,060
Washington Gas Light Company	'		'
Property, Plant and Equipment	'		'
At original cost	4,250,194		3,903,482
Accumulated depreciation and amortization	-1,228,130		-1,178,600
Net property, plant and equipment	3,022,064		2,724,882
Current Assets	'		'
Cash and cash equivalents	1,060		0
Receivables	'		'
Accounts receivable	121,419		91,405
Gas costs and other regulatory assets	3,752		10,825
Unbilled revenues	20,881		19,418
Allowance for doubtful accounts	-19,209		-17,498
Net receivables	126,843		104,150
Materials and supplies-principally at average cost	23,600		24,857
Storage gas	156,083		132,226
Deferred income taxes	22,916		27,000
Prepaid taxes	16,137		14,868
Other prepayments	14,272		7,926
Receivables from associated companies	4,821		7,173
Derivatives	3,884		4,278
Total current assets	369,616		322,478
Deferred Charges and Other Assets	'		'
Gas costs	191,346		93,963
Pension and other post-retirement benefits	191,896		239,434
Other	71,584		65,984
Prepaid post-retirement benefits	95,660		0
Derivatives	9,455		16,051
Other	13,457		11,597
Total deferred charges and other assets	573,398		427,029
Total Assets	3,965,078		3,474,389
Capitalization	'		'
Common shareholders' equity	1,050,166		1,024,583
Washington Gas Light Company preferred stock	28,173		28,173
Long-Term Debt	679,228		524,067
Total capitalization	1,757,567		1,576,823
Current Liabilities	'		'
Current maturities of long-term debt	20,000		67,000
Notes payable	89,000		124,500
Accounts payable and other accrued liabilities	176,467		132,814
Wages payable	18,290		17,057
Accrued interest	3,488		3,399
Dividends declared	19,722		19,359
Customer deposits and advance payments	68,318		67,154
Gas costs and other regulatory liabilities	22,563		27,013
Accrued taxes	24,610		25,380
Payables to associated companies	54,685		20,557
Derivatives	33,858		24,749
Other	7,199		9,047
Total current liabilities	538,200		538,029
Deferred Credits	'		'
Unamortized investment tax credits	6,479		7,354
Deferred income taxes	619,946		611,453
Accrued pensions and benefits	118,954		147,479
Asset retirement obligations	173,775		99,972
Regulatory liabilities	'		'
Accrued asset removal costs	327,388		321,266
Other post-retirement benefits	85,814		0
Other	17,588		13,459
Derivatives	260,789		106,144
Other	58,578		52,410
Total deferred credits	1,669,311		1,359,537
Total Capitalization and Liabilities	$3,965,078		$3,474,389
[1]	Excludes unamortized discounts of $121,567 at September 30, 2014.

Consolidated_Statements_of_Inc

Consolidated Statements of Income (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
WGL Holdings, Inc.	'		'		'
OPERATING REVENUES	'		'		'
Utility	$1,416,951		$1,174,724		$1,109,355
Non-utility	1,363,996		1,291,414		1,315,955
Total Operating Revenues	2,780,947	[1]	2,466,138	[1]	2,425,310	[1]
OPERATING EXPENSES	'		'		'
Utility cost of gas	700,305		496,487		394,955
Non-utility cost of energy-related sales	1,255,279		1,187,844		1,190,093
Operation and maintenance	365,873		366,889		342,810
Depreciation and amortization	110,772		103,284		96,476
General taxes and other assessments	151,196		145,816		135,455
Total Operating Expenses	2,583,425		2,300,320		2,159,789
OPERATING INCOME (LOSS)	197,522		165,818		265,521
Equity in earnings of unconsolidated affiliates	3,194		1,510		1,240
Other Income (Expense) - Net	1,536		2,548		4,154
Interest Expense	37,738		36,011		36,428
INCOME (LOSS) BEFORE INCOME TAXES	164,514		133,865		234,487
INCOME TAX EXPENSE (BENEFIT)	57,254		52,292		93,349
Net income	107,260		81,573		141,138
Dividends on Washington Gas Light Company preferred stock	1,320		1,320		1,320
NET INCOME (LOSS) APPLICABLE TO COMMON STOCK	105,940		80,253		139,818
AVERAGE COMMON SHARES OUTSTANDING	'		'		'
Basic	51,759		51,697		51,522
Diluted	51,770		51,808		51,589
EARNINGS PER AVERAGE COMMON SHARE	'		'		'
Basic	$2.05		$1.55		$2.71
Diluted	$2.05		$1.55		$2.71
DIVIDENDS DECLARED PER COMMON SHARE	$1.74		$1.66		$1.59
Washington Gas Light Company	'		'		'
OPERATING REVENUES	'		'		'
Total Operating Revenues	1,443,800		1,200,357		1,137,666
OPERATING EXPENSES	'		'		'
Utility cost of gas	726,879		521,508		421,539
Operation and maintenance	294,613		295,664		282,746
Depreciation and amortization	102,713		99,188		93,811
General taxes and other assessments	137,472		133,391		124,814
Total Operating Expenses	1,261,677		1,049,751		922,910
OPERATING INCOME (LOSS)	182,123		150,606		214,756
Other Income (Expense) - Net	862		1,544		3,135
Interest Expense	37,127		35,631		36,098
INCOME (LOSS) BEFORE INCOME TAXES	145,858		116,519		181,793
INCOME TAX EXPENSE (BENEFIT)	47,534		44,197		71,747
Net income	98,324		72,322		110,046
Dividends on Washington Gas Light Company preferred stock	1,320		1,320		1,320
NET INCOME (LOSS) APPLICABLE TO COMMON STOCK	$97,004		$71,002		$108,726
[1]	Operating revenues are reported gross of revenue taxes. Revenue taxes of both the regulated utility and the retail energy-marketing segments include gross receipt taxes. Revenue taxes of the regulated utility segment also include PSC fees, franchise fees and energy taxes. Operating revenue amounts in the "Eliminations" column represent total intersegment revenues associated with sales from the regulated utility segment to the retail energy-marketing segment. Midstream Energy Services' cost of energy related sales is netted with its gross revenues.

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
WGL Holdings, Inc.	'		'		'
Net Income	$107,260		$81,573		$141,138
Qualified cash flow hedging instruments	-1,548	[1]	0		0
Pension and other post-retirement benefit plans	'		'		'
Change in prior service cost (credit)	6,095	[2],[3]	-1,671	[2]	-640
Change in actuarial net gain (loss)	1,594	[2]	3,399	[2]	-2,125
Change in transition obligation	0	[2]	238	[2]	239
TOTAL OTHER COMPREHENSIVE INCOME (LOSS) BEFORE TAXES	6,141		1,966		-2,526
INCOME TAX EXPENSE (BENEFIT) RELATED TO OTHER COMPREHENSIVE INCOME	3,054	[3]	813		-987
OTHER COMPREHENSIVE INCOME (LOSS)	3,087		1,153		-1,539
COMPREHENSIVE INCOME	110,347		82,726		139,599
Washington Gas Light Company	'		'		'
Net Income	98,324		72,322		110,046
Pension and other post-retirement benefit plans	'		'		'
Change in prior service cost (credit)	6,095	[2],[3]	-1,671	[2]	-640
Change in actuarial net gain (loss)	1,594	[2]	3,399	[2]	-2,125
Change in transition obligation	0	[2]	238	[2]	239
TOTAL OTHER COMPREHENSIVE INCOME (LOSS) BEFORE TAXES	7,689		1,966		-2,526
INCOME TAX EXPENSE (BENEFIT) RELATED TO OTHER COMPREHENSIVE INCOME	3,054	[3]	813		-987
OTHER COMPREHENSIVE INCOME (LOSS)	4,635		1,153		-1,539
COMPREHENSIVE INCOME	$102,959		$73,475		$108,507
[1]	(c ) Cash flow hedging instruments represent interest rate swap agreements on debt issuances. Refer to Note 14 - Derivative and Weather-related Instruments for further discussion of the interest rate swap agreements.
[2]	(a) These accumulated other comprehensive income components are included in the computation of net periodic benefit cost. Refer to Note 10-Pension and other post-retirement benefit plans for additional details.
[3]	(b) The majority of the 2014 change to the prior service cost component of other comprehensive income is related to the impact of the OPEB plan amendment and re-measurement. Refer to Note 10-Pension and other post-retirement benefit plans for additional details.

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
	WGL Holdings, Inc.	WGL Holdings, Inc.	WGL Holdings, Inc.	Washington Gas Light Company	Washington Gas Light Company	Washington Gas Light Company
OPERATING ACTIVITIES	'	'	'	'	'	'
Net income	$107,260	$81,573	$141,138	$98,324	$72,322	$110,046
ADJUSTMENTS TO RECONCILE NET INCOME TO NET CASH PROVIDED BY OPERATING ACTIVITIES	'	'	'	'	'	'
Depreciation and amortization	110,772	103,284	96,476	102,713	99,188	93,811
Amortization of:	'	'	'	'	'	'
Other regulatory assets and liabilities-net	610	574	881	610	911	881
Debt related costs	886	873	894	886	527	894
Deferred income taxes-net	25,795	1,431	107,699	7,050	-2,915	89,132
Accrued/deferred pension and other post-retirement benefit cost	33,384	36,127	-60,459	33,670	35,707	-58,645
Compensation expense related to stock-based awards	4,105	3,050	4,122	3,185	2,292	3,394
Provision for doubtful accounts	14,252	9,258	18,316	11,839	7,183	12,794
Impairment loss	2,639	2,600	5,015	2,639	2,600	5,015
Other non-cash charges (credits)-net	-3,079	2,536	-5,151	8,838	7,615	-2,726
CHANGES IN ASSETS AND LIABILITIES	'	'	'	'	'	'
Accounts receivable and unbilled revenues-net	-1,769	12,105	-65,329	-39,253	-464	-19,041
Gas costs and other regulatory assets/liabilities-net	2,623	36,359	-13,650	2,623	36,359	-13,650
Storage gas	13,689	-64,283	7,386	-23,857	-17,400	51,228
Prepaid Taxes	-42,128	33,506	-36,643	-1,269	31,937	-32,546
Accounts payable and other accrued liabilities	21,326	2,017	-16,683	49,429	-24,949	27,214
Customer deposits and advance payments	1,164	-22,166	11,181	1,164	-22,166	11,181
Accrued taxes	-1,923	-6,980	6,111	-770	6,272	-3,721
Unamortized investment tax credits	56,639	19,296	14,736	'	'	'
Other current assets	-16,130	-2,513	-5,768	-5,089	5,843	2,964
Other current liabilities	-1,062	22,106	27,297	-526	19,253	3,676
Deferred gas costs-net	-97,383	-113,474	36,309	-97,383	-113,474	36,309
Deferred assets-other	-7,525	-133	-51,889	-10,073	-757	-43,553
Deferred liabilities-other	-3,130	45	-5,230	-3,007	-966	-23,887
Derivatives	178,104	163,571	-1,858	170,744	137,559	-3,608
Pension and other post-retirement benefits	-16,602	-4,417	10,613	-16,973	-4,261	10,786
Other-net	-350	1,679	-7,915	-359	-4,167	-1,673
Net Cash Provided by (Used in) Operating Activities	382,167	318,024	217,599	295,155	274,049	256,275
FINANCING ACTIVITIES	'	'	'	'	'	'
Common stock issued	714	0	631	'	'	'
Long-term debt issued	175,253	4,157	0	175,253	4,157	0
Long-term debt retired	-67,000	-2,295	-77,000	-67,000	-2,295	-77,000
Debt issuance costs	-1,543	0	-123	-1,543	0	0
Notes payable issued (retired)-net	80,400	125,400	208,279	-35,500	25,700	98,778
Dividends on common stock and preferred stock	-85,901	-86,078	-77,182	-79,665	-76,522	-75,239
Repurchase of common stock	-56,136	0	0	'	'	'
Other financing activities-net	-560	5,156	564	-1,749	336	2,533
Net Cash Provided by (Used in) Financing Activities	45,227	46,340	55,169	-10,204	-48,624	-50,928
INVESTING ACTIVITIES	'	'	'	'	'	'
Capital expenditures (excluding AFUDC)	-394,762	-312,345	-251,128	-283,891	-225,426	-206,699
Investments in non-utility interests	-31,415	-62,894	-24,636	'	'	'
Distributions from non-utility interests	4,116	4,090	8,927	'	'	'
Net Cash Used in Investing Activities	-422,061	-371,149	-266,837	-283,891	-225,426	-206,699
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	5,333	-6,785	5,931	1,060	-1	-1,352
Cash and Cash Equivalents at Beginning of Year	3,478	10,263	4,332	0	1	1,353
Cash and Cash Equivalents at End of Year	8,811	3,478	10,263	1,060	0	1
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION	'	'	'	'	'	'
Income taxes paid (refunded) - net	20,110	-10,741	23,915	19,007	-15,799	29,625
Interest paid	36,991	35,471	36,777	36,380	35,091	36,447
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING ACTIVITIES	'	'	'	'	'	'
Project debt financing activities - net	253	1,386	2,004	253	1,386	2,004
Capital expenditure accruals included in accounts payable and other accrued liabilities	55,164	32,040	34,980	46,331	16,429	22,909
Dividends paid in common stock	$5,312	$6,863	$5,260	'	'	'

Consolidated_Statement_of_Capi

Consolidated Statement of Capitalization - WGLH (WGL Holdings, Inc., USD $)

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Series One [Member]

Series One [Member]

Series Two [Member]

Series Two [Member]

Series Three [Member]

Series Three [Member]

Due fiscal year 2014

Due fiscal year 2014

Due fiscal year 2015

Due fiscal year 2015

Due fiscal year 2016

Due fiscal year 2016

Due fiscal year 2019

Due fiscal year 2019

Due fiscal year 2020

Due fiscal year 2020

Due fiscal year 2023

Due fiscal year 2023

Due fiscal year 2025

Due fiscal year 2025

Due fiscal year 2027

Due fiscal year 2027

Due fiscal year 2028

Due fiscal year 2028

Due fiscal year 2030

Due fiscal year 2030

Due fiscal year 2036

Due fiscal year 2036

Due fiscal year 2041

Due fiscal year 2041

Due fiscal year 2044

Due fiscal year 2044

Common Shareholders' Equity

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Common stock, value

$525,932,000

$574,461,000

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Paid-in capital

11,847,000

10,710,000

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Retained Earnings

716,758,000

700,422,000

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Accumulated Other Comprehensive Income (Loss), Net of Tax

-7,961,000

-11,048,000

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Total Common shareholders' Equity

1,246,576,000

1,274,545,000

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Common shareholders equity, percentage of total capitalization

63.80%

69.80%

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Preferred Stock

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Preferred Stock

0

0

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Washington Gas Light Company preferred stock

28,173,000

28,173,000

15,000,000

15,000,000

7,173,000

7,173,000

6,000,000

6,000,000

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Preferred stock, percentage of total capitalization

1.40%

1.50%

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Long-Term Debt

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'

'

'

'

'

'

'

'

'

'

'

'

Medium Term Notes

691,000,000

583,000,000

'

'

'

'

'

'

0

67,000,000

20,000,000

20,000,000

25,000,000

25,000,000

50,000,000

50,000,000

50,000,000

50,000,000

20,000,000

20,000,000

40,500,000

40,500,000

125,000,000

125,000,000

52,000,000

52,000,000

8,500,000

8,500,000

50,000,000

50,000,000

75,000,000

75,000,000

175,000,000

0

Maximum Note Rate Range

'

'

'

'

'

'

'

'

5.17%

5.17%

4.83%

4.83%

5.17%

5.17%

7.46%

7.46%

4.76%

4.76%

6.65%

6.65%

5.44%

5.44%

6.82%

6.82%

6.85%

6.85%

7.50%

7.50%

5.78%

5.78%

5.21%

5.21%

5.00%

5.00%

Minimum Note Rate Range

'

'

'

'

'

'

'

'

4.88%

4.88%

4.83%

4.83%

5.17%

5.17%

7.46%

7.46%

4.76%

4.76%

6.65%

6.65%

5.44%

5.44%

6.40%

6.40%

6.57%

6.57%

7.50%

7.50%

5.70%

5.70%

5.21%

5.21%

4.22%

4.22%

Other long-term debt

8,350,000

8,097,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unamortized discount

-122,000

-30,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Less-current maturities

20,000,000

67,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Long-Term Debt

679,228,000

524,067,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Long Term Debt As Percentage Of Total Capitalization

34.80%

28.70%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Capitalization, Long-term Debt and Equity

$1,953,977,000

$1,826,785,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total Capitalization As Percentage

100.00%

100.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Consolidated_Statement_of_Capi1

Consolidated Statement of Capitalization - WGLH (Parenthetical) (USD $)	Sep. 30, 2014	Sep. 30, 2013
Preferred Stock [Member]	'	'
Preferred Stock [Abstract]	'	'
Preferred Stock, Shares Authorized	1,500,000	1,500,000
Preferred Stock, Par or Stated Value Per Share	$0	$0
Preferred Stock [Member] | WGL Holdings, Inc.	'	'
Preferred Stock [Abstract]	'	'
Preferred Stock, Shares Authorized	3,000,000	3,000,000
Preferred Stock, Issued	0	0
Preferred Stock, Par or Stated Value Per Share	$0	$0
Common Stock [Member] | WGL Holdings, Inc.	'	'
Common Shareholders' Equity	'	'
Common Stock, Par or Stated Value Per Share	$0	$0
Common Stock, Shares Authorized	120,000,000	120,000,000
Common Stock, Shares, Issued	50,656,553	51,774,204
Series One [Member] | WGL Holdings, Inc.	'	'
Preferred Stock [Abstract]	'	'
Preferred Stock, Shares Outstanding	150,000	150,000
Preferred Stock, Par or Stated Value Per Share	$4.80	$4.80
Series Two [Member] | WGL Holdings, Inc.	'	'
Preferred Stock [Abstract]	'	'
Preferred Stock, Shares Outstanding	70,600	70,600
Preferred Stock, Par or Stated Value Per Share	$4.25	$4.25
Series Three [Member] | WGL Holdings, Inc.	'	'
Preferred Stock [Abstract]	'	'
Preferred Stock, Shares Outstanding	60,000	60,000
Preferred Stock, Par or Stated Value Per Share	$5	$5

Consolidated_Statement_of_Capi2

Consolidated Statement of Capitalization - WGL (Washington Gas Light Company, USD $)

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Series One [Member]

Series One [Member]

Series Two [Member]

Series Two [Member]

Series Three [Member]

Series Three [Member]

Due fiscal year 2014

Due fiscal year 2014

Due fiscal year 2015

Due fiscal year 2015

Due fiscal year 2016

Due fiscal year 2016

Due fiscal year 2019

Due fiscal year 2019

Due fiscal year 2020

Due fiscal year 2020

Due fiscal year 2023

Due fiscal year 2023

Due fiscal year 2025

Due fiscal year 2025

Due fiscal year 2027

Due fiscal year 2027

Due fiscal year 2028

Due fiscal year 2028

Due fiscal year 2030

Due fiscal year 2030

Due fiscal year 2036

Due fiscal year 2036

Due fiscal year 2041

Due fiscal year 2041

Due fiscal year 2044

Due fiscal year 2044

Common Shareholders' Equity

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common stock, value

$46,479,000

$46,480,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Paid-in capital

480,620,000

477,968,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Retained Earnings

529,480,000

511,183,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Accumulated Other Comprehensive Income (Loss), Net of Tax

-6,413,000

-11,048,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total Common shareholders' Equity

1,050,166,000

1,024,583,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common Shareholders Equity As Percentage Of Total Capitalization

59.80%

65.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Preferred Stock

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Noncontrolling Interest, Amount Represented by Preferred Stock

28,173,000

28,173,000

15,000,000

15,000,000

7,173,000

7,173,000

6,000,000

6,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Preferred Stock As Percentage Of Total Capitalization

1.60%

1.80%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Long-Term Debt

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Medium Term Notes

691,000,000

583,000,000

'

'

'

'

'

'

0

67,000,000

20,000,000

20,000,000

25,000,000

25,000,000

50,000,000

50,000,000

50,000,000

50,000,000

20,000,000

20,000,000

40,500,000

40,500,000

125,000,000

125,000,000

52,000,000

52,000,000

8,500,000

8,500,000

50,000,000

50,000,000

75,000,000

75,000,000

175,000,000

0

Maximum Note Rate Range

'

'

'

'

'

'

'

'

0.00%

5.17%

4.83%

4.83%

5.17%

5.17%

7.46%

7.46%

4.76%

4.76%

6.65%

6.65%

5.44%

5.44%

6.82%

6.82%

6.85%

6.85%

7.50%

7.50%

5.78%

5.78%

5.21%

5.21%

5.00%

0.00%

Minimum Note Rate Range

'

'

'

'

'

'

'

'

0.00%

4.88%

4.83%

4.83%

5.17%

5.17%

7.46%

7.46%

4.76%

4.76%

6.65%

6.65%

5.44%

5.44%

6.40%

6.40%

6.57%

6.57%

7.50%

7.50%

5.70%

5.70%

5.21%

5.21%

4.22%

0.00%

Other Long-term Debt

8,350,000

8,097,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unamortized discount

-122,000

-30,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Less-current maturities

20,000,000

67,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Long-Term Debt

679,228,000

524,067,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Long term debt, percentage of total capitalization

38.60%

33.20%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Capitalization, Long-term Debt and Equity

$1,757,567,000

$1,576,823,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total capitalization, percentage

100.00%

100.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Consolidated_Statement_of_Capi3

Consolidated Statement of Capitalization - WGL (Parenthetical) (USD $)	Sep. 30, 2014	Sep. 30, 2013
Washington Gas Light Company	'	'
Common Shareholders' Equity	'	'
Common Stock, Par or Stated Value Per Share	$1	$1
Common Stock, Shares Authorized	80,000,000	80,000,000
Common Stock, Shares, Issued	46,479,536	46,479,536
Preferred Stock [Abstract]	'	'
Preferred Stock, Shares Authorized	1,500,000	1,500,000
Preferred Stock [Member]	'	'
Preferred Stock [Abstract]	'	'
Preferred Stock, Shares Authorized	1,500,000	1,500,000
Preferred Stock, Par or Stated Value Per Share	$0	$0
Series One [Member] | Washington Gas Light Company	'	'
Preferred Stock [Abstract]	'	'
Preferred Stock, Shares Outstanding	150,000	150,000
Preferred Stock, Par or Stated Value Per Share	$4.80	$4.80
Series Two [Member] | Washington Gas Light Company	'	'
Preferred Stock [Abstract]	'	'
Preferred Stock, Shares Outstanding	70,600	70,600
Preferred Stock, Par or Stated Value Per Share	$4.25	$4.25
Series Three [Member] | Washington Gas Light Company	'	'
Preferred Stock [Abstract]	'	'
Preferred Stock, Shares Outstanding	60,000	60,000
Preferred Stock, Par or Stated Value Per Share	$5	$5

Consolidated_Statements_of_Com1

Consolidated Statements of Common Shareholders Equity - WGLH (WGL Holdings, Inc., USD $)	WGL Holdings, Inc.	Common Stock [Member]	Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss, Net of Taxes
In Thousands, except Share data, unless otherwise specified	USD ($)	WGL Holdings, Inc.	WGL Holdings, Inc.	WGL Holdings, Inc.	WGL Holdings, Inc.
		USD ($)	USD ($)	USD ($)	USD ($)
Common shareholders' equity, beginning balance at Sep. 30, 2011	$1,202,715	$557,594	$7,731	$648,052	($10,662)
Beginning Balance, shares at Sep. 30, 2011	'	51,365,337	'	'	'
Net Income	141,138	'	'	141,138	'
OTHER COMPREHENSIVE INCOME (LOSS)	-1,539	'	'	'	-1,539
Dividend Reinvestment	6,317	6,317	'	'	'
Dividend Reinvestment, Shares	'	152,435	'	'	'
Repurchase of common stock	0	'	'	'	'
Stock-based compensation	4,088	3,687	401	'	'
Stock-based compensation, Shares	'	93,875	'	'	'
Dividends Abstract	'	'	'	'	'
Common Stock	-81,843	'	'	-81,843	'
Preferred Stock	-1,320	'	'	-1,320	'
Common shareholders' equity, ending balance at Sep. 30, 2012	1,269,556	567,598	8,132	706,027	-12,201
Ending Balance, shares at Sep. 30, 2012	'	51,611,647	'	'	'
Net Income	81,573	'	'	81,573	'
OTHER COMPREHENSIVE INCOME (LOSS)	1,153	'	'	'	1,153
Dividend Reinvestment	6,254	6,254	'	'	'
Dividend Reinvestment, Shares	'	145,920	'	'	'
Repurchase of common stock	0	'	'	'	'
Stock-based compensation	3,187	609	2,578	'	'
Stock-based compensation, Shares	'	16,637	'	'	'
Dividends Abstract	'	'	'	'	'
Common Stock	-85,858	'	'	-85,858	'
Preferred Stock	-1,320	'	'	-1,320	'
Common shareholders' equity, ending balance at Sep. 30, 2013	1,274,545	574,461	10,710	700,422	-11,048
Ending Balance, shares at Sep. 30, 2013	'	51,774,204	'	'	'
Net Income	107,260	'	'	107,260	'
OTHER COMPREHENSIVE INCOME (LOSS)	3,087	'	'	'	3,087
Dividend Reinvestment	4,649	4,649	'	'	'
Dividend Reinvestment, Shares	'	114,883	'	'	'
Repurchase of common stock	-56,136	-56,136	'	'	'
Repurchase of common stock, Shares	'	-1,304,504	'	'	'
Stock-based compensation	4,095	2,958	1,137	'	'
Stock-based compensation, Shares	'	71,970	'	'	'
Dividends Abstract	'	'	'	'	'
Common Stock	-89,604	'	'	-89,604	'
Preferred Stock	-1,320	'	'	-1,320	'
Common shareholders' equity, ending balance at Sep. 30, 2014	$1,246,576	$525,932	$11,847	$716,758	($7,961)
Ending Balance, shares at Sep. 30, 2014	'	50,656,553	'	'	'

Consolidated_Statements_of_Com2

Consolidated Statements of Common Shareholders Equity (Parenthetical) - WGLH (WGL Holdings, Inc., USD $)	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
WGL Holdings, Inc.	'	'	'
DIVIDENDS DECLARED PER COMMON SHARE	$1.74	$1.66	$1.59

Consolidated_Statements_of_Com3

Consolidated Statements of Common Shareholders Equity - WGL (Washington Gas Light Company, USD $)		Washington Gas Light Company	Common Stock [Member]	Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss, Net of Taxes
In Thousands, except Share data, unless otherwise specified		USD ($)	Washington Gas Light Company	Washington Gas Light Company	Washington Gas Light Company	Washington Gas Light Company
			USD ($)	USD ($)	USD ($)	USD ($)
Common shareholders' equity, beginning balance at Sep. 30, 2011		$990,135	$46,479	$473,099	$481,219	($10,662)
Beginning Balance, shares at Sep. 30, 2011		'	46,479,536	'	'	'
Net Income		110,046	'	'	110,046	'
OTHER COMPREHENSIVE INCOME (LOSS)		-1,539	'	'	'	-1,539
Stock-based compensation	[1]	2,535	'	2,535	'	'
Dividends declared:		'	'	'	'	'
Common Stock		-74,114	'	'	-74,114	'
Preferred Stock		-1,320	'	'	-1,320	'
Common shareholders' equity, ending balance at Sep. 30, 2012		1,025,743	46,479	475,634	515,831	-12,201
Ending Balance, shares at Sep. 30, 2012		'	46,479,536	'	'	'
Net Income		72,322	'	'	72,322	'
OTHER COMPREHENSIVE INCOME (LOSS)		1,153	'	'	'	1,153
Stock-based compensation	[1]	2,334	'	2,334	'	'
Dividends declared:		'	'	'	'	'
Common Stock		-75,649	'	'	-75,649	'
Preferred Stock		-1,320	'	'	-1,320	'
Common shareholders' equity, ending balance at Sep. 30, 2013		1,024,583	46,479	477,968	511,184	-11,048
Ending Balance, shares at Sep. 30, 2013		'	46,479,536	'	'	'
Net Income		98,324	'	'	98,324	'
OTHER COMPREHENSIVE INCOME (LOSS)		4,635	'	'	'	4,635
Stock-based compensation	[1]	2,652	'	2,652	'	'
Dividends declared:		'	'	'	'	'
Common Stock		-78,708	'	'	-78,708	'
Preferred Stock		-1,320	'	'	-1,320	'
Common shareholders' equity, ending balance at Sep. 30, 2014		$1,050,166	$46,479	$480,620	$529,480	($6,413)
Ending Balance, shares at Sep. 30, 2014		'	46,479,536	'	'	'
[1]	Stock-based compensation is based on the stock awards of WGL Holdings that are allocated to Washington Gas Light Company for its pro-rata share.

Accounting_Policies

Accounting Policies	12 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Organization Consolidation And Presentation Of Financial Statements Disclosure Text Block	'
	NOTE 1. ACCOUNTING POLICIES
	GENERAL
	WGL Holdings, Inc. (WGL) is a holding company that owns all of the shares of common stock of Washington Gas Light Company (Washington Gas), a regulated natural gas utility, and all of the shares of common stock of Washington Gas Resources Corporation (Washington Gas Resources), Hampshire Gas Company (Hampshire) and Crab Run Gas Company. Washington Gas Resources owns all of the shares of common stock of four non-utility subsidiaries that include Washington Gas Energy Services, Inc. (WGEServices), Washington Gas Energy Systems, Inc. (WGESystems), WGL Midstream and WGSW, Inc. (WGSW). Except where the content clearly indicates otherwise, “WGL,” “we,” “us” or “our” refers to the holding company or the consolidated entity of WGL Holdings, Inc. and all of its subsidiaries. Unless otherwise noted, these notes apply equally to WGL and Washington Gas.
	NATURE OF OPERATIONS
	Washington Gas and Hampshire comprise our regulated utility segment. 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 78.1% of the total therms delivered to customers by Washington Gas in fiscal year September 30, 2014. Deliveries to interruptible customers accounted for 14.3% and deliveries to customers who use natural gas to generate electricity accounted for 7.6%. These amounts do not include deliveries related to Washington Gas' asset optimization program discussed below. Hampshire 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 Federal Energy Regulatory Commission (FERC).
	The retail energy-marketing segment consists of WGEServices which competes with regulated utilities and other unregulated third party marketers to sell natural gas and electricity directly to residential, commercial, industrial and governmental customers with the objective of earning a profit through competitive pricing. The commodities that WGEServices sells are delivered to retail customers through assets owned by regulated utilities. Washington Gas delivers the majority of natural gas sold by WGEServices, and unaffiliated electric utilities deliver all of the electricity sold. WGEServices owned multiple solar PV distributed generation assets at September 30, 2014, though the results from these activities are presented in the commercial energy systems segment. Other than these facilities, WGEServices does not own or operate any other natural gas or electric generation, production, transmission or distribution assets. At September 30, 2014, WGEServices served approximately 157,000 natural gas customers and approximately 162,000 electricity customers located in Maryland, Virginia, Delaware, Pennsylvania and the District of Columbia.
	The commercial energy systems segment consists of WGESystems, WGSW and the results of operations of affiliate owned commercial distributed energy projects. This segment focuses on clean and energy efficient solutions for its customers, driving earnings through (i) upgrading the mechanical, electrical, water and energy-related infrastructure of large governmental and commercial facilities by implementing both traditional as well as alternative energy technologies; (ii) owning and operating distributed generation assets such as solar PV systems, combined heat and power plants, and natural gas fuel cells and (iii) passive investments in residential and commercial retail solar PV companies. This segment has activities in 15 different states and the District of Columbia, but is concentrated in the mid-Atlantic and northeast regions.
	The midstream energy services segment, which consists of the operations of WGL Midstream, engages in investing in and optimizing natural gas pipelines and storage facilities in the Midwest and Eastern United States. WGL Midstream enters into both physical and financial transactions in a manner intended to utilize the most effective energy risk management products available to mitigate risks while maximizing potential profits from the optimization of these assets under its management.
	Refer to Note 16—Operating Segment Reporting for further discussion of our segments.
	CONSOLIDATION OF FINANCIAL STATEMENTS
	The consolidated financial statements include the accounts of WGL and its subsidiaries during the fiscal years reported. Certain prior period amounts have been recast to conform to current period presentation. Inter-company transactions have been eliminated. Refer to Note 18—Related Party Transactions for a discussion of inter-company transactions. WGL has a variable interest in five investments that qualify as variable interest entities (VIEs). At September 30, 2014, WGL and its subsidiaries are not the primary beneficiary for any of the VIEs, therefore we have not consolidated any of the VIE entities. Our other investment projects are recorded using the cost method and as direct financing leases. Refer to Note 17—Other Investments for a discussion of VIEs and other investments.
	USE OF ESTIMATES IN THE PREPARATION OF FINANCIAL STATEMENTS
	In accordance with generally accepted accounting principles in the United States of America (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. Washington Gas capitalizes AFUDC as a component of construction overhead. The before-tax rates for AFUDC for fiscal years September 30, 2014, 2013 and 2012 were 3.36%, 5.43% and 7.40%, respectively.
	Washington Gas charges maintenance and repairs directly to operating expenses, except those charges applicable to transportation and power-operated equipment, which it allocates to operating expenses, construction and other accounts based on the use of the equipment. 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 depreciation and amortization rate of the regulated utility segment was 2.77%, 2.86% and 2.87% during fiscal years 2014, 2013 and 2012, 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 Obligatons".
	At September 30, 2014 and 2013, 93.6% and 95.6%, respectively, of WGL's consolidated original cost of property, plant and equipment was related to the regulated utility segment as shown below.
	Property, Plant and Equipment at Original Cost
	September 30,		2014			2013
	($ In millions)		Dollars	%		Dollars	%
	Regulated utility segment
	Distribution, transmission and storage	$	3,635.30	79.3	$	3,356.10	81.5
	General, miscellaneous and intangibles		448.3	9.8		430.6	10.4
	Construction work in progress (CWIP)		203.9	4.5		150.8	3.7
	Total regulated utility segment		4,287.50	93.6		3,937.50	95.6
	Unregulated segments		295.3	6.4		180.6	4.4
	Total	$	4,582.80	100	$	4,118.10	100
	IMPAIRMENT OF LONG-LIVED ASSETS
	Management regularly reviews property and equipment and other long-lived assets, including certain definite-lived intangible assets and our equity method investments for possible impairment. This review occurs quarterly, or more frequently if events or changes in circumstances indicate the carrying amount of the asset may not be recoverable.
	During September 30, 2014, 2013 and 2012, Washington Gas recorded impairment charges of $0.8 million, $2.6 million and $5.0 million, respectively, in operation and maintenance expense related to its Springfield Operations Center asset. Washington Gas is actively marketing the unused operations facility for sale. At September 30, 2014 and 2013, Washington Gas recorded a $1.9 million and $0.5 million impairment loss for the unrecoverable portion of the costs incurred associated with an abandoned LNG storage project.
	For our equity and cost method investments, an impairment is recorded when the investment has experienced decline in value that is other-than-temporary. Additionally, if the projects in which we hold an investment recognize an impairment loss, we would record our proportionate share of that impairment loss and evaluate the investment for decline in value that is other-than-temporary. There were no events or circumstances during the years ended September 30, 2014, 2013 and 2012 that resulted in any impairment charges.
	OPERATING LEASES
	We have classified the lease of our corporate headquarters as an operating lease. 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 lease. For this purpose, the lease term began on the date when the lessor commenced constructing the leasehold improvements which allowed us to occupy our corporate headquarters. 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 15-year non-cancelable period of the lease. Refer to Note 13—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. We did not have any restrictions on our cash balances that would impact the payment of dividends by WGL or our subsidiaries as of September 30, 2014 and 2013.
	REVENUE AND COST RECOGNITION
	Regulated Utility Operations
	Revenues.  For regulated deliveries of natural gas, Washington Gas reads meters and bills customers on a 21 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.
	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. Refer to Note 16—Operating Segment Reporting for amounts recorded related to revenue taxes.
	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 WGEServices, into a single “net” adjustment to the regulatory asset or liability. Refer to Note 18—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 shareholders.
	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 or, in the case of amounts to be shared with rate payers, regulatory liabilities.
	Non-Utility Operations
	Retail Energy-Marketing Segment.  WGEServices sells natural gas and electricity on an unregulated basis to residential, commercial and industrial customers both inside and outside the Washington Gas service territory.
	WGEServices enters into indexed or fixed-rate contracts with residential, commercial and industrial customers for sales of natural gas and electricity. Customer contracts, which typically have terms less than 24 months, but may extend up to five years, allow WGEServices to bill customers based upon metered gas and electricity usage. Usage is measured either on a cycle basis at customer premises or based on quantities delivered to the local utility, both of which may vary by month. The billing cycles for customers do not coincide with the accounting periods used for financial reporting purposes; therefore, WGEServices accrues unbilled revenues for gas and electricity delivered, but not yet billed, at the end of each accounting period. Revenues are reflected in “Operating Revenues—Non utility.”
	WGEServices procures natural gas and electricity supply under contract structures in which it assembles the various components of supply from multiple suppliers to match its customer requirements. The cost of natural gas and electricity for these purchases is recorded using the contracted volumes and prices in “Non-Utility cost of energy-related sales.”
	Commercial Energy Systems Segment.  WGESystems recognizes income and expenses for all design-build construction contracts using the percentage-of-completion method in “Operating Revenues—Non-utility” and “Non-Utility cost of energy-related sales.” WGESystems also recognizes income from its distributed energy assets based on the terms of the related power purchase agreements. Solar Renewable Energy Certificates (SRECs) are recorded as inventory by WGESystems after every 1,000 Kilowatt-hours (kwh) of electricity are produced by an eligible solar facility. WGESystems recognizes income on the sale of SRECs based on the contractual terms and conditions of the sale. WGSW recognizes income on its investments in distributed energy assets based on the specific terms of its sale leaseback arrangements and through the hypothetical liquidation at book value approach to the equity method of investment accounting for its investment interest. Other income and expense is recognized from the lease of distributed energy assets associated with the SunEdison and Nextility associations.
	Midstream Energy Services Segment.  WGL Midstream reports its margins in non-utility revenue by netting its cost / loss on physical and financial gas purchase contracts with revenues / gains on physical and financial gas sales contracts.
	Other Activities. Washington Gas Resources recognizes income on its investment using the cost approach of investment accounting. Crab Run recognizes income using the equity method of accounting.
	STORAGE GAS VALUATION METHODS
	For Washington Gas and WGEServices, storage gas inventory is stated at the lower-of-cost or market as determined using the first-in, first-out method. For WGL Midstream, storage gas inventory is stated at the lower-of-cost or market using the weighted average cost method.
	For the fiscal year ended September 30, 2014, Washington Gas recorded a decrease to net income due to a lower-of-cost or market adjustment of $0.2 million. For the fiscal year ended September 30, 2013, Washington Gas did not record any lower-of-cost or market adjustments. For the fiscal year ended September 30, 2012, Washington Gas recorded a decrease to net income due to a lower-of-cost or market adjustment of $1.4 million. For the fiscal years ended September 30, 2014, 2013 and 2012, WGEServices did not record any lower-of-cost or market adjustments. For the fiscal years ended September 30, 2014, 2013 and 2012, WGL Midstream recorded a decrease to net income due to lower-of-cost or market adjustments of $3.0 million, $10.1 million and $22.4 million, respectively.
	RATE REFUNDS DUE TO CUSTOMERS
	When Washington Gas files a request with certain regulatory commissions to modify customers' rates, it is 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 13—Commitments and Contingencies for further discussion of regulatory matters and related contingencies.
	WEATHER-RELATED INSTRUMENTS
	Periodically, we purchase certain weather-related instruments, such as HDD derivatives and CDD derivatives. We account for these weather related instruments in accordance with Financial Accounting Standards Board Accounting Standards Codification (ASC) Subtopic 815-45, Derivatives and Hedging—Weather Derivatives. For weather insurance policies and HDD derivatives, benefits or costs are ultimately recognized to the extent actual HDDs fall above or below the contractual HDDs for each instrument. Benefits or costs are recognized for CDD derivatives when the average temperature exceeds a contractually stated level during the contract period. Premiums for weather-related instruments are amortized based on the pattern of normal temperature days over the coverage period. Weather-related instruments for which we collect a premium are carried at fair value. Washington Gas' weather related instrument premium expense or benefit is not considered in establishing retail rates. Washington Gas does not purchase such instruments for jurisdictions in which it has received rate mechanisms that compensate it on a normal weather basis. Refer to Note 14—Derivative and Weather-Related Instruments for further discussion of our weather-related instruments.
	DERIVATIVE ACTIVITIES
	Regulated Utility. 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 recoverable or refundable to customers and therefore subject to ASC Topic 980, Regulated Operations, 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 locking in operating margins that Washington Gas expects to ultimately realize. The 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 volatility will not change the margins that Washington Gas expects to realize from these transactions. 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 Medium-Term Notes (MTNs). 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 14—Derivative and Weather-Related Instruments for further discussion of our derivative activities.
	Non-Utility Operations. WGEServices enters into both physical and financial contracts for the purchase and sale of natural gas and electricity. We designate a portion of these physical contracts related to the purchase of natural gas and electricity to serve our customers as “normal purchases and normal sales;” therefore, they are not subject to the mark-to-market accounting requirements of ASC Topic 815. WGL Midstream enters into derivative contracts for the purpose of optimizing its storage and transportation capacity as well as managing the transportation and storage assets on behalf of third parties. The financial contracts and the portion of the physical contracts that qualify as derivative instruments and are subject to the mark-to-market accounting requirements are recorded on the balance sheet at fair value and are reflected in earnings. WGEServices records these derivatives as revenues or expenses depending on the nature of the economically hedged item. WGL Midstream nets financial and physical contracts in revenues. WGL may, from time to time, designate interest rate swaps used to manage the interest rate risk associated with future debt issuances, as cash flow hedges. Any gains or losses arising from the effective portion of cash flow hedges are recorded in other comprehensive income and are amortized using the effective interest rate method into earnings over the same period as the hedged interest payments are made.  Gains or losses arising from the ineffective portion of cash flow hedges are recognized in earnings immediately.
	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, including those where regulators prohibit deferred income tax treatment 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. Refer to Note 2— Regulated Operations for Washington Gas' regulatory assets and liabilities associated with income taxes due from and to customers at September 30, 2014 and 2013. Amounts applicable to income taxes due from and due to customers primarily represent differences between the book and tax basis of net utility plant in service. We amortize investment tax credits as reductions to income tax expense over the estimated service lives of the related properties. Refer to Note 9—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, which requires us to measure and recognize stock-based compensation expense in our financial statements based on the fair value at the date of grant for our equity-classified share-based awards, which include performance shares and stock options granted to certain employees and shares issued to directors. For liability-classified share-based awards, which include performance units, we recognize stock-based compensation expense based on their fair value at the end of each reporting period. For both equity-classified and liability-classified share-based awards, 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 11—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 asset retirement obligations include the costs to cut, purge and cap distribution system, remove asbestos 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.
	WGL Holdings, Inc.
	Changes in Asset Retirement Obligations
			September 30,
	(In millions)		2014		2013
	Asset retirement obligations at beginning of year	$	104	$	72.7
	Liabilities incurred in the period		4.9		1.2
	Liabilities settled in the period		-5.2		-1
	Accretion expense		4.4		3.3
	Revisions in estimated cash flows(a)		73.1		27.8
	Asset retirement obligations at the end of the year(b)	$	181.2	$	104
	Washington Gas Light Company
	Changes in Asset Retirement Obligations
			September 30,
	(In millions)		2014		2013
	Asset retirement obligations at beginning of year	$	102.7	$	71.5
	Liabilities incurred in the period		4.9		1.1
	Liabilities settled in the period		-5.2		-1
	Accretion expense		4.3		3.3
	Revisions in estimated cash flows(a)		73.1		27.8
	Asset retirement obligations at the end of the year(b)	$	179.8	$	102.7
	(a) WGL revised its assumptions regarding the timing and amounts related to its obligation to cut, cap and purge pipeline. The revision is primarily driven by our accelerated pipeline replacement programs.
	(b) Includes short-term asset retirement obligations of $6.0 million and $2.7 million for fiscal year 2014 and 2013, respectively.
ACCOUNTING STANDARDS ADOPTED IN FISCAL YEAR 2014
Standard
Description
Date of adoption
Effect on the financial statements or other significant matters
ASU 2011-11, Disclosures about Offsetting Assets and Liabilities (Topic 210)
The standard amends the existing disclosure requirements on offsetting by requiring enhanced disclosures about financial instruments and derivative instruments that are either: (i) offset in accordance with existing guidance or (ii) subject to an enforceable master netting arrangement or similar agreement, irrespective of whether they are offset on the balance sheet
1-Oct-13
As a result of the standards, additional disclosures regarding master netting arrangements were added to Note 14 - Derivative and Weather-Related Instruments. The adoption of these standards did not otherwise affect our financial statements.
ASU 2013-01, Clarifying the Scope of the Disclosures about Offsetting Assets and Liabilities (Topic 210)
The standard limits the scope of the required disclosures to derivatives, repurchase agreements and securities borrowing and securities lending transactions. The disclosures are required irrespective of whether the transactions are offset in the statement of financial position.
ASU 2013-02, Comprehensive Income (Topic 220): Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income
The standard requires entities to (i) present information about reclassification adjustments from accumulated other comprehensive income (AOCI) to net income in their entirety – the effect on the reclassification on each affected net income line item and (ii) for AOCI reclassification items that are not reclassified in their entirety into net income – a cross-reference to other required US GAAP disclosures. The reclassification information may be presented in a single note or on the face of the financial statements.
1-Oct-13
We have presented information about reclassification adjustments out of accumulated other comprehensive income in a footnote to the financial statements. Refer to Note 19 – Changes in Accumulated Other Comprehensive Income for the details of this disclosure. The adoption of this standard did not otherwise affect our financial statements.
OTHER NEWLY ISSUED ACCOUNTING STANDARDS
Effect on the financial statements or other significant matters
ASU 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists (Topic 740)
The standard amends the existing disclosure requirement by requiring an unrecognized tax benefit, or a portion of an unrecognized tax benefit to be presented in the financial statements as a reduction to a deferred tax asset in most circumstances.
1-Oct-14
We do not expect the adoption of this standard to have a material effect on our financial statements.
ASU 2014-09, Revenue from Contracts with Customers (Topic 606)
The standard 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.
1-Oct-17
We are in the process of evaluating the impact the adoption of this standard will have on our financial statements.
ASU 2014-10, Development Stage Entities (Topic 915)
The standard amends the existing disclosure requirement by eliminating certain disclosure requirements relating to those entities. The update also removes certain guidance on evaluating whether a development stage entity has sufficient equity at risk as a criteria used in determining whether an entity is a variable interest entity.
1-Oct-16
We do not expect the adoption of this standard to have a material effect on our financial statements.
ASU 2014-15, Presentation of Financial Statements - Going Concern (Topic 205)
The standard amends the existing disclosure requirement providing guidance about management's responsibility to evaluate whether there is substantial doubt about the entity's ability to continue as a going concern and to provide related footnote disclosures. The new guidance requires that management perform a going concern analysis as of the date that the financial statements are issued and for the analysis to cover the year following the issuance date.
1-Oct-17
We do not expect adoption of this standard to have a material effect on our financial statements.
Standard
Description
Date of adoption

Regulated_Operations

Regulated Operations	12 Months Ended
	Sep. 30, 2014
Regulated Operations [Abstract]	'
Public Utilities Disclosure	'
	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 amounts previously collected from customers and for future outflows that are expected to be incurred in the future (regulatory liabilities).
	At September 30, 2014 and 2013, we recorded the following regulatory assets and liabilities on our balance sheets. These assets and liabilities will be recognized as expenses or revenues in future periods as they are reflected in customers' rates.
	Regulatory Assets and Liabilities
			Regulatory				Regulatory
	(In millions)		Assets				Liabilities
	September 30,		2014		2013		2014		2013
	Current:
	Gas costs due from/to customers(a)	$	-	$	-	$	16.2	$	23.4
	Interruptible sharing(a)		3.4		10.7		-		1.9
	Revenue normalization mechanisms for Maryland and Virginia(a)		-		0.1		5.5		1.5
	Plant recovery mechanisms		0.4		-		0.9		0.2
	Total current	$	3.8	$	10.8	$	22.6	$	27
	Deferred:
	Accrued asset removal costs	$	-	$	-	$	327.4	$	321.3
	Deferred gas costs(a)		191.3		94		-		-
	Pension and other post-retirement benefits
	Other post-retirement benefit costs—trackers(b)		-		0.7		-		-
	Deferred pension costs/income—trackers(b)		45.1		51		-		-
	ASC Topic 715 unrecognized costs/income(a)(c)
	Pensions		147.9		155.1		-		-
	Other post-retirement benefits		-		33.8		86.4		-
	Total pension and other post-retirement benefits		193		240.6		86.4		-
	Other
	Income tax-related amounts due from/to customers(d)		30.4		24.9		4.8		4.5
	Losses/gains on issuance and extinguishments of
	debt and interest-rate derivative instruments(a)(e)		12		11.6		1.7		0.6
	Deferred gain on sale of assets(a)		-		-		1.4		1.7
	Rights-of-way fees(a)		1.5		-		-		1.6
	Other costs—Business process outsourcing (a)		1		1.4		-		-
	Nonretirement postemployment benefits(a)(f)		16.3		15.4		-		-
	Deferred integrity management expenditures(a)(g)		2.7		-		-		-
	Recoverable portion of abandoned LNG facility(a)		5.6		7.9		-		-
	Other regulatory expenses(a)		2.1		4.8		9.7		5.1
	Total other	$	71.6	$	66	$	17.6	$	13.5
	Total deferred	$	455.9	$	400.6	$	431.4	$	334.8
	Total	$	459.7	$	411.4	$	454	$	361.8
	(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) Relates to the District of Columbia jurisdiction.
	(c) Refer to Note 10-Pension and Other Post-Retirement Benefit Plans for a further discussion of these amounts.
	(d) 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.
	(e) 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.
	(f) 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.
	(g)This balance represents amounts for deferred expenditures associated with Washington Gas' Distribution Integrity Management Program (DIMP) in Virginia.
	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, and the recovery of our regulatory assets at September 30, 2014 is probable. Refer to Note 13—Commitments and Contingencies for further discussion of our regulated operations.

Accounts_Payable_and_Other_Acc

Accounts Payable and Other Accrued Liabilities	12 Months Ended
	Sep. 30, 2014
Accounts Payable and Other Accrued Liabilities [Abstract]	'
Accounts Payable and Other Accrued Liabilities	'
	NOTE 3. ACCOUNTS PAYABLE AND OTHER ACCRUED LIABILITIES
	The tables below provide details for the amounts included in “Accounts payable and other accrued liabilities” on the balance sheets for both WGL and Washington Gas.
		WGL Holdings, Inc.
				September 30,
		(In millions)		2014		2013
		Accounts payable—trade	$	278.8	$	216.3
		Employee benefits and payroll accruals		19.8		23.4
		Embedded derivatives and other accrued liabilities		14.6		30.9
		Total	$	313.2	$	270.6
		Washington Gas Light Company
				September 30,
		(In millions)		2014		2013
		Accounts payable—trade	$	146.4	$	99.7
		Employee benefits and payroll accruals		18.2		21.4
		Embedded derivatives and other accrued liabilities		11.9		11.7
		Total	$	176.5	$	132.8

ShortTerm_Debt

Short-Term Debt	12 Months Ended
	Sep. 30, 2014
Short-Term Debt [Abstract]	'
Short-Term Debt	'
	NOTE 4. SHORT-TERM DEBT
	WGL and Washington Gas satisfy their short-term financing requirements through the sale of commercial paper or through bank borrowings. Due to the seasonal nature of the regulated utility and retail energy-marketing segments, 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. WGL's policy 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 September 30, 2014 and 2013.
	Committed Credit Available (In millions)
	30-Sep-14	WGL Holdings, Inc.(b)		Washington Gas		Total Consolidated
	Committed credit agreements
	Unsecured revolving credit facility, expires April 3, 2017(a)	$	450	$	350	$	800
	Less: Commercial Paper		-364.5		-89		-453.5
	Net committed credit available	$	85.5	$	261	$	346.5
	Weighted average interest rate		0.20%		0.13%		0.19%
	30-Sep-13
	Committed credit agreements
	Unsecured revolving credit facility, expires April 3, 2017(a)	$	450	$	350	$	800
	Less: Commercial Paper		-248.6		-124.5		-373.1
	Net committed credit available	$	201.4	$	225.5	$	426.9
	Weighted average interest rate		0.21%		0.13%		0.19%
	(a)Both WGL and Washington Gas have the right to request extensions with the banks’ approval. WGL’s revolving credit facility permits it to borrow an additional $100 million, with the banks’ approval, for a total of $550 million. Washington Gas’ revolving credit facility permits it to borrow an additional $100 million, with the banks’ approval, for a total of $450 million.
	(b)WGL Holdings includes all subsidiaries other than Washington Gas Light Company.
	At September 30, 2014 and 2013, there were no outstanding bank loans from WGL's or Washington Gas' revolving credit facilities.
	Under the terms of the credit agreements, the ratio of consolidated financial indebtedness to consolidated total capitalization may not exceed 0.65 to 1.0 (65%). In addition, WGL and Washington Gas are 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 if WGL or Washington Gas 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 September 30, 2014, WGL and Washington Gas were in compliance with all of the covenants under their revolving credit facilities.

LongTerm_Debt

Long-Term Debt	12 Months Ended
	Sep. 30, 2014
Long-Term Debt [Abstract]	'
Long-Term Debt	'
	NOTE 5. 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. Washington Gas had no debt outstanding under the Mortgage at September 30, 2014 and 2013. Any FMBs that may be issued in the future will represent indebtedness of Washington Gas.
	SHELF REGISTRATION
	On August 18, 2014, WGL entered into an Indenture with The Bank of New York Mellon (the "Trustee") to issue an unlimited amount of debt securities. Supplemental indentures will supplement the Indenture and establish the respective terms of the notes. The offering of the notes has been registered under a shelf registration statement on Form S-3.
	At September 30, 2014, Washington Gas had the capacity under a shelf registration to issue up to $275.0 million of additional MTNs.
	UNSECURED NOTES
	Washington Gas issues unsecured MTNs 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. At September 30, 2014 and 2013, outstanding MTNs and private placement notes were $691.0 million and $583.0 million, respectively, at a weighted average interest rate of 5.65% and 5.91%, respectively.
	The indenture for the unsecured MTNs and the note purchase agreement for the private placement notes provide that Washington Gas will not issue any FMBs under its Mortgage without securing all MTNs and the subject private placement notes with the Mortgage.
	Certain of Washington Gas' outstanding MTNs and private placement notes have a make-whole call feature that pays the holder a premium based on a spread over the yield to maturity of a U.S. Treasury security having a comparable maturity, when that particular note is called by Washington Gas before its stated maturity date. With the exception of this make-whole call feature, Washington Gas is not required to pay call premiums for calling debt prior to the stated maturity date.
	The table below shows MTN and private placement issuances and retirements for the year ended September 30, 2014.
		MTN and Private Placement Issuances and Retirements
		($ In millions)	Principal			Interest Rate	Nominal Maturity Date
		Year Ended September 30, 2014
		Issuances:
		12/5/13	$	75		5.00%(a)	12/15/43
		9/12/14		100		4.22%(b)	9/15/44
		Total	$	175
		Retirements:
		11/7/13	$	37		4.88%	11/7/13
		9/10/14		30		5.17%	9/10/14
		Total	$	67
		(a)The estimated effective cost of the issued notes, including consideration of issuances fees and hedge costs, is 4.95%.
		(b)The estimated effective cost of the issued notes, including consideration of issuances fees and hedge costs, is 4.27%.
	There were no MTN or private placement issuances or retirements for the year ended September 30, 2013.
	LONG-TERM DEBT MATURITIES
	Maturities of long-term debt for each of the next five fiscal years and thereafter as of September 30, 2014 are summarized in the following table.
		Long-Term Debt Maturities(a)
		(In millions)	MTNs		Other		Total
		2015	$	20	$	-	$	20
		2016		25		-		25
		2017		-		-		-
		2018		-		-		-
		2019		50		-		50
		Thereafter		596		-		596
		Total (before project debt financing)	$	691	$	-	$	691
		Project debt financing(b)		-		8.3		8.3
		Total	$	691	$	8.3	$	699.3
		Less: current maturities		20		-		20
		Total non-current	$	671	$	8.3	$	679.3
		(a)Excludes unamortized discounts of $121,567 at September 30, 2014.
		(b)Project debt financing is anticipated to be a non-cash extinguishment. Refer to Note 13 - Commitments and Contingencies for further discussion of this construction project financing.

Common_Stock

Common Stock	12 Months Ended
	Sep. 30, 2014
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]	'
Common Stock	'
	NOTE 6. COMMON STOCK — WGL
	COMMON STOCK OUTSTANDING
	Shares of common stock outstanding were 50,656,553 and 51,774,204 at September 30, 2014 and 2013, respectively.
	COMMON STOCK RESERVES
	At September 30, 2014, there were 4,582,301 authorized, but unissued, shares of common stock reserved under the following plans:
	Common Stock Reserves
	Reserve for:	Number of Shares
	Omnibus incentive compensation plan(a)	999,443
	Dividend reinvestment and common stock purchase plan	2,849,012
	Employee savings plans	637,196
	Directors’ stock compensation plan	96,650
	Total common stock reserves	4,582,301
	(a)In March 2007, WGL adopted a shareholder-approved Omnibus Incentive Compensation Plan to replace on a prospective basis the 1999 Incentive Compensation Plan. Included are shares that may be issued which would reduce the number of shares authorized under the Omnibus Incentive Compensation Plan. These shares include 301,378 shares dedicated to performance shares granted but not vested and include 5,318 shares dedicated to stock options issued but not exercised. Refer to Note 11 - Stock-Based Compensation for a discussion regarding our stock-based compensation plans.

Preferred_Stock

Preferred Stock	12 Months Ended
	Sep. 30, 2014
Preferred Stock [Abstract]	'
Preferred Stock	'
	NOTE 7. 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. 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

Earnings_Per_Share

Earnings Per Share	12 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Earnings Per Share	'
	NOTE 8. EARNINGS PER SHARE
	Basic EPS is computed by dividing net income by the weighted average number of common shares outstanding during the reported period. Diluted EPS assumes the issuance of common shares pursuant to stock-based compensation plans at the beginning of the applicable period unless the effect of such issuance would be anti-dilutive (refer to Note 11—Stock-Based Compensation). The following table reflects the computation of our basic and diluted EPS for the fiscal years ended September 30, 2014, 2013 and 2012.
	Basic and Diluted EPS
		Years Ended September 30,
	(In thousands, except per share data)		2014		2013		2012
	Basic earnings per average common share:
	Net income applicable to common stock	$	105,940	$	80,253	$	139,818
	Average common shares outstanding—basic		51,759		51,697		51,522
	Basic earnings per average common share	$	2.05	$	1.55	$	2.71
	Diluted earnings per average common share:
	Net income applicable to common stock	$	105,940	$	80,253	$	139,818
	Average common shares outstanding—basic		51,759		51,697		51,522
	Stock-based compensation plans		11		111		67
	Total average common shares outstanding—diluted		51,770		51,808		51,589
	Diluted earnings per average common share	$	2.05	$	1.55	$	2.71

Income_Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2014
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	NOTE 9. INCOME TAXES
	WGL files consolidated, federal, combined unitary including California, District of Columbia, West Virginia and various other state income tax returns. We are no longer subject to income tax examinations by the Internal Revenue Service (IRS) for years before September 30, 2011. Substantially all state income tax years in major jurisdictions are closed for years before September 30, 2010.
	WGL and each of its subsidiaries also participate 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 of the parent, WGL, are allocated to the subsidiaries that have taxable income. In fiscal year 2014, Washington Gas shared $2.9 million of tax benefits from the tax sharing agreement that was reflected as a tax decrease on Washington Gas' statements of income. During fiscal years 2013 and 2012, Washington Gas realized $1.3 million and $0.3 million of tax savings as a result of this tax sharing agreement. The effect of this allocation of benefits to Washington Gas has no effect on our consolidated financial statements. State income tax returns are filed on a separate company basis in most states where we have operations and/or a requirement to file. Beginning with the fiscal year ended September 30, 2012, we filed a combined unitary return for California, District of Columbia and West Virginia due to recent law changes.
	Washington Gas provides certain healthcare benefits for active and retired employees (the Plan). Washington Gas is self-insured for the majority of healthcare costs. Because the Plan provides prescription drug benefits equal to or greater than Medicare Part D (Med D) coverage, Washington Gas qualified for a non-taxable subsidy from the federal government, which has had the effect of lowering other post retirement employee benefit expense (OPEB) and Washington Gas' effective tax rate.
	Since the year ended September 30, 2004, Washington Gas reflected the favorable tax benefit (“the Med D tax benefit”) of the non-taxable subsidy in its effective tax rate. The Patient Protection and Affordable Care Act and the Health Care and Education Reconciliation Act (collectively the “PPACA”) became law which eliminated future Med D tax benefits for Washington Gas' tax years beginning after September 30, 2013. During the fiscal year ended September 30, 2010, regulatory assets were increased by $42.2 million to reflect the probable recovery of the higher future tax expense from utility customers and an immaterial amount of tax expense was recorded related to the effect of the PPACA on our non-utility business. Based on positions taken by the SCC of VA in Washington Gas' rate case during the fiscal year ended September 30, 2011, we determined that it was not probable that the SCC of VA would permit recovery of this asset. Therefore, the Virginia portion of the regulatory asset related to the Med D benefit was charged to tax expense which resulted in an increase in the effective tax rate for the fiscal year ended September 30, 2011. Washington Gas charged the Maryland portion of the Med D regulatory asset to tax expense during the fiscal year ended September 30, 2012, based on positions taken by the PSC of MD in Washington Gas' rate case during the fiscal year that didn't permit recovery. Washington Gas received an order in the first quarter of the current fiscal year end September 30, 2014 in its recent rate case from the PSC of MD that will allow recovery of the Med D regulatory asset over a 5-year amortization period. Therefore the tax benefit has been recognized to reinstate the regulatory asset which results in a decrease in the effective rate for the fiscal year ended September 30, 2014. The Med D adjustments results in an effective tax rate at September 30, 2014 of 34.8%. The Med D adjustment results in an effective rate for Washington Gas at September 30, 2014 of 32.6%. In June 2013, the District of Columbia approved a 5-year amortization of the regulatory asset relating to Med D, which should have a minimal impact to the effective tax rate over the period allowed.
	On September 13, 2013, the U.S. Treasury Department issued final income tax regulations to address the costs incurred in acquiring, producing, or improving tangible property. The regulations are effective for WGL and Washington Gas for the tax year beginning October 1, 2014. WGL and Washington Gas have assessed the financial impact of these regulations, and we do not expect the guidance to have a material impact on the financial statements. Any changes in method of accounting for income tax purposes required to conform to the final regulations will be made for the taxable year ending September 30, 2015.
	The tables below provide the following for WGL and Washington Gas: (i) the components of income tax expense; (ii) a reconciliation between the statutory federal income tax rate and the effective income tax rate and (iii) the components of accumulated deferred income tax assets and liabilities at September 30, 2014 and 2013.
	WGL Holdings, Inc.
	Components of Income Tax Expense
		Years Ended September 30,
	(In thousands)		2014		2013		2012
	INCOME TAX EXPENSE
	Current:
	Federal	$	29,976	$	41,425	$	-13,188
	State		5,149		11,258		-30
	Total current		35,125		52,683		-13,218
	Deferred:
	Federal
	Accelerated depreciation		35,747		33,394		45,506
	Other		-18,014		-31,173		44,727
	State
	Accelerated depreciation		9,822		6,795		9,412
	Other		-1,760		-7,585		8,054
	Total deferred		25,795		1,431		107,699
	Amortization of investment tax credits		-3,666		-1,822		-1,132
	Total income tax expense	$	57,254	$	52,292	$	93,349
	WGL Holdings, Inc.
	Reconciliation Between the Statutory Federal Income Tax Rate and Effective Tax Rate
			Years Ended September 30,
	($ In thousands)		2014				2013				2012
	Income taxes at statutory federal income tax rate	$	57,580	35	%	$	46,853	35	%	$	82,070	35	%
	Increase (decrease) in income taxes resulting from:
	Accelerated depreciation less amount deferred		1,875	1.14			2,106	1.57			1,178	0.5
	Amortization of investment tax credits		-3,666	-2.23			-1,822	-1.36			-1,132	-0.48
	Cost of removal		-4,902	-2.98			-2,356	-1.76			-2,291	-0.98
	State income taxes-net of federal benefit		8,734	5.31			7,448	5.56			12,068	5.15
	Medicare Part D adjustment		-3,621	-2.2			-	-			2,827	1.21
	Other items-net		1,254	0.76			63	0.05			-1,371	-0.59
	Total income tax expense and effective tax rate	$	57,254	34.8	%	$	52,292	39.06	%	$	93,349	39.81	%
	WGL Holdings, Inc.
	Components of Deferred Income Tax Assets (Liabilities)
			September 30,
	(In thousands)		2014				2013
	ACCUMULATED DEFERRED INCOME TAXES	Current		Non-current		Current		Non-current
	Deferred income tax assets:
	Pensions	$	-	$	24,349	$	-	$	17,362
	Other post-retirement benefits		-		-		-		18,510
	Uncollectible accounts		9,268		-		8,127		-
	Inventory overheads		6,591		-		6,431		-
	Capital gains/losses-net		-		-		2		-
	Valuation allowance		-		-		-2		-
	Employee compensation and benefits		6,306		37,873		5,876		37,301
	Customer advances		-		197		-		197
	Derivatives		6,503		31,555		-		7,872
	Deferred gas costs		-		4,218		4,911		-
	Solar grant/investment tax credit		-		39,184		-		17,415
	Other		814		1,225		816		2,530
	Total assets		29,482		138,601		26,161		101,187
	Deferred income tax liabilities:
	Other post-retirement benefits		-		38,299		-		-
	Accelerated depreciation and other plant related items		-		669,040		-		596,754
	Losses/gains on reacquired debt		-		1,426		-		1,567
	Income taxes recoverable through future rates		-		65,374		-		112,222
Deferred gas costs		2,818		-		-		4,667
Derivatives		-		-		1,639		-
Partnership basis differences		-		25,370		-		15,784
Total liabilities		2,818		799,509		1,639		730,994
Net accumulated deferred income tax assets (liabilities)	$	26,664	$	-660,908	$	24,522	$	-629,807
Washington Gas Light Company
Components of Income Tax Expense
			Years Ended September 30,
(In thousands)			2014		2013		2012
INCOME TAX EXPENSE
Current:
Federal		$	37,098	$	40,492	$	-13,155
State			4,262		7,515		-3,332
Total current			41,360		48,007		-16,487
Deferred:
Federal
Accelerated depreciation			34,833		34,518		45,661
Other			-30,523		-35,982		27,851
State
Accelerated depreciation			9,540		6,770		9,423
Other			-6,800		-8,221		6,197
Total deferred			7,050		-2,915		89,132
Amortization of investment tax credits			-876		-895		-898
Total income tax expense		$	47,534	$	44,197	$	71,747
Washington Gas Light Company
Reconciliation Between the Statutory Federal Income Tax Rate and Effective Tax Rate
		Years Ended September 30,
($ In thousands)		2014				2013				2012
Income taxes at statutory federal income tax rate	$	51,050	35	%	$	40,782	35	%	$	63,628	35	%
Increase (decrease) in income taxes resulting from:
Accelerated depreciation less amount deferred		1,875	1.29			2,106	1.81			1,178	0.65
Amortization of investment tax credits		-876	-0.6			-895	-0.77			-898	-0.49
Cost of removal		-4,902	-3.36			-2,356	-2.02			-2,291	-1.26
State income taxes-net of federal benefit		6,711	4.6			5,487	4.71			8,916	4.9
Consolidated tax sharing allocation		-2,862	-1.96			-1,290	-1.11			-309	-0.17
Medicare Part D adjustment		-3,621	-2.48			-	-			2,827	1.56
Other items-net		159	0.09			363	0.31			-1,304	-0.72
Total income tax expense and effective tax rate	$	47,534	32.58	%	$	44,197	37.93	%	$	71,747	39.47	%
Washington Gas Light Company
Components of Deferred Income Tax Assets (Liabilities)
		Years Ended September 30,
(In thousands)		2014				2013
ACCUMULATED DEFERRED INCOME TAXES	Current		Non-current		Current		Non-current
Deferred income tax assets:
Pensions	$	-	$	23,738	$	-	$	16,768
Other post-retirement benefits		-		-		-		18,474
Uncollectible accounts		7,618		-		6,948		-
Inventory overheads		6,591		-		6,431		-
Employee compensation and benefits		5,902		27,961		5,756		27,125
Customer advances		-		197		-		197
Derivatives		4,809		31,555		2,138		7,872
Deferred gas costs		-		4,218		4,911		-
Investment tax credit		-		312		-		312
Other		814		-		816		1,727
Total assets		25,734		87,981		27,000		72,475
Deferred income tax liabilities:
Other post-retirement benefits		-		38,065		-		-
Accelerated depreciation and other plant related items		-		602,376		-		565,996
Losses/gains on reacquired debt		-		1,426		-		1,567
Income taxes recoverable through future rates		-		65,128		-		111,698
Deferred gas costs		2,818		-		-		4,667
Other		-		932		-		-
Total liabilities		2,818		707,927		-		683,928
Net accumulated deferred income tax assets (liabilities)	$	22,916	$	-619,946	$	27,000	$	-611,453
In June 2014, we filed our tax return for the year ended September 30, 2013.
The following table summarizes the change in unrecognized tax benefits during fiscal year 2014, 2013, 2012 and our total unrecognized tax benefits at September 30, under the provisions of ASC Topic 740, Income Taxes:
Unrecognized Tax Benefits
(In thousands)		2014		2013		2012
Total unrecognized tax benefits, October 1,	$	25,051	$	22,082	$	20,699
Increases in tax positions relating to current year		10,512		5,251		3,396
Decreases in tax positions relating to prior year		-2,950		-2,282		-2,013
Total unrecognized tax benefits, September 30,	$	32,613	$	25,051	$	22,082
During the year, the unrecognized tax benefits for WGL and Washington Gas increased by approximately $7.6 million relating to uncertain tax positions, primarily due to the change in tax accounting for repairs. 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 WGL's and Washington Gas' uncertain tax positions will increase or decrease in the next 12 months. The IRS completed its audit of the tax years related to the change in accounting method for repairs without proposing any changes, however, they could re-examine this issue in the future.
WGL and Washington Gas recognize 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 fiscal year ended September 30, 2014, we reversed minimal interest and during the fiscal year ended September 30, 2013 we accrued minimal interest expenses on uncertain tax positions. During the fiscal year ended September 30, 2012, we reversed $1.6 million for interest on uncertain tax positions.

Pension_and_Other_PostRetireme

Pension and Other Post-Retirement Benefit Plans	12 Months Ended
	Sep. 30, 2014
Pension and Other Post-Retirement Benefit Plans [Abstract]	'
Pension and Other Post-Retirement Benefit Plans	'
	NOTE 10. 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. The non-contributory defined benefit pension plan is closed to all employees hired on or after January 1, 2010. Washington Gas accounts for the qualified pension plan and other post-retirement benefit plans under the provisions of ASC 715, Compensation-Retirement Benefits.
	Most executive officers of Washington Gas also participate in a non-funded defined benefit supplemental executive retirement plan (DB SERP), a non-qualified pension plan. A rabbi trust has been established for the potential future funding of the DB SERP liability. The DB SERP was closed to new entrants beginning January 1, 2010 and instead, executive officers are eligible to participate in a new non-funded 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.
	WGL subsidiaries offer 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 by employees in accordance with the specific plan provisions. The Washington Gas plan was amended during 2013 to implement the merger of the WGEServices plan. The WGEServices plan was merged into the Washington Gas plan effective January 1, 2014. Beginning January 1, 2014, matching and supplemental contributions to the Washington Gas plan included matching and supplemental contributions from the former WGEServices plan. Total matching contributions to the Washington Gas plan were $4.2 million, $3.5 million and $3.4 million during fiscal years 2014, 2013 and 2012, respectively. All employees not participating 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 $1.6 million, $0.8 million and $0.6 million during fiscal years ended September 30, 2014, 2013 and 2012, respectively.
	Total matching contributions to the former WGEServices plan were $0.8 million and $0.4 million during fiscal years 2013 and 2012, respectively.
	Washington Gas provides certain healthcare and life insurance benefits for retired employees. Substantially all employees of Washington Gas may become eligible for such benefits if they attain retirement status while working for Washington Gas. Washington Gas accounts for these benefits under the provisions of ASC 715, Compensation-Retirement Benefits. Washington Gas elected to amortize the accumulated post-retirement benefit obligation of $190.6 million existing at the October 1, 1993 adoption date of this standard, known as the transition obligation, over a twenty-year period ended in 2013.
	On April 24, 2014, Washington Gas replaced the existing retiree medical benefit plan and dental plan options for Medicare-eligible retirees age 65 and older with a special tax-free Health Reimbursement Account (HRA) plan effective January 1, 2015. With the introduction of the new plan, effective January 1, 2015, participating retirees and dependents will receive a subsidy each year through the HRA account to help purchase supplemental medical 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. Retirees and dependents under age 65 will still be covered under the existing Washington Gas Retiree Medical Plan until they become eligible for Medicare at age 65 and can obtain coverage through the new HRA plan. Due to the impact of the amendment, we remeasured the funded status of the plan in April 2014. The funded status of the plan changed by approximately $127.5 million from an underfunded liability to an overfunded asset as a result of the plan amendment. The offsetting amount for this remeasurement was substantially recorded as a decrease to regulatory assets. The overfunded asset for this plan at September 30, 2014 was $96.4 million.
	Almost all costs associated with Washington Gas' defined benefit post-retirement plans have historically been, and will continue 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 September 30 for its pension, and retiree healthcare and life insurance benefit plans. The following table provides certain information about Washington Gas' post-retirement benefits:
	Post-Retirement Benefits
								Health and Life
	(In millions)			Pension Benefits(a)				Benefits
	Year Ended September 30,			2014		2013		2014		2013
	Change in projected benefit obligation(b)
	Benefit obligation at beginning of year		$	837.4	$	937.2	$	429.8	$	480.1
	Service cost			14		17		7.6		9.6
	Interest cost			40.4		36.6		18.7		18.8
	Change in plan benefits			-		-		-136.5		-
	Actuarial loss (gain)			68.6		-110		38.2		-62.3
	Retiree contributions			-		-		4.4		3.9
	Medicare Part D reimbursements			-		-		0.5		0.7
	Benefits paid			-43.3		-43.4		-19.5		-21
	Projected benefit obligation at end of year(b)		$	917.1	$	837.4	$	343.2	$	429.8
	Change in plan assets
	Fair value of plan assets at beginning of year		$	745.2	$	750.6	$	380.9	$	358.3
	Actual return on plan assets			103.3		38.6		57.8		19.9
	Company contributions			1.7		1.8		16		18
	Retiree contributions and Medicare Part D reimbursements			-		-		4.4		5.7
	Expenses			-2.2		-2.4		-		-
	Benefits paid			-43.3		-43.4		-19.5		-21
	Fair value of plan assets at end of year		$	804.7	$	745.2	$	439.6	$	380.9
	Funded status at end of year		$	-112.4	$	-92.2	$	96.4	$	-48.9
	Total amounts recognized on balance sheet
	Non-current asset		$	-	$	-	$	96.4	$	-
	Current liability			-4.2		-3.5		-		-
	Non-current liability			-108.2		-88.7		-		-48.9
	Total recognized		$	-112.4	$	-92.2	$	96.4	$	-48.9
	(a)The DB SERP and DB Restoration, included in pension benefits in the table above, have no assets.
	(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 (ABO) for the qualified pension plan, DB SERP and DB Restoration at September 30, 2014 and 2013.
	Projected and accumulated benefit obligation
	(In millions)		Qualified Pension Plan				DB SERP				DB Restoration
	September 30,	2014		2013		2014		2013		2014		2013
	Projected benefit obligation	$	865.2	$	788.8	$	50.7	$	47.8	$	1.2	$	0.8
	Accumulated benefit obligation	$	801.9	$	737.2	$	46.2	$	43.9	$	0.7	$	0.5
	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 at September 30, 2014 and 2013:
	Unrecognized Costs/Income Recorded on the Balance Sheet
	(In millions)				Pension Benefits				Health and Life Benefits
	September 30,			2014		2013		2014		2013
	Actuarial net loss			$	162.6	$	171.1	$	50.1	$	55.3
	Prior service cost (credit)				1.2		1.3		-149.3		-22.4
	Total			$	163.8	$	172.4	$	-99.2	$	32.9
	Regulatory asset (liability)			$	147.9	$	155.1	$	-94.6	$	31.3
	Pre-tax accumulated other comprehensive loss (gain)(a)				15.9		17.3		-4.6		1.6
	Total			$	163.8	$	172.4	$	-99.2	$	32.9
	(a)The total amount of accumulated other comprehensive loss recorded on our balance sheets at September 30, 2014 and 2013 is net of an income tax benefit of $4.9 million and $7.9 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 during fiscal year 2014.
	Amounts Recognized During Fiscal Year 2014
		Regulatory assets/liabilities					Accumulated other comprehensive loss
	(In millions)	Pension Benefits		Health and Life Benefits			Pension Benefits		Health and Life Benefits
	Actuarial net loss	$	15.5	$	4.8		$	1.3	$	0.3
Prior service cost (credit)		0.2		-9.1			0.1		-0.5
Total	$	15.7	$	-4.3		$	1.4	$	-0.2
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 during fiscal year 2015.
Amounts to be Recognized During Fiscal Year 2015
	Regulatory assets/liabilities					Accumulated other comprehensive loss
(In millions)	Pension Benefits		Health and Life Benefits			Pension Benefits		Health and Life Benefits
Actuarial net loss	$	17.1	$	4.2		$	1.7	$	0.2
Prior service cost (credit)		0.2		-14.5			0.1		-0.7
Total	$	17.3	$	-10.3		$	1.8	$	-0.5
The increase in the actuarial net loss for pension benefits to be recognized in fiscal year 2015 when compared to fiscal year 2014 is primarily due to a decrease in the discount rate for our qualified pension plan. The decrease in the actuarial net loss for health and life benefits to be recognized in fiscal year 2015 when compared to fiscal year 2014 is primarily due to updated census data, offset by a decrease in the discount rate for our health and life plan.
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 fiscal years ended September 30, 2014, 2013 and 2012 related to pension and other postretirement benefits were as follows:
Components of Net Periodic Benefit Costs (Income)
(In millions)			Pension Benefits						Health and Life Benefits
Year Ended September 30,			2014		2013		2012		2014		2013		2012
Service cost		$	14	$	17	$	12.9	$	7.6	$	9.6	$	8
Interest cost			40.4		36.6		40.5		18.7		18.8		25.1
Expected return on plan assets			-41		-41.9		-43.5		-19.3		-18.3		-18.8
Recognized prior service cost			0.3		1		1		-9.6		-3.9		-3.9
Recognized actuarial loss			16.8		28.7		16.1		5		9.2		13.3
Amortization of transition obligation			-		-		-		-		1.1		1.1
Net periodic benefit cost			30.5		41.4		27		2.4		16.5		24.8
Amount allocated to construction projects			-4.3		-5.7		-3.4		-0.4		-2.8		-3.7
Amount deferred as regulatory asset (liability)-net			7		-3.7		-7.5		-2.3		2.4		1.5
Amount charged (credited) to expense		$	33.2	$	32	$	16.1	$	-0.3	$	16.1	$	22.6
Amounts included in the line item “Amount deferred as regulatory asset/liability-net,” represent the difference between the cost of the applicable pension benefits and the health and life benefits and the amount that Washington Gas is permitted to recover in rates that it charges to customers in the District of Columbia. In June 2013, this mechanism was discontinued, however, any balances remaining will be amortized over five years.
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
September 30,			2014	2013		2014	2013
Discount rate(a)			4.00%-4.40%	4.50%-5.00%		4.40%	5.10%
Rate of compensation increase			3.50%-4.10%	3.85%-5.15%		4.10%	3.85%
(a)The decrease in the discount rate in fiscal year 2014 compared to prior years primarily reflects the decrease in long-term interest rates.
Net Periodic Benefit Cost Assumptions
	Pension Benefits				Health and Life Benefits
Years Ended September 30,	2014	2013	2012		2014	2013	2012
Discount rate(a)	4.50%-5.00%	4.00%	5.30%		4.60%-5.10%	4.00%	5.10%
Expected long-term return on plan assets(b)	6.50%	6.75%	7.50%		6.25%	6.75%	7.40%
Rate of compensation increase(c)	3.85%-5.15%	3.85%-5.15%	3.85%-5.15%		3.85%	3.85%	3.85%-5.15%
(a) The changes in the discount rates over the last two fiscal years primarily reflects 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 41.5%.
(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.
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.
Washington Gas assumed the healthcare cost trend rates related to the accumulated post-retirement benefit obligation for non-Medicare eligible retirees to be 7.0% and 7.5% for fiscal years 2014 and 2013, respectively. Washington Gas expects these rates to decrease gradually to 5.0% in 2021 and remain at those levels thereafter. For Medicare eligible retirees age 65 and older that will receive a subsidy each year through an HRA account, Washington Gas assumed a 3.0% increase 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.
Healthcare Trends
(In millions)	One Percentage-Point Increase				One Percentage-Point Decrease
Increase (decrease) total service and interest cost components	$	3.6			$	-2.7
Increase (decrease) post-retirement benefit obligation	$	10.5			$	-9.2
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.
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. 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 and to lengthen the duration of those fixed income assets. Both changes result in a better matching of each Plan's assets and liabilities, and help reduce volatility of each Plan's funded status. Implementation of these fixed income strategies occurred during fiscal year 2010 for the qualified pension plan and during fiscal year 2011 for the healthcare and life insurance benefit plans.
A pension plan ALM study that was completed during November 2011 resulted in a one-way dynamic asset allocation strategy that allows for the de-risking of the portfolio over time. Under this strategy, the target fixed income allocation percentage will increase by 5% for each 5% improvement in the plan's funded ratio, as measured by an investment consultant. This strategy resulted in portfolio de-risking during October 2012 including increased fixed income exposure and reduced U.S. large-cap equity exposure.
For the qualified pension plan, Washington Gas' funding policy is to contribute an amount sufficient to satisfy the minimum annual funding requirements under the Pension Protection Act. Any contributions above the minimum annual funding requirements would be limited to amounts that are deductible under appropriate tax law. For the healthcare and life insurance benefit plans, Washington Gas' funding policy is to contribute amounts that are collected from ratepayers.
Significant amounts of the various Plans' assets are managed by the same financial institution. In addition, the Plans have 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.
Target qualified pension plan trust asset allocations are 32.5% U.S. Large-Cap Equities, 4.5% U.S. Small/Mid-Cap Equities, 8% International Equities, 5% Real Estate, and 50% Fixed Income.
Washington Gas' portion of retired employee healthcare and life insurance benefits obligation is funded through two trusts: (i) the Washington Gas Light Company Postretirement Benefit Master Trust for Retired Previously Union-Eligible Employees ("union-eligible trust") and (ii) the Washington Gas Light Company Postretirement Benefit Master Trust for Retired Management Employees ("management trust"). Target asset allocations are 50% U.S. Large-Cap Equities and 50% Fixed Income for the union-eligible trust. Target allocations are 60% U.S. Large-Cap Equities and 40% Fixed Income for the management trust.
Actual asset balances are reviewed monthly, and are 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.
Investment vehicles used to manage qualified pension plan trust and management trust assets include commingled funds and separately managed portfolios. A private placement mutual fund is also employed to manage a portion of qualified pension plan trust assts. Commingled funds are used in the management of union-eligible trust assets.
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 by asset category as of September 30, 2014 and 2013:
	Pension Plan Assets
											% of
	($ In millions)		Level 1		Level 2		Level 3		Total		Total
	At September 30, 2014
	Cash and cash equivalents		$	0.6	$	-	$	-	$	0.6	0.1	%
	Equity securities
		U.S. Small Cap		32.3		-		-		32.3	4
		Preferred Securities		-		0.1		-		0.1	0
	Fixed income securities
		U.S. Treasuries		-		110.6		-		110.6	13.8
		U.S. Corporate Debt		-		108.4		-		108.4	13.5
		U.S. Agency Obligations and Government Sponsored Entities		-		24.6		-		24.6	3
		Asset-Backed Securities and Collateralized Mortgage Obligations		-		1.8		-		1.8	0.2
		Municipalities		-		9.2		-		9.2	1.1
		Non-U.S. Corporate Debt		-		23.8		-		23.8	3
		Repurchase Agreements(a)		-		2.5		-		2.5	0.3
		Other(b)		-		7		-		7	0.8
	Mutual Funds(c)			-		112.4		-		112.4	14
	Commingled Funds and Pooled Separate Accounts(d)			-		316.2		23.8		340	42.3
	Private Equity/Limited Partnerships(e)			-		30.5		-		30.5	3.8
	Derivatives(f)			-		-0.1		-		-0.1	0
	Total fair value of plan investments		$	32.9	$	747	$	23.8	$	803.7	99.9	%
	Receivable (payable)(g)									1	0.1
	Total plan assets at fair value								$	804.7	100	%
Pension Plan Assets
										% of
($ In millions)		Level 1		Level 2		Level 3		Total		Total
At September 30, 2013
Cash and cash equivalents		$	0.9	$	-	$	-	$	0.9	0.1	%
Equity securities
	U.S. Small Cap		31.5		-		-		31.5	4.2
	Preferred Securities		-		0.1		-		0.1	-
Fixed income securities
	U.S. Treasuries		-		124.5		-		124.5	16.7
	U.S. Corporate Debt		-		93.6		-		93.6	12.6
	U.S. Agency Obligations and Government Sponsored Entities		-		19		-		19	2.5
	Asset-Backed Securities and Collateralized Mortgage Obligations		-		1.9		-		1.9	0.2
	Municipalities		-		9		-		9	1.2
	Non-U.S. Corporate Debt		-		18.4		-		18.4	2.5
	Repurchase Agreements(a)		-		1		-		1	0.1
	Other(b)		-		5.7		-		5.7	0.8
Mutual Funds(c)			-		93.2		-		93.2	12.5
Commingled Funds and Pooled Separate Accounts(d)			-		295.5		21.1		316.6	42.5
Private Equity/Limited Partnerships(e)			-		33.3		-		33.3	4.5
Derivatives(f)			-		-0.3		-		-0.3	-
Total fair value of plan investments		$	32.4	$	694.9	$	21.1	$	748.4	100.4	%
Receivable (payable)(g)									-3.2	-0.4
Total plan assets at fair value								$	745.2	100	%
(a)	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.
(b)	This category primarily includes Yankee bonds and non-U.S. government bonds.
(c)	At September 30, 2014 and September 30, 2013, investments in mutual funds consisted primarily of corporate fixed income instruments.
(d)	At September 30, 2014, investments in commingled funds and pooled separate accounts consisted primarily of 75% common stock of large-cap U.S. companies; 14% income producing properties located in the United States; 9% equity securities of non-U.S. companies; and 2% short-term money market investments. At September 30, 2013, investments in commingled funds and pooled separate accounts consisted primarily of 67% common stock of large-cap U.S. companies; 12% income producing properties located in the United States; 20% equity securities of non-U.S. companies; and 1% short-term money market investments.
(e)	At September 30, 2014, investments in private equity/limited partnership consisted of common stock of international companies.
(f)	At September 30, 2014, this category includes long-term U.S. Treasury interest rate futures contracts and interest rate put options.
(g)	At September 30, 2014, this receivable represents a pending trade for investment sales. At September 30, 2013, this payable represents a pending trade for investment purchases.
Healthcare and Life Insurance Plan Assets
										% of
($ In millions)			Level 1		Level 2		Level 3		Total	Total
At September 30, 2014
Cash and Cash Equivalents		$	0.8	$	-	$	-	$	0.8	0.2	%
Mutual Funds(a)			-		1.9		-		1.9	0.4
Fixed Income Securities
	U.S Agency Obligations		-		2		-		2	0.5
	U.S. Treasuries		-		25.6		-		25.6	5.8
	U.S. Corporate Debt		-		34		-		34	7.7
	Municipalities		-		4.8		-		4.8	1.1
	Non-U.S. Corporate Debt		-		5.7		-		5.7	1.3
	Others(b)		-		5.3		-		5.3	1.2
Commingled Funds(c)			-		359.7		-		359.7	81.8
Total fair value of plan investments		$	0.8	$	439	$	-	$	439.8	100	%
Receivable (payable)									-0.2	-
Total plan assets at fair value								$	439.6	100	%
At September 30, 2013
Cash and Cash Equivalents		$	0.6	$	-	$	-	$	0.6	0.2	%
Fixed Income Securities
	U.S Agency Obligations		-		1.7		-		1.7	0.4
	U.S. Treasuries		-		23.6		-		23.6	6.2
	U.S. Corporate Debt		-		28.7		-		28.7	7.5
	Municipalities		-		4.1		-		4.1	1.1
	Non-U.S. Corporate Debt		-		4.6		-		4.6	1.2
	Others(b)		-		5.3		-		5.3	1.4
Commingled Funds(c)			-		311.2		-		311.2	81.7
Total fair value of plan investments		$	0.6	$	379.2	$	-	$	379.8	99.7	%
Receivable (payable)									1.1	0.3
Total plan assets at fair value								$	380.9	100	%
(a)	At September 30, 2014, investments in mutual funds consisted primarily of 63% short-term obligations consisting of certificates of deposit and time deposits, 23% high-quality commercial paper, 6% repurchase agreements, 4% corporate notes of U.S. and foreign corporations and 4% U.S. governmental and U.S. agency securities.
(b)	At September 30, 2014 and 2013, this category consisted primarily of 82% non-U.S. government bonds and 18% Yankee bonds.
(c)	At September 30, 2014 and 2013, investments in commingled funds consisted primarily of 66% common stock of large-cap U.S. companies, 17% U.S. agency obligations and government sponsored entities and 17% corporate bonds.
Valuation Methods
Equity securities are traded on a securities exchange and are valued at the closing quoted market price as of the balance sheet date.
Mutual funds are valued at the quoted net asset value (NAV) per share, which is computed as of the close of business on the balance sheet date. Mutual funds with a publicly quoted NAV per share are classified as Level 1; mutual funds with a NAV per share that is not made publicly available are classified as Level 2. Real Estate Investment Funds which have redemption restrictions are classified as Level 3.
Commingled funds and pooled separate accounts are valued at the quoted NAV per unit, computed as of the close of business on the balance sheet date.
Private Equity/Limited Partnership funds are valued at the quoted NAV, which is computed monthly and allocated based on ownership interest in partners' capital.
Fixed income securities are valued using pricing models that consider various observable inputs such as benchmark yields, reported trades, broker quotes and issuer spreads to determine fair value.
The Plans may engage in repurchase transactions. Generally, in accordance with the terms of a repurchase agreement, the Plans take possession of Treasury Bills in exchange for cash and the counterparty is obligated to repurchase, and the Plan to resell, the same securities at an agreed-upon price and time. The repurchase agreements have a one-day maturity and a fair value equal to the Plan's cash outlay at the time the agreement is executed.
The following table summarizes the changes in the fair value of the Level 3 assets for the fiscal years ended 2014 and 2013:
	(In millions)
	Years Ended September 30,			2014			2013
	Balance, beginning of year			$	21.1		$	18.7
	Actual return on plan assets:
		Assets still held at year end			2.7			2.4
	Balance, end of year			$	23.8		$	21.1
Benefit Contribution
During fiscal year 2014, Washington Gas did not contribute to its qualified pension but did contribute $1.8 million to its non-funded DB SERP plan. During fiscal year 2015, Washington Gas does not expect to make a contribution to its qualified pension plan and expects to make a payment of $4.1 million to its non-funded DB SERP. During fiscal year 2014, Washington Gas contributed $16.0 million to its health and life insurance benefit plans. Washington Gas expects to make a contribution of $16.6 million to its health and life insurance benefit plans during fiscal year 2015.
Expected Benefit Payments
Expected benefit payments, including benefits attributable to estimated future employee service, which are expected to be paid over the next ten years are as follows:
	Expected Benefit Payments
	(In millions)	Pension Benefits			Health and Life Benefits
	2015	$	48.9		$	17.9
	2016		50.3			18.8
	2017		51.9			19.4
	2018		53			20.1
	2019		54.7			20.6
	2020—2024		286.5			105.3
MEDICARE SUBSIDY RECEIPTS / EMPLOYER GROUP WAIVER PLAN
Prior to 2013 Washington Gas sponsored a post-65 retiree prescription drug plan that was at least actuarially equivalent to Medicare (Medicare Part D), and as a result was eligible to receive a federal subsidy under the Medicare Prescription Drug, Improvement and Modernization Act of 2003. Effective January 1, 2013 Washington Gas implemented an Employer Group Waiver Plan with a wraparound supplemental plan ("EGWP/wrap"). Accordingly, the Washington Gas retiree medical plan began receiving direct reimbursements and discounts from Medicare and the large pharmaceutical companies. During the year ended September 30, 2014, Washington Gas received $0.5 million in reimbursements related to the EGWP/wrap. Effective January 1, 2015, Washington Gas will cease to participate in the EGWP/wrap because participants age 65 and older will be transitioning into the new WGL Retiree HRA Plan, where such participants will receive an annual stipend that could be used to purchase health and prescription drug insurance.
REGULATORY MATTERS
A significant portion of the estimated pension and post-retirement medical and life insurance benefits apply to our regulated activities. Each regulatory commission having jurisdiction over Washington Gas requires it to fund amounts reflected in rates for post-retirement medical and life insurance benefits into irrevocable trusts.
District of Columbia Jurisdiction
Washington Gas recovers all costs allocable to the District of Columbia associated with its qualified pension plan and other post-retirement medical and life insurance benefits. Expenses of the SERP allocable to the District of Columbia are not recovered through rates. The PSC of DC granted the recovery of post-retirement medical and life insurance benefit costs determined in accordance with GAAP through a five-year phase-in plan that ended September 30, 1998. Washington Gas deferred the difference generated during the phase-in period as a regulatory asset. Effective October 1, 1998, the PSC of DC granted Washington Gas full recovery of costs determined under GAAP, plus a fifteen-year amortization of the regulatory asset established during the phase-in period that ended in fiscal year 2014.
Virginia Jurisdiction
On September 28, 1995, the SCC of VA issued a generic order that allowed Washington Gas to recover most costs determined under GAAP for post-retirement medical and life insurance benefits in rates over twenty years. The SCC of VA, however, set a forty-year recovery period of the transition obligation. As prescribed by GAAP, Washington Gas amortizes these costs over a twenty-year period. With the exception of the transition obligation, the SCC of VA has approved a level of rates sufficient to recover annual costs for all pension and other post-retirement medical and life insurance benefit costs determined under GAAP.
Maryland Jurisdiction
In Washington Gas' most recent rate case, the PSC of MD approved 50% of the expenses of the SERP for recovery through rates. The PSC of MD has approved a level of rates sufficient to recover pension and other post-retirement benefit costs as determined under GAAP.

Stock_Based_Compensation

Stock Based Compensation	12 Months Ended
	Sep. 30, 2014
Share-based Compensation [Abstract]	'
Disclosure of Compensation Related Costs, Share-based Payments [Text Block]	'
	NOTE 11. STOCK-BASED COMPENSATION
	STOCK-BASED COMPENSATION FOR KEY EMPLOYEES
	We have stock-based awards outstanding in the form of stock options, performance shares and performance units. We have stock options outstanding under our shareholder-approved 1999 Incentive Compensation Plan, as amended and restated (1999 Plan). In March 2007, WGL adopted a shareholder-approved Omnibus Incentive Compensation Plan (Omnibus Plan) to replace, on a prospective basis, the 1999 Plan. Stock options, stock appreciation rights, restricted stock, deferred stock and stock as a bonus in lieu of other awards, dividend equivalents, other stock-based awards and cash awards may be granted under the Omnibus Plan. The Omnibus Plan allows WGL to issue up to 1,700,000 shares of common stock, subject to adjustment as provided by the plan, to persons including officers and key employees, designated by the Human Resources Committee of the Board of Directors. Refer to Note 6—Common Stock—WGL for amounts remaining to be issued under these plans.
	During the fiscal year ended September 30, 2014, we granted performance shares and performance units under the Omnibus Plan. We have not issued stock options under either plan since October 2006. As of September 30, 2014, there are prior years' stock option grants outstanding for which the exercise price is equal to the market value of our common stock on the date of the grant.
	For both performance shares and performance units, the actual award that may be earned varies based on the total shareholder return of WGL relative to a selected peer group of companies. These performance awards generally vest over three years from the date of grant. Performance shares earned are paid in shares of common stock of WGL. Performance units are earned pursuant to terms of the grant, are paid in cash and are valued at $1.00 per performance unit. Outstanding stock options vest over three years from the date of the grant and expire ten years thereafter. Performance units, performance shares and stock option awards provide for accelerated vesting upon a change in control of WGL. Additionally, outstanding stock options provide for accelerated vesting upon retirement, death or disability of the recipient. We generally issue new shares of common stock to provide for redemption of performance shares and stock options; however, we may, from time to time, repurchase shares of our common stock on the open market in order to meet these requirements. Both performance shares and stock options are accounted for as equity awards, and performance units are accounted for as liability awards as they are settled in cash.
	For the years ended September 30, 2014, 2013 and 2012, we recognized stock-based compensation expense of $3.4 million, $6.5 million and $3.6 million, net of related income tax benefits of $1.3 million, $2.6 million and $1.4 million, respectively.
	As of September 30, 2014, total unrecognized compensation expense related to stock-based awards granted was $6.5 million. Performance shares and performance units comprised $4.0 million and $2.5 million of total unrecognized compensation expense, respectively. The total unrecognized compensation expense is expected to be recognized over a weighted average cost period of 1.7 years for performance shares and performance units.
	Performance Shares
	The following table summarizes information regarding performance share activity during the fiscal year ended September 30, 2014.
	Performance Share Activity
		Year Ended
		30-Sep-14
		Number of Shares(a)		Weighted Average Grant-Date Fair Value
	Non-vested and outstanding, beginning of year	295,973		$	39.88
	Granted	109,076			42.88
	Vested	-84,849			41.14
	Cancelled/forfeited	-18,822			40.47
	Non-vested and outstanding, end of year	301,378		$	40.57
	(a)The number of common shares issued related to performance shares may range from zero to 200 percent of the number of shares shown in the table above based on our achievement of performance goals for total shareholder return relative to a selected peer group of companies.
	The total fair value of the performance shares outstanding at September 30, 2014 for the shares expected to vest in the future was $11.6 million. The total intrinsic value of performance shares vested during the year ended September 30, 2014 was $2.2 million. No performance shares vested during the year ended September 30, 2013. The total intrinsic value of performance shares vested during the year ended September 30, 2012 was $3.3 million.
	We measure compensation expense related to performance shares based on the fair value of these awards at their date of grant. Compensation expense for performance shares is recognized for awards that ultimately vest and is not adjusted based on the actual achievement of performance goals. We estimated the fair value of performance shares on the date of grant using a Monte Carlo simulation model and the following assumptions:
	Fair Value Assumptions
	Years Ended September 30,	2014			2013			2012
	Expected stock-price volatility		19.1	%		19.4	%		27.8	%
	Dividend yield		3.93	%		3.98	%		3.97	%
	Weighted average grant-date fair value	$	42.88		$	39.73		$	38.99
	Expected stock-price volatility is based on the daily historical volatility of our common shares for the past three fiscal years. The dividend yield represents our annualized dividend yield on the closing market price of our common stock at the date of the grant.
	Performance Units
	Our performance units are liability awards as they 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. Consequently, fluctuations in earnings may result that do not occur under the accounting requirements for both our stock options and performance shares.
	The following table summarizes information regarding performance unit activity during the fiscal year ended September 30, 2014.
	Performance Unit Activity
		Year Ended
		30-Sep-14
		Number of Units
	Non-vested and outstanding, beginning of year	11,582,556
	Granted	4,658,648
	Vested	-3,205,636
	Cancelled/forfeited	-766,647
	Non-vested and outstanding, end of year	12,268,921
	The total fair value of performance units outstanding at September 30, 2014 for the units expected to vest in the future was $4.9 million. As of September 30, 2014, 2013 and 2012, we recorded a liability of $2.4 million, $4.9 million and $2.1 million, respectively, related to our performance units. This liability is recorded in “Deferred Credits—other”. During the fiscal year ended September 30, 2014, we paid $2.0 million in cash to settle performance unit awards. During fiscal year ended September 30, 2013, we did not make any cash payments to settle performance unit awards. During the fiscal year ended September 30, 2012, we paid $2.8 million in cash to settle performance unit awards.
	We estimated the fair value of performance units using a Monte Carlo simulation model. The following table provides the year-end assumptions used to value our performance units:
	Fair Value Assumptions
		30-Sep-14
		10/1/2013 Grant	10/1/2012 Grant
	Expected stock-price volatility	18.10%	19.50%
	Expected stock-price volatility is based on the daily historical volatility of our common shares for a period equal to the remaining term of the performance units.
	Stock Options
	The following table summarizes information regarding stock option activity during the fiscal year ended September 30, 2014.
	Stock Option Activity
		Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (In years)	Aggregate Intrinsic Value (In thousands)
	Outstanding at September 30, 2013	26,372			$	31.34	4.01	$	235
	Granted	-				-	-		-
	Exercised	-21,054				31.34	-		232
	Cancelled/forfeited	-				-	-		-
	Outstanding at September 30, 2014	5,318			$	31.34	2	$	57
	Exercisable at September 30, 2014	5,318			$	31.34	2	$	57
	We received $0.7 million from the exercise of stock options during the year ended September 30, 2014. There were no stock options exercised during the year ended September 30, 2013 and no related tax benefits realized. We received $0.8 million from the exercise of stock options during the year ended 2012. The related tax benefits realized for the fiscal years ended September 30, 2014 and 2012 were $0.1 million and $0.1 million, respectively.
	We measure compensation expense related to stock options based on the fair value of these awards at their date of grant. Compensation expense for stock options is recognized for awards that ultimately vest. We estimated the fair value of stock options on the date of the grant using the Black-Scholes option-pricing model.
	Expected stock-price volatility is based on the daily historical volatility of our common shares over a period that approximates the expected term of the stock options. The dividend yield represents our annualized dividend yield on the closing market price of our common stock at the date of grant. The risk-free interest rate is based on the zero-coupon U.S. Treasury bond, with a term equal to the expected term of the stock options. The expected option term is based on our historical experience with respect to stock option exercises and expectations about future exercises.
	STOCK GRANTS TO DIRECTORS
	Non-employee directors receive a portion of their annual retainer fee in the form of common stock through the Directors' Stock Compensation Plan. Up to 270,000 shares of common stock may be awarded under the plan. Shares granted to directors were approximately 17,000, 16,600 and 11,900 for the fiscal years ended September 30, 2014, 2013 and 2012, respectively. For those years, the weighted average fair value of the stock on the grant dates was $40.06, $40.46, and $44.30, respectively. Shares awarded to the participants; (i) vest immediately and cannot be forfeited; (ii) may be sold or transferred and (iii) have voting and dividend rights. For each of the years ended September 30, 2014 and 2013, WGL recognized stock-based compensation expense related to stock grants of $0.7 million, net of related income tax benefits of $0.3 million. For the year ended September 30, 2012, WGL recognized stock-based compensation expense related to stock grants of $0.5 million, net of related income tax benefits of $0.2 million.

Environmental_Matters

Environmental Matters	12 Months Ended
	Sep. 30, 2014
Environmental Matters [Abstract]	'
Environmental Loss Contingency Disclosure [Text Block]	'
	NOTE 12. 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. Based on the information available to us, we have concluded that none of the sites are likely to present an unacceptable risk to human health or the environment, and either the appropriate remediation is being undertaken, or Washington Gas believes no remediation is necessary.
	At both September 30, 2014 and 2013, Washington Gas recorded a liability of $8.5 million, on an undiscounted basis related to future environmental response costs, which included the estimated costs for four MGP sites. These estimates principally include the minimum liabilities associated with a range of environmental response costs expected to be incurred at the sites identified. At September 30, 2014 and 2013, Washington Gas estimated the maximum liability associated with all of its sites to be approximately $19.3 million and $20.5 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 at each site and the extent of remediation that may be required.
	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 both September 30, 2014 and 2013, Washington Gas reported a regulatory asset of $0.6 million, for the portion of environmental response costs that are expected to be recoverable in future rates.
	We do not expect that the ultimate impact of these matters will have a material effect on our financial position, cash flows, capital expenditures, earnings or competitive position.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	NOTE 13. COMMITMENTS AND CONTINGENCIES
	OPERATING LEASES
	Minimum future rental payments under operating leases over the next five years and thereafter are as follows:
	Minimum Payments Under Operating Leases
	(In millions)
	2015	$	7.8
	2016		6.3
	2017		4.9
	2018		4.3
	2019		1
	Thereafter		10.5
	Total	$	34.8
	Rent expense totaled $5.5 million, $5.6 million and $5.2 million in fiscal years ended September 30, 2014, 2013 and 2012, respectively.
	REGULATED UTILITY OPERATIONS
	Natural Gas Contracts—Minimum Commitments
	At September 30, 2014, 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 fiscal years 2015 to 2032, 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 2015 to 2032. 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 fiscal years and thereafter. The gas purchase contracts noted below represent commitments to purchase natural gas based on market conditions at the time the natural gas is purchased.
		Washington Gas Contract Minimums
		(In millions)		Pipeline Contracts(a)			Gas Purchase Commitments(b)
		2015		$	195.4		$	280
		2016			224.7			288.9
		2017			217.7			336.7
		2018			211.1			323.2
		2019			201.3			303.5
		Thereafter			1,205.30			2,990.20
		Total		$	2,255.50		$	4,522.50
		(a) Represents minimum payments for natural gas transportation, storage and peaking contracts that have expiration dates through fiscal year 2032.
		(b) The contracts referenced above are estimated based on market prices at September 30, 2014.
	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.
	Currently, Washington Gas recovers its cost of gas to serve its customers through the purchased gas cost recovery mechanisms included in its retail rate schedules in each of its jurisdictions. However, the timing and extent of Washington Gas' initiatives or regulatory requirements to separate the purchase and sale of natural gas from the delivery of gas could cause its gas supply commitments to exceed its continued sales obligations.
	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.
	Regulatory Contingencies
	Certain legal and administrative proceedings incidental to our business, including regulatory contingencies, involve WGL and/or its subsidiaries. In our opinion, we have recorded an adequate provision for probable losses or refunds to customers for regulatory contingencies related to these proceedings.
	NON-UTILITY OPERATIONS
	WGEServices enters into contracts to purchase natural gas and electricity designed to match the duration of its sales commitments, and to effectively lock in a margin on estimated sales over the terms of existing sales contracts. As listed below, natural gas purchase commitments are based on existing fixed-price purchase contracts using city gate equivalent deliveries, the majority of which are for fixed volumes. Also listed below are electricity purchase commitments that are based on existing fixed-price purchase commitments, all of which are for fixed volumes.
	WGL Midstream enters into contracts to acquire, invest in, manage and optimize natural gas storage and transportation assets. Gas purchase commitments increased during fiscal year 2014 due to purchase commitments related to investment pipeline infrastructure.
	The following table summarizes the minimum commitments and contractual obligations of WGEServices and WGL Midstream for the next five fiscal years and thereafter:
		Contract Minimums
		WGEServices						WGL Midstream
	(In millions)	Gas Purchase Commitments(a)		Pipeline Contracts(b)		Electric Purchase Commitments(c)		Gas Purchase Commitments(d)		Pipeline Contracts(e)			Total
	2015	$	167.5	$	2.4	$	359.4	$	29.2	$	15.3	$	573.8
	2016		49.2		0.6		171.7		24.4		19.4		265.3
	2017		13.8		0.6		65		80.2		17.7		177.3
	2018		0.6		0.6		3.6		906		26.5		937.3
	2019		-		0.6		-		933.4		24.6		958.6
	Thereafter		-		1.3		-		13,479.80		260.9		13,742.00
	Total	$	231.1	$	6.1	$	599.7	$	15,453.00	$	364.4	$	16,654.30
	(a)Represents fixed price commitments with city gate equivalent deliveries.
	(b)Represents minimum payments for natural gas transportation, storage and peaking contracts that have expiration dates through fiscal year 2025.
	(c)Represents electric purchase commitments that are based on existing fixed price and fixed volume contracts. Includes $15.3 million of commitments related to renewable energy credits.
	(d)Includes short-term commitments to purchase fixed volumes of natural gas, as well as long-term gas purchase commitments that contain fixed volume purchase requirements. Cost estimates are based on forward market prices for purchases under these purchase commitments.
	(e)Represents minimum payments for natural gas transportation, storage and peaking contracts that have expiration dates through fiscal year 2044.
	Construction Project Financing
	To fund certain of its construction projects, Washington Gas enters into financing arrangements with third party lenders. As part of these financing arrangements, Washington Gas' customers agree to make principal and interest payments over a period of time, typically beginning after the projects are completed. Washington Gas assigns these customer payment streams to the lender. As the lender funds the construction project, Washington Gas establishes a receivable representing its customers' obligations to remit principal and interest and a long-term payable to the lender. When these projects are formally “accepted” by the customer as completed, Washington Gas transfers the ownership of the receivable to the lender and removes both the receivable and the long-term financing from its financial statements. As of September 30, 2014 and 2013, work on these construction projects that was not completed or accepted by customers was valued at $8.3 million and $6.7 million, respectively, that are recorded on the balance sheet as a receivable in “Deferred Charges and Other Assets—Other” with the corresponding long-term obligation to the lender in “Long-term debt.” At any time before these contracts are accepted by the customer, should there be a contract default, such as, among other things, a delay in completing the project, the lender may call on Washington Gas to fund the unpaid principal in exchange for which Washington Gas would receive the right to the stream of payments from the customer. Construction projects are financed primarily for government agencies, which Washington Gas considers to have minimal credit risk. Based on this assessment and previous collection experience, Washington Gas did not record a corresponding reserve for bad debts related to these receivables at September 30, 2014 or September 30, 2013.
	Financial Guarantees
	WGL has guaranteed payments primarily for certain purchases of natural gas and electricity on behalf of WGEServices and for certain purchase commitments on behalf of WGL Midstream. At September 30, 2014, these guarantees totaled $227.3 million and $276.5 million for WGEServices and WGL Midstream, respectively. At September 30, 2014, the guarantees relating to WGESystems totaled $6.0 million. The amount of such guarantees is periodically adjusted to reflect changes in the level of financial exposure related to these purchase commitments. For all of our financial guarantees, WGL may cancel any or all future obligations upon written notice to the counterparty, but WGL would continue to be responsible for the obligations created under the guarantees prior to the effective date of the cancellation. WGL also has guaranteed payments for certain of our other external partners. At September 30, 2014, these guarantees totaled $18.7 million. At September 30, 2014, WGL's guarantees for all its subsidiaries and external partners totaled $528.5 million. The fair value of these guarantees was insignificant at September 30, 2014.
	Legal Matters
	WGL has been cooperating with a Department of Justice (“the Department”) investigation of some of the federal contracting activities of one of its non-utility subsidiaries, WGESystems. The Department's investigation concerned certain American Recovery and Reinvestment Act projects bid out by the General Services Administration in 2010, in which WGESystems participated as a subcontractor to an 8(a) prime contractor under the Small Business Administration's 8(a) Business Development Program. As discussed in more detail in Note 20 —Subsequent Events, on November 18, 2014, WGESystems entered into a deferred prosecution agreement with the Department, which will resolve the investigation.
	We accrued approximately $2.6 million, representing the fine and monetary penalty to be paid to the Department in connection with this matter, in the fourth quarter of 2014.

Derivative_and_Weather_Related

Derivative and Weather Related Instruments	12 Months Ended
	Sep. 30, 2014
Derivative and Weather-Related Instruments [Abstract]	'
Derivative and Weather-Related Instruments	'
	NOTE 14. DERIVATIVE AND WEATHER-RELATED INSTRUMENTS
	DERIVATIVE INSTRUMENTS
	Regulated Utility Operations
	Washington Gas enters into contracts related to the sale and purchase of natural gas that qualify as derivative instruments and are accounted for under ASC Topic 815. These derivative instruments are recorded at fair value on our balance sheet and Washington Gas does not 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 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 locking in operating margins that Washington Gas will ultimately realize. The derivatives used under this program are subject to mark-to-market accounting treatment while the capacity and transportation resources are not.
	Regulatory sharing mechanisms allow the profit from these transactions to be shared between Washington Gas' shareholders and customers; therefore, any changes in fair value are recorded through earnings, or as regulatory assets or liabilities to the extent that gains and losses associated with these derivative instruments will be included in the rates charged to customers when they are realized. Valuation changes for the portion of net profits to be retained for shareholders may cause significant period-to-period volatility in earnings from unrealized gains and losses. This volatility does not change the locked-in 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 fiscal year ended September 30, 2014 was a net loss of $35.4 million including an unrealized loss of $66.2 million. During the fiscal year ended September 30, 2013 we recorded a net loss of $33.2 million including an unrealized loss of $45.4 million. During the fiscal year ended September 30, 2012 we recorded a net gain of $28.3 million including an unrealized gain of $15.9 million.
	Managing Price Risk. To manage price risk associated with acquiring natural gas supply for utility customers, Washington Gas enters into forward contracts, option contracts, financial contracts and other contracts, as authorized by its regulators. These instruments are accounted for as derivative instruments. 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 utilizes 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 newly issued debt.
	Non-Utility Operations
	Managing Price Risk. WGEServices enters into certain derivative contracts as part of managing the price risk associated with the sale and purchase of natural gas and electricity. WGL Midstream enters into derivative contracts for the purpose of optimizing its storage and transportation capacity as well as managing the transportation and storage assets on behalf of third parties. As the storage and transportation capacities utilized by WGL Midstream are not considered to be derivative instruments, they are not recorded at fair value on our consolidated balance sheets. Washington Gas Resources has warrants to purchase stock from certain of its solar investments that are accounted for as derivative instruments. Derivative instruments are recorded at fair value on our consolidated balance sheets. WGEServices, WGL Midstream and Washington Gas Resources do not designate these derivatives as hedges under ASC Topic 815; therefore, changes in the fair value of these derivative instruments are reflected in the earnings of our non-utility operations and may cause significant period-to-period volatility in earnings.
	Managing Interest-Rate Risk. WGL utilizes derivative instruments that are designed to minimize the risk of interest-rate volatility associated with future debt issuances. During September 2014, WGL entered into interest rate swaps associated with an expected $150 million debt issuance. WGL elected cash flow hedge accounting for its interest rate derivative instruments. Therefore, the effective portion of the gains and losses on the hedge are recorded within other comprehensive income and are expected to be amortized over the life of the debt (through 2044). The amount of ineffectiveness recorded to earnings for the period from the cash flow hedge was $0.2 million.
	Consolidated Operations
	Reflected in the tables below is information for WGL as well as Washington Gas. The information for WGL includes derivative instruments for both utility and non-utility operations.
	At September 30, 2014 and 2013, respectively, the absolute notional amounts of our derivatives are as follows:
	Absolute Notional Amounts
	of Open Positions on Derivative Instruments
	30-Sep-14	Notional Amounts
	Derivative transactions	WGL Holdings			Washington Gas
	Natural Gas (In millions of therms)
	Asset Optimization		20,593.30			13,740.90
	Retail sales		44.7			-
	Other risk-management activities		1,641.30			1,398.20
	Electricity (In millions of kWhs)
	Retail sales		3,831.40			-
	Other risk-management activities		16,734.10			-
	Warrants (In millions of shares)		4.6			-
	Interest Rate Swaps (In millions of dollars)		150			-
	Absolute Notional Amounts
	of Open Positions on Derivative Instruments
	30-Sep-13		Notional Amounts
	Derivative transactions	WGL Holdings			Washington Gas
	Natural Gas (In millions of therms)
	Asset Optimization		13,289.60			11,115.80
	Retail sales		98.9			-
	Other risk-management activities		1,803.60			1,455.70
	Electricity (In millions of kWhs)
	Retail sales		4,790.20			-
	Other risk-management activities		17,647.90			-
	Warrants (In millions of shares)		4.6			-
	Interest Rate Swaps (In millions of dollars)(a)		75			75
	(a)The fair value of our interest rate swaps was minimal at September 30, 2013.
	As of September 30, 2014, the increase in volume of asset optimization related derivatives is primarily the result of new long-term gas purchase contracts for WGL Midstream.
	The following tables present the balance sheet classification for all derivative instruments as of September 30, 2014 and 2013.
	WGL Holdings, Inc.
	Balance Sheet Classification of Derivative Instruments
	(In millions)	Derivative Instruments Not Designated as Hedging Instruments				Derivative Instruments Designated as Hedging Instruments
	As of September 30, 2014	Gross Derivative Assets		Gross Derivative Liabilities		Gross Derivative Assets		Gross Derivative Liabilities		Netting of Collateral		Total(a)
	Current Assets—Derivatives	$	20.8	$	-2.5	$	-	$	-	$	-	$	18.3
	Deferred Charges and Other Assets—Derivatives		18.7		-		-		-		-		18.7
	Current Liabilities—Derivatives		15.4		-70.3		-		-1.7		8		-48.6
	Deferred Credits—Derivatives		17.7		-316.4		-		-		4		-294.7
	Total	$	72.6	$	-389.2	$	-	$	-1.7	$	12	$	-306.3
	As of September 30, 2013
	Current Assets—Derivatives	$	57.3	$	-19.3	$	-	$	-	$	-2.7	$	35.3
	Deferred Charges and Other Assets—Derivatives		57.4		-31.1		-		-		-		26.3
	Accounts Payable and Other Accrued Liabilities		1.5		-		-		-		-		1.5
	Current Liabilities—Derivatives		4.1		-53.4		-		-		0.9		-48.4
	Deferred Credits—Derivatives		-		-144		-		-		2.7		-141.3
	Total	$	120.3	$	-247.8	$	-	$	-	$	0.9	$	-126.6
	Washington Gas Light Company
	Balance Sheet Classification of Derivative Instruments(b)
	(In millions)
As of September 30, 2014	Gross Derivative Assets		Gross Derivative Liabilities		Netting of Collateral		Total(a)
Current Assets—Derivatives	$	3.9	$	-	$	-	$	3.9
Deferred Charges and Other Assets—Derivatives		9.5		-		-		9.5
Current Liabilities—Derivatives		8.6		-43.2		0.7		-33.9
Deferred Credits—Derivatives		4.2		-265.2		0.2		-260.8
Total	$	26.2	$	-308.4	$	0.9	$	-281.3
As of September 30, 2013
Current Assets—Derivatives	$	19.3	$	-12.3	$	-2.7	$	4.3
Deferred Charges and Other Assets—Derivatives		47.2		-31.1		-		16.1
Current Liabilities—Derivatives		1.5		-26.2		-		-24.7
Deferred Credits—Derivatives		-		-106.1		-		-106.1
Total	$	68	$	-175.7	$	-2.7	$	-110.4
(a)WGL 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 815. All recognized derivative contracts and associated financial collateral subject to a master netting arrangement or similar that is eligible for offset under ASC 815 have been presented net in the balance sheet.
(b)Washington Gas did not have any derivative instruments outstanding that were designated as hedging instruments at September 30, 2014, or 2013.
The following tables present all gains and losses associated with derivative instruments for the years ended September 30, 2014, 2013 and 2012.
WGL Holdings, Inc. Gains and Losses on Derivative Instruments
(In millions)
Fiscal Year Ended September 30,		2014		2013		2012
Recorded to income
Operating revenues—non-utility	$	-47.9	$	-9.9	$	19.2
Utility cost of gas		-87.3		-45.9		22.3
Non-utility cost of energy-related sales		36.2		-2.4		-34.2
Other income-net		-1.1		0.2		0.9
Interest expense		-0.2		-		-
Recorded to regulatory assets
Gas costs		-143.3		-115.1		42.2
Other		0.2		-		-
Recorded to other comprehensive income(a)		-1.5		-		-
Total	$	-244.9	$	-173.1	$	50.4
(a)This pre-tax unrealized gain represents the effective portion of our cash flow hedge. Upon settlement of the hedge, the realized gain or loss, to the extent effective, will be amortized as an adjustment to the interest expense. We expect this amortization to be minimal for fiscal 2015.
Washington Gas Gains and Losses on Derivative Instruments
(In millions)
Fiscal Year Ended September 30,		2014		2013		2012
Recorded to income
Utility cost of gas	$	-87.3	$	-45.9	$	22.3
Recorded to regulatory assets
Gas costs		-143.3		-115.1		42.2
Other		0.2		-		-
Total	$	-230.4	$	-161	$	64.5
Collateral
WGL 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 parental 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 WGL's 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. At September 30, 2014, Washington Gas, WGEServices and WGL Midstream posted $8.2 million, $5.7 million and $11.4 million, respectively, of collateral deposits with counterparties that were not offset against open and settled derivative contracts. At September 30, 2013, Washington Gas, WGEServices and WGL Midstream posted $3.0 million, $12.1 million and $8.1 million, respectively, of collateral deposits with counterparties that were not offset against open and settled derivative contracts. In addition, at September 30, 2014 and 2013, Washington Gas held $2.5 million and $4.6 million of cash collateral, respectively, representing an obligation to counterparties that was not offset against open and settled derivative contracts. Any collateral posted that is not offset against open and settled derivative contracts is included in “Other prepayments” in the accompanying balance sheet. Collateral received and not offset against open and settled derivative contracts is included in “Customer deposits and advance payments” in the accompanying balance sheet.
Certain derivative instruments of Washington Gas, WGEServices and WGL Midstream contain contract provisions that require collateral to be posted if the credit rating of Washington Gas or WGL falls below certain levels or if counterparty exposure to WGEServices or WGL Midstream exceeds a certain level. Due to counterparty exposure levels, at September 30, 2014, WGEServices posted $5.3 million of collateral related to its derivative liabilities that contained credit-related contingent features. At September 30, 2013, WGEServices posted $3.6 million of collateral related to these aforementioned derivative liabilities. Washington Gas and WGL Midstream were not required to post any collateral related to its derivative liabilities that contained credit-related contingent features at September 30, 2014 and 2013. 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 September 30, 2014 and 2013, respectively.
Potential Collateral Requirements for Derivative Liabilities
with Credit-risk-Contingent Features
(In millions)	WGL Holdings , Inc.			Washington Gas
30-Sep-14
Derivative liabilities with credit-risk-contingent features	$	28.8		$	20.6
Maximum potential collateral requirements		16.5			16.1
30-Sep-13
Derivative liabilities with credit-risk-contingent features	$	77		$	44.7
Maximum potential collateral requirements		33.6			1.7
Washington Gas, WGEServices and WGL Midstream 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 September 30, 2014, three counterparties each represented over 10% of Washington Gas' credit exposure to wholesale derivative counterparties for a total credit risk of $16.7 million; two counterparties represented over 10% of WGEServices' credit exposure to wholesale derivative counterparties for a total credit risk of $4.1 million; and three counterparties each represented over 10% of WGL Midstream's credit exposure to wholesale counterparties for a total credit risk of $13.6 million.
WEATHER-RELATED INSTRUMENTS
Washington Gas did not use any weather-related instruments during the year ended September 30, 2014. During the fiscal years ended September 30, 2013 and 2012, Washington Gas used HDD weather–related instruments to manage its financial exposure to variations from normal weather in the District of Columbia. Under these contracts, Washington Gas purchased protection against net revenue shortfalls due to warmer-than-normal weather and sold to its counterparty the right to receive the benefit when weather is colder than normal. Washington Gas elected to value all weather-related instruments at fair value.
Gains and losses associated with Washington Gas' weather-related instruments are recorded to “Operation and maintenance” expense. During the years ended September 30, 2013 and 2012, Washington Gas recorded a pre-tax net gain of $0.8 million and $7.9 million respectively, related to weather derivatives.
WGEServices utilizes weather-related instruments for managing the financial effects of weather risks. These instruments cover a portion of WGEServices' estimated revenue or energy-related cost exposure to variations in heating or cooling degree days. These contracts provide for payment to WGEServices of a fixed-dollar amount for every degree day over or under specific levels during the calculation period depending upon the type of contract executed. During the years ended September 30, 2014, 2013 and 2012, WGEServices recorded a pre-tax gain of $3.4 million, a pre-tax loss of $0.8 million and a pre-tax gain of $11.8 million, respectively, related to these instruments.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Sep. 30, 2014
Fair Value Measurements [Abstract]	'
Fair Value Measurements	'
	NOTE 15. FAIR VALUE MEASUREMENTS
	Recurring Basis
	We measure the fair value of our financial assets and liabilities using a combination of the income and market approach in accordance with ASC Topic 820. These financial assets and liabilities primarily consist of (i) derivatives recorded on our balance sheet under ASC Topic 815, (ii) weather-related instruments and (iii) 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 WGL. We value our derivative contracts based on an “in-exchange” premise, and 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. Level 1 assets and liabilities primarily include exchange traded derivatives and securities.
	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 September 30, 2014 and 2013, Level 2 financial assets and liabilities included energy-related derivatives such as financial contracts, options and physical forward contracts for deliveries at active market locations.
	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, annualized volatilities of natural gas prices, and electricity congestion 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 WGL's Chief Financial Officer.  In accordance with WGL's valuation policy, we may utilize a variety of valuation methodologies to fair value 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 September 30, 2014 and 2013, 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 life of the contract; (iii) contracts valued using historical spot price volatility assumptions; (iv) valuations using indicative broker quotes for inactive market locations and (v) non-publicly traded stock warrants.
	The following tables set forth financial instruments recorded at fair value as of September 30, 2014 and 2013, 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.
	WGL Holdings, Inc.
	Fair Value Measurements Under the Fair Value Hierarchy
	(In millions)	Level 1		Level 2		Level 3		Total
	At September 30, 2014
	Assets
	Natural gas related derivatives	$	-	$	22.7	$	33.7	$	56.4
	Electricity related derivatives		-		0.3		15.9		16.2
	Total Assets	$	-	$	23	$	49.6	$	72.6
	Liabilities
	Natural gas related derivatives	$	-	$	-39.8	$	-328.4	$	-368.2
	Electricity related derivatives		-		-0.1		-20.9		-21
	Interest rate derivatives		-		-1.7		-		-1.7
	Total Liabilities	$	-	$	-41.6	$	-349.3	$	-390.9
	At September 30, 2013
	Assets
	Natural gas related derivatives	$	-	$	72.3	$	21.5	$	93.8
	Electricity related derivatives		-		-		25.4		25.4
	Warrants		-		-		1.1		1.1
	Total Assets	$	-	$	72.3	$	48	$	120.3
	Liabilities
	Natural gas related derivatives	$	-	$	-41.1	$	-176.7	$	-217.8
	Electricity related derivatives		-		-7		-23		-30
	Total Liabilities	$	-	$	-48.1	$	-199.7	$	-247.8
	Washington Gas Light Company
	Fair Value Measurements Under the Fair Value Hierarchy
	(In millions)	Level 1		Level 2		Level 3		Total
	At September 30, 2014
	Assets
	Natural gas related derivatives	$	-	$	13.5	$	12.7	$	26.2
	Total Assets	$	-	$	13.5	$	12.7	$	26.2
	Liabilities
	Natural gas related derivatives	$	-	$	-25.1	$	-283.3	$	-308.4
	Total Liabilities	$	-	$	-25.1	$	-283.3	$	-308.4
	At September 30, 2013
	Assets
	Natural gas related derivatives	$	-	$	51	$	17	$	68
	Total Assets	$	-	$	51	$	17	$	68
	Liabilities
	Natural gas related derivatives	$	-	$	-25.1	$	-150.6	$	-175.7
	Total Liabilities	$	-	$	-25.1	$	-150.6	$	-175.7
	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 September 30, 2014 and 2013.
	Quantitative Information about Level 3 Fair Value Measurements
	(In millions)	Net Fair Value September 30, 2014	Valuation Techniques	Unobservable Inputs	Range
	WGL Holdings, Inc.	(In millions)
	Natural gas related derivatives	($294.70)	Discounted Cash Flow	Natural Gas Basis Price (per dekatherm)	($2.101) -	$6.15
			Option Model	Natural Gas Basis Price (per dekatherm)	($1.675) -	$6.15
				Annualized Volatility of Spot Market Natural Gas	30.9% -	589.60%
	Electricity related derivatives	($5.00)	Discounted Cash Flow	Electricity Congestion Price (per megawatt hour)	($2.85) -	$90.95
			Internal Model	Electricity Congestion Price (per megawatt hour)
			Option Model	Electricity Congestion Price (per megawatt hour)
				Annualized Volatility of Electricity Prices
	Washington Gas Light Company
Natural gas related derivatives	($270.60)	Discounted Cash Flow	Natural Gas Basis Price (per dekatherm)	($2.101) -	$6.15
Quantitative Information about Level 3 Fair Value Measurements
(In millions)	Net Fair Value September 30, 2013	Valuation Techniques	Unobservable Inputs	Range
WGL Holdings, Inc.	(In millions)
Natural gas related derivatives	($155.20)	Discounted Cash Flow	Natural Gas Basis Price (per dekatherm)	($1.780) -	$2.21
		Option Model	Natural Gas Basis Price (per dekatherm)	($0.181) -	$0.63
			Annualized Volatility of Spot Market Natural Gas	34.6% -	276.60%
Electricity related derivatives	$2.40	Discounted Cash Flow	Electricity Congestion Price (per megawatt hour)	($1.995) -	$64.15
Washington Gas Light Company
Natural gas related derivatives	($133.60)	Discounted Cash Flow	Natural Gas Basis Price (per dekatherm)	($1.780) -	$2.21
		Option Model	Natural Gas Basis Price (per dekatherm)	$0.024 -	$0.63
			Annualized Volatility of Spot Market Natural Gas	46.8% -	276.60%
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 years ended September 30, 2014 and 2013, respectively.
WGL Holdings, Inc. Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs
(In millions)		Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Fiscal Year Ended September 30, 2014
Balance at October 1, 2013	$	-155.2	$	2.4	$	-	$	1.1	$	-151.7
Realized and unrealized gains (losses)
Recorded to income		-72.6		-5.7		-		-1.1		-79.4
Recorded to regulatory assets - gas costs		-113.6		-		-		-		-113.6
Transfers out of Level 3		1.7		-		-		-		1.7
Purchases		-		5.2		-		-		5.2
Settlements		45		-6.9		-		-		38.1
Balance at September 30, 2014	$	-294.7	$	-5	$	-	$	-	$	-299.7
WGL Holdings, Inc. Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs
(In millions)		Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Fiscal Year Ended September 30, 2013
Balance at October 1, 2012	$	39.6	$	2.8	$	-0.5	$	0.9	$	42.8
Realized and unrealized gains (losses)
Recorded to income		-72.4		-23.8		1.2		0.2		-94.8
Recorded to regulatory assets - gas costs		-115.3		-		-		-		-115.3
Transfers out of Level 3		-17.4		-		-0.7		-		-18.1
Purchases		-		5.7		-		-		5.7
Settlements		10.3		17.7		-		-		28
Balance at September 30, 2013	$	-155.2	$	2.4	$	-	$	1.1	$	-151.7
Washington Gas Light Company Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs
(In millions)		Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Fiscal Year Ended September 30, 2014
Balance at October 1, 2013	$	-133.6	$	-	$	-	$	-	$	-133.6
Realized and unrealized gains (losses)
Recorded to income		-69.4		-		-		-		-69.4
Recorded to regulatory assets - gas costs		-113.6		-		-		-		-113.6
Transfers out of Level 3		1.7		-		-		-		1.7
Settlements		44.3		-		-		-		44.3
Balance at September 30, 2014	$	-270.6	$	-	$	-	$	-	$	-270.6
Washington Gas Light Company Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs
(In millions)		Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Fiscal Year Ended September 30, 2013
Balance at October 1, 2012	$	35.6	$	-	$	-0.5	$	-	$	35.1
Realized and unrealized gains (losses)
Recorded to income		-45.9		-		1.2		-		-44.7
Recorded to regulatory assets - gas costs		-115.3		-		-		-		-115.3
Transfers out of Level 3		-17.4		-		-0.7		-		-18.1
Settlements		9.4		-		-		-		9.4
Balance at September 30, 2013	$	-133.6	$	-	$	-	$	-	$	-133.6
Transfers between different levels of the fair value hierarchy may occur based 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 reporting period. For WGL and Washington Gas net derivative assets transferred out of Level 3 during the fiscal year ended September 30, 2014 reflected an increase in the observable market inputs used to value those instruments.
The table below sets forth the line items on the statements of income to which amounts are recorded for the fiscal years ended September 30, 2014, 2013 and 2012, related to fair value measurements using significant level 3 inputs.
WGL Holdings, Inc. Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements
Fiscal Year Ended September 30, 2014
(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Operating revenues—non-utility	$	-2.3	$	-22.1	$	-	$	-	$	-24.4
Utility cost of gas		-69.4		-		-		-		-69.4
Other income-net		-		-		-		-1.1		-1.1
Non-utility cost of energy-related sales		-0.9		16.4		-		-		15.5
Total	$	-72.6	$	-5.7	$	-	$	-1.1	$	-79.4
WGL Holdings, Inc. Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements
Fiscal Year Ended September 30, 2013
(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Operating revenues—non-utility	$	-27	$	-9.1	$	-	$	-	$	-36.1
Utility cost of gas		-45.8		-		-		-		-45.8
Other income-net		-		-		-		0.2		0.2
Non-utility cost of energy-related sales		0.4		-14.7		-		-		-14.3
Operation and maintenance expense		-		-		1.2		-		1.2
Total	$	-72.4	$	-23.8	$	1.2	$	0.2	$	-94.8
WGL Holdings, Inc. Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements
Fiscal Year Ended September 30, 2012
(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Operating revenues—non-utility	$	3	$	-14.2	$	-	$	-	$	-11.2
Utility cost of gas		14.3		-		-		-		14.3
Other income-net		-		-		-		0.9		0.9
Non-utility cost of energy-related sales		4.8		-33.5		-		-		-28.7
Operation and maintenance expense		-		-		7.9		-		7.9
Total	$	22.1	$	-47.7	$	7.9	$	0.9	$	-16.8
Washington Gas Light Company Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements
Fiscal Year Ended September 30, 2014
(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Utility cost of gas	$	-69.4	$	-	$	-	$	-	$	-69.4
Total	$	-69.4	$	-	$	-	$	-	$	-69.4
Washington Gas Light Company Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements
Fiscal Year Ended September 30, 2013
(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Utility cost of gas	$	-45.9	$	-	$	-	$	-	$	-45.9
Operation and maintenance expense		-		-		1.2		-		1.2
Total	$	-45.9	$	-	$	1.2	$	-	$	-44.7
Washington Gas Light Company Realized and Unrealized Gains (Losses) Recorded for Level 3 Measurements
Fiscal Year Ended September 30, 2012
(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Utility cost of gas	$	14.3	$	-	$	-	$	-	$	14.3
Operation and maintenance expense		-		-		7.9		-		7.9
Total	$	14.3	$	-	$	7.9	$	-	$	22.2
Unrealized gains (losses) for the fiscal years ended September 30, 2014, September 30, 2013 and September 30, 2012 attributable to derivative assets and liabilities measured using significant Level 3 inputs were recorded as follows, respectively:
WGL Holdings, Inc. Unrealized Gains (Losses) Recorded for Level 3 Measurements
Fiscal Year Ended September 30, 2014
(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Recorded to income
Operating revenues—non-utility	$	-5	$	-33.8	$	-	$	-	$	-38.8
Utility cost of gas		-60.6		-		-		-		-60.6
Non-utility cost of energy-related sales		3.7		30		-		-		33.7
Other income-net		-		-		-		-1.1		-1.1
Recorded to regulatory assets—gas costs		-109.9		-		-		-		-109.9
Total	$	-171.8	$	-3.8	$	-	$	-1.1	$	-176.7
WGL Holdings, Inc. Unrealized Gains (Losses) Recorded for Level 3 Measurements
Fiscal Year Ended September 30, 2013
(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Recorded to income
Operating revenues—non-utility	$	-25.3	$	6.6	$	-	$	-	$	-18.7
Utility cost of gas		-44.3		-		-		-		-44.3
Non-utility cost of energy-related sales		0.2		-1.1		-		-		-0.9
Other income-net		-		-		-		0.2		0.2
Recorded to regulatory assets—gas costs		-111.6		-		-		-		-111.6
Total	$	-181	$	5.5	$	-	$	0.2	$	-175.3
WGL Holdings, Inc. Unrealized Gains (Losses) Recorded for Level 3 Measurements
Fiscal Year Ended September 30, 2012
(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Derivatives		Warrants		Total
Recorded to income
Operating revenues—non-utility	$	4.3	$	4.8	$	-	$	-	$	9.1
Utility cost of gas		13.8		-		-		-		13.8
Non-utility cost of energy-related sales		0.8		14		-		-		14.8
Other income-net		-		-		-		0.9		0.9
Operation and maintenance expense		-		-		0.2		-		0.2
Recorded to regulatory assets—gas costs		23.2		-		-		-		23.2
Total	$	42.1	$	18.8	$	0.2	$	0.9	$	62
Washington Gas Light Company Unrealized Gains (Losses) Recorded for Level 3 Measurements
Fiscal Year Ended September 30, 2014
(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Recorded to income
Utility cost of gas	$	-60.6	$	-	$	-	$	-	$	-60.6
Recorded to regulatory assets—gas costs		-109.9		-		-		-		-109.9
Total	$	-170.5	$	-	$	-	$	-	$	-170.5
Washington Gas Light Company Unrealized Gains (Losses) Recorded for Level 3 Measurements
Fiscal Year Ended September 30, 2013
(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Recorded to income
Utility cost of gas	$	-44.3	$	-	$	-	$	-	$	-44.3
Recorded to regulatory assets—gas costs		-111.6		-		-		-		-111.6
Total	$	-155.9	$	-	$	-	$	-	$	-155.9
Washington Gas Light Company Unrealized Gains (Losses) Recorded for Level 3 Measurements
Fiscal Years Ended September 30, 2012
(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
Recorded to income
Utility cost of gas	$	13.8	$	-	$	-	$	-	$	13.8
Operation and maintenance expense		-		-		0.2		-		0.2
Recorded to regulatory assets—gas costs		23.2		-		-		-		23.2
Total	$	37	$	-	$	0.2	$	-	$	37.2
The following table presents the carrying amounts and estimated fair values of our financial instruments at September 30, 2014 and 2013.
WGL Holdings, Inc. Fair Value of Financial Instruments
At September 30,	2014				2013
(In millions)		Carrying Amount		Fair Value		Carrying Amount		Fair Value
Money market funds (a)	$	9.7	$	9.7	$	6.5	$	6.5
Other short- term investments(a)	$	-	$	-	$	0.1	$	0.1
Commercial paper (b)	$	453.5	$	453.5	$	373.1	$	373.1
Long-term debt(c)	$	679.2	$	809.3	$	524.1	$	630.2
Washington Gas Light Company Fair Value of Financial Instruments
At September 30,	2014				2013
(In millions)		Carrying Amount		Fair Value		Carrying Amount		Fair Value
Money market funds (a)	$	4.3	$	4.3	$	3.1	$	3.1
Other short- term investments(a)	$	-	$	-	$	0.1	$	0.1
Commercial paper (b)	$	89	$	89	$	124.5	$	124.5
Long-term debt(c)	$	679.2	$	809.3	$	524.1	$	630.2
(a)Balance located in cash and cash equivalents in the accompanying balance sheets. These amounts may be offset by outstanding checks.
(b)Balance is located in notes payable in the accompanying balance sheets.
(c)Less current maturities and unamortized discounts.
Our money market funds are Level 1 valuations and their carrying amount approximates fair value. Other short-term investments are primarily overnight investment accounts; therefore, their carrying amount approximates fair value based on Level 2 inputs. The maturity of our commercial paper outstanding at both September 30, 2014 and 2013 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. Washington Gas' long-term debt is not actively traded. The fair value of long-term debt was estimated based on the quoted market prices of the U.S. Treasury issues having a similar term to maturity, adjusted for Washington Gas' credit quality. Our long-term debt fair value measurement is classified as Level 3.
Non Recurring Basis
During the fiscal year ended September 30, 2014, Washington Gas recorded an impairment of its previous operations center by reducing the carrying amount of $22.3 million down to its fair value of $21.5 million, resulting in an impairment charge of $0.8 million based on the progress made towards selling the facility. During the fiscal year ended September 30, 2013, Washington Gas recorded an impairment of this facility by reducing the carrying amount of $24.9 million down to its fair value of $22.3 million, resulting in an impairment charge of $2.6 million based on the progress made towards selling the facility. During the fiscal year ended September 30, 2012, Washington Gas recorded an impairment of this facility by reducing the carrying amount of $29.9 million down to its fair value of $24.9 million, resulting in an impairment charge of $5.0 million. The fair value of this facility is a Level 3 measurement. At September 30, 2012, the facility was valued using the discounted cash value model that incorporated the anticipated sale proceeds indicated through a comparable analysis, incorporating expected market trends, and the estimated costs to carry the asset until a sale is completed. The current fiscal year valuation is based on the progress in the efforts to sell the property.
On July 7, 2014, the SCC of VA disallowed full recovery of carrying costs related to an abandoned LNG storage facility. As a result, Washington Gas recorded an impairment charge of $1.9 million. During the fiscal year ended September 30, 2013, Washington Gas recorded an impairment charge of $0.5 million to the abandoned LNG storage facility.

Operating_Segment_Reporting

Operating Segment Reporting	12 Months Ended
	Sep. 30, 2014
Operating Segment Reporting [Abstract]	'
Operating Segment Reporting	'
	NOTE 16. OPERATING SEGMENT REPORTING
	We have four reportable operating segments: regulated utility, retail energy-marketing, commercial energy systems and midstream energy services. The division of these segments into separate revenue generating components is based upon regulation, products and services. Our chief operating decision maker is our Chief Executive Officer. While net income or loss applicable to common stock is the primary criterion for measuring a segment's performance, we also evaluate our operating segments based on other relevant factors, such as penetration into their respective markets and return on equity. Our four segments are summarized below.
	Regulated Utility – The regulated utility segment is our core business. It consists of Washington Gas and Hampshire. Washington Gas provides regulated gas distribution services (including the sale and delivery of natural gas) to customers and natural gas transportation services to an unaffiliated natural gas distribution company in West Virginia under a Federal Energy Regulatory Commission (FERC) approved interstate transportation service operating agreement. Hampshire provides regulated interstate natural gas storage services to Washington Gas under a FERC approved interstate storage service tariff.
	Retail Energy-Marketing – The retail energy-marketing segment consists of WGEServices, which sells natural gas and electricity directly to retail customers in competition with regulated utilities and unregulated gas and electricity marketers.
	Commercial Energy Systems – The commercial energy systems segment consists of WGESystems which provides design-build energy efficient and sustainable solutions including commercial solar, energy efficiency and combined heat and power projects to government and commercial clients. In addition, this segment comprises the operations of WGSW, a holding company formed to invest in alternative energy assets.
	Midstream Energy Services – The midstream energy services segment consists of WGL Midstream, which engages in acquiring, investing in, managing and optimizing natural gas storage and transportation assets.
	Activities and transactions that are not significant enough on a stand-alone basis to warrant treatment as an operating segment, and that do not fit into one of our four operating segments, are aggregated as “Other Activities” and included as part of non-utility operations in the Operating Segment Financial Information presented below. Administrative and business development activity costs associated with the WGL and Washington Gas Resources are included in this segment.
	The following tables present operating segment information for the fiscal years ended September 30, 2014, 2013 and 2012.
	Operating Segment Financial Information
							Non-Utility Operations
	(In thousands)				Regulated Utility		Retail Energy-Marketing	Commercial Energy Systems		Midstream Energy Services		Other Activities		Eliminations(b)		Consolidated
	Year Ended September 30, 2014
	Operating Revenues (a)			$	1,443,800	$	1,310,279	$	40,679	$	16,555	$	-	$	-30,366	$	2,780,947
	Operating Expenses:
		Cost of Energy-Related Sales			726,879		1,238,970		20,348		-		-		-30,613		1,955,584
		Operation			234,391		43,750		10,419		8,517		11,749		75		308,901
		Maintenance			56,972		-		-		-		-		-		56,972
		Depreciation and Amortization			104,064		756		6,178		124		-		-350		110,772
		General Taxes and Other Assessments:
			Revenue Taxes		84,287		8,276		5		-		-		-		92,568
			Other		53,402		4,615		253		274		84		-		58,628
			Total Operating Expenses	$	1,259,995	$	1,296,367	$	37,203	$	8,915	$	11,833	$	-30,888	$	2,583,425
	Operating Income (Loss)				183,805		13,912		3,476		7,640		-11,833		522		197,522
	Equity in Earnings of Unconsolidated Affiliates				-		1		1,953		771		469		-		3,194
	Other Income (Expense)—Net				863		103		1,007		-239		-198		-		1,536
	Interest Expense				37,127		10		-		-		601		-		37,738
	Dividends on Washington Gas Preferred Stock				1,320		-		-		-		-		-		1,320
	Income Tax Expense				48,181		5,764		1,019		1,969		111		210		57,254
	Net Income (Loss) Applicable to Common Stock			$	98,040	$	8,242	$	5,417	$	6,203	$	-12,274	$	312	$	105,940
	Total Assets at September 30, 2014			$	3,979,522	$	389,700	$	521,570	$	211,824	$	369,816	$	-615,933	$	4,856,499
	Capital Expenditures			$	286,323	$	76	$	108,363	$	-	$	-	$	-	$	394,762
	Equity Method Investments at September 30, 2014			$	-	$	-	$	66,810	$	28,076	$	16	$	-	$	94,902
	(a)Operating revenues are reported gross of revenue taxes. Revenue taxes of both the regulated utility and the retail energy-marketing segments include gross receipt taxes. Revenue taxes of the regulated utility segment also include PSC fees, franchise fees and energy taxes. Operating revenue amounts in the "Eliminations" column represent total intersegment revenues associated with sales from the regulated utility segment to the retail energy-marketing segment. Midstream Energy Services' cost of energy related sales is netted with its gross revenues.
	(b)Intersegment eliminations net income includes a timing difference between Commercial Energy Systems' recognition of revenue for the sale of Solar Renewable Energy Credits (SRECs) to Retail Energy-Marketing and Retail Energy's Marketing's recognition of the associate expense. Retail Energy-Marketing has recorded a portion of the SREC's purchased as inventory to be used in future periods at which time they will be expensed.
	Operating Segment Financial Information
							Non-Utility Operations
	(In thousands)				Regulated Utility		Retail Energy-Marketing	Commercial Energy Systems		Midstream Energy Services		Other Activities		Eliminations(b)			Consolidated
	Year Ended September 30, 2013
	Operating Revenues(a)			$	1,200,357	$	1,279,364	$	35,217	$	-20,390	$	-	$	-28,410	$	2,466,138
	Operating Expenses:
		Cost of Energy-Related Sales			521,508		1,164,831		24,450		-		-		-26,458		1,684,331
		Operation			243,341		49,574		6,875		8,683		9,344		-197		317,620
		Maintenance			49,269		-		-		-		-		-		49,269
		Depreciation and Amortization			100,438		726		2,411		124		-		-415		103,284
		General Taxes and Other Assessments:
			Revenue Taxes		81,422		6,831		7		-		-		-		88,260
			Other		52,271		4,411		303		474		97		-		57,556
			Total Operating Expenses	$	1,048,249	$	1,226,373	$	34,046	$	9,281	$	9,441	$	-27,070	$	2,300,320
	Operating Income (Loss)				152,108		52,991		1,171		-29,671		-9,441		-1,340		165,818
	Equity in Earnings of Unconsolidated Affiliates				-		-		1,070		312		128		-		1,510
	Other Income (Expense)—Net				1,539		273		778		-		644		-686		2,548
	Interest Expense				35,631		13		234		417		402		-686		36,011
	Dividends on Washington Gas Preferred Stock				1,320		-		-		-		-		-		1,320
	Income Tax Expense (Benefit)				44,883		20,227		-206		-10,951		-1,124		-537		52,292
	Net Income (Loss) Applicable to Common Stock			$	71,813	$	33,024	$	2,991	$	-18,825	$	-7,947	$	-803	$	80,253
	Total Assets at September 30, 2013			$	3,486,296	$	403,082	$	318,995	$	231,368	$	290,440	$	-470,121	$	4,260,060
	Capital Expenditures			$	227,948	$	730	$	83,667	$	-	$	-	$	-	$	312,345
	Equity Method Investments at September 30, 2013			$	-	$	-	$	54,977	$	6,507	$	413	$	-	$	61,897
	(a)Operating revenues are reported gross of revenue taxes. Revenue taxes of both the regulated utility and the retail energy-marketing segments include gross receipt taxes. Revenue taxes of the regulated utility segment also include PSC fees, franchise fees and energy taxes. Operating revenue amounts in the "Eliminations" column represent total intersegment revenues associated with sales from the regulated utility segment to the retail energy-marketing segment. Midstream Energy Services' cost of energy related sales is netted with its gross revenues.
	(b)Intersegment eliminations net income includes a timing difference between Commercial Energy Systems' recognition of revenue for the sale of Solar Renewable Energy Credits (SRECs) to Retail Energy- Marketing and Retail Energy's Marketing's recognition of the associate expense. Retail Energy- Marketing has recorded a portion of the SREC's purchased as inventory to be used in future periods at which time will be expensed.
	Operating Segment Financial Information
							Non-Utility Operations
	(In thousands)				Regulated Utility		Retail Energy-Marketing	Commercial Energy Systems		Midstream Energy Services		Other Activities		Eliminations(b)			Consolidated
Year Ended September 30, 2012
Operating Revenues			$	1,137,666	$	1,267,070	$	60,325	$	-11,221	$	-	$	-28,530	$	2,425,310
Operating Expenses:
	Cost of Energy-Related Sales			421,539		1,139,162		51,149		-		-		-26,802		1,585,048
	Operation			227,362		52,161		5,414		2,860		3,612		-1,093		290,316
	Maintenance			52,494		-		-		-		-		-		52,494
	Depreciation and Amortization			94,998		735		1,261		116		-		-634		96,476
	General Taxes and Other Assessments:
		Revenue Taxes		74,244		5,776		8		-		-		-		80,028
		Other		50,822		4,070		280		240		16		-1		55,427
		Total Operating Expenses	$	921,459	$	1,201,904	$	58,112	$	3,216	$	3,628	$	-28,530	$	2,159,789
Operating Income (Loss)				216,207		65,166		2,213		-14,437		-3,628		-		265,521
Equity in Earnings of Unconsolidated Affiliates				-		-		947		-		293		-		1,240
Other Income—Net				3,085		42		-32		-		1,097		-38		4,154
Interest Expense				36,098		1		1		-		366		-38		36,428
Dividends on Washington Gas Preferred Stock				1,320		-		-		-		-		-		1,320
Income Tax Expense (Benefit)				72,178		25,876		760		-5,347		-118		-		93,349
Net Income (Loss) Applicable to Common Stock			$	109,696	$	39,331	$	2,367	$	-9,090	$	-2,486	$	-	$	139,818
Total Assets at September 30, 2012			$	3,516,046	$	361,801	$	148,407	$	169,456	$	211,038	$	-295,801	$	4,110,947
Capital Expenditures			$	208,225	$	984	$	41,818	$	101	$	-	$	-	$	251,128
Equity Method Investments at September 30, 2012			$	-	$	-	$	23,346	$	-	$	-	$	-	$	23,346
(a)Operating revenues are reported gross of revenue taxes. Revenue taxes of both the regulated utility and the retail energy-marketing segments include gross receipt taxes. Revenue taxes of the regulated utility segment also include PSC fees, franchise fees and energy taxes. Operating revenue amounts in the "Eliminations" column represent total intersegment revenues associated with sales from the regulated utility segment to the retail energy-marketing segment. Midstream Energy Services' cost of energy related sales is netted with its gross revenues.
(b)Intersegment eliminations net income includes a timing difference between Commercial Energy Systems' recognition of revenue for the sale of Solar Renewable Energy Credits (SRECs) to Retail Energy-Marketing and Retail Energy's Marketing's recognition of the associate expense. Retail Energy-Marketing has recorded a portion of the SREC's purchased as inventory to be used in future periods at which time they will be expensed.

Other_Investments

Other Investments	12 Months Ended
	Sep. 30, 2014
Other Investments [Abstract]	'
Investment [Text Block]	'
	NOTE 17.  OTHER INVESTMENTS
	When determining how to account for our interests in other legal entities, WGL first evaluates if we are required to apply the variable interest entity (VIE) model to the entity, otherwise the entity is evaluated under the voting interest model.
	Under the VIE model, we have a controlling financial interest in a VIE (i.e. are the primary beneficiary) when we have current or potential rights that give us the power to direct the activities of a VIE that most significantly impact the VIE's economic performance combined with a variable interest that gives us the right to receive potentially significant benefits or the obligation to absorb potentially significant losses. When changes occur to the design of an entity we reconsider whether it is subject to the VIE model. We continuously evaluate whether we have a controlling financial interest in a VIE.
	Under the voting interest model, we generally have a controlling financial interest in an entity where we currently hold, directly or indirectly, more than 50% of the voting rights or where we exercise control through substantive participating rights. However, we consider substantive rights held by other partners in determining if we hold a controlling financial interest, and in some cases, despite owning more than 50% of the common stock of an investee, an evaluation of our rights results in the determination that we do not have a controlling financial interest. We reevaluate whether we have a controlling financial interest in these entities when our voting or substantive participating rights change.
	Unconsolidated affiliates are unconsolidated VIEs and other entities evaluated under the voting interest method in which we do not have a controlling financial interest, but over which we have varying degrees of influence. Where we have significant influence, the affiliates are accounted for as equity method investments. Where we do not have significant influence, the affiliates are accounted for under the cost method. Investments in, and advances to, affiliated companies are presented on a one-line basis in the caption “Investments in unconsolidated affiliates” on our Consolidated Balance Sheet.
	WGL uses the Hypothetical Liquidation at Book Value (HLBV) methodology for certain equity method investments when the capital structure of the equity investment results in different liquidation rights and priorities than what is reflected by the underlying percentage ownership interests as defined by an equity investment agreement. For investments accounted for under the HLBV method, simply applying the percentage ownership interest to GAAP net income in order to determine earnings or losses does not accurately represent the income allocation and cash flow distributions that will ultimately be received by the investors. The equity investment agreements for ASD Solar, LP (ASD) and Meade Pipeline Co LLC (Meade) both have liquidation rights and priorities that are sufficiently different from the ownership percentages that the HLBV method was deemed appropriate.
	WGL applies HLBV using a balance sheet approach. A calculation is prepared at each balance sheet date to determine the amount that WGL would receive if an equity investment entity were to liquidate all of its assets (as valued in accordance with GAAP) and distribute that cash to the investors based on the contractually defined liquidation priorities. The difference between the calculated liquidation distribution amounts at the beginning and the end of the reporting period is WGL's share of the earnings or losses from the equity investment for the period. The calculation may vary in its complexity depending on the capital structure and the tax considerations for the investments.
	Variable Interest Entities
	WGL has a variable interest in five investments that qualify as VIEs:
	Meade,
	SunEdison,
	Nextility,
	ASD Solar LP and
	Crab Run.
	WGL and its subsidiaries are not the primary beneficiary for any of the above VIEs, therefore we have not consolidated any of the VIE entities. At September 30, 2014, the nature of WGL's involvement with these investments lacks the characteristics of a controlling financial interest. WGL does not have control over any of the VIEs' activities that are economically significant to the VIEs. In addition, WGL does not have the obligation to absorb expected losses or the right to receive expected gains that could be significant to the VIE.
	Meade
	On February 14, 2014, WGL, through its subsidiary WGL Midstream, entered into a limited liability company agreement and formed Meade, a Delaware limited liability company with COG Holdings LLC, Vega Midstream MPC LLC and River Road Interests LLC. Meade was formed to partner with Transcontinental Gas Pipeline Company, LLC (Williams) to invest in a regulated pipeline project called Central Penn Pipeline (Central Penn). The Central Penn will be an approximately 177 mile pipeline originating in Susquehanna County, Pennsylvania and extending to Lancaster County, Pennsylvania that will have the capacity to transport and deliver up to approximately 1.7 million dekatherms per day of natural gas.
	WGL Midstream plans to invest an estimated $410.0 million for a 55% interest in Meade. WGL Midstream joins COG Holdings LLC (20% share), Vega Midstream MPC LLC (15% share) and River Road Interests LLC (10% share) in Meade. Meade is accounted for under the HLBV equity method of accounting, and any profits and losses are included in “Equity in earnings of unconsolidated affiliates” in the accompanying Consolidated Statement of Income and are added to or subtracted from the carrying amount of WGL's investment balance. WGL Midstream held a $5.8 million equity method investment in Meade at September 30, 2014.
	Our maximum financial exposure includes contributions and guarantees on behalf of WGL Midstream. In addition, we have guaranteed the future commitments of one of the other partners in the venture. Our maximum exposure to loss at September 30, 2014 was $74.0 million, which represents the minimum funding requirements owed to Williams under the Construction and Ownership Agreement should Meade terminate its agreement with Williams early and the guarantee on behalf of one of the other partners.
	SunEdison/Nextility
	WGSW is party to three agreements to fund residential and commercial retail solar energy installations with three separate, privately held companies. WGSW has a master purchase agreement and master lease agreement with SunEdison, Inc. (SunEdison), formerly known as EchoFirst Finance Company LLC (EchoFirst) and Nextility, Inc. (Nextility), formerly known as Skyline Innovations, Inc (Skyline) for sale/leaseback arrangements for residential and commercial solar systems.
	Our agreements with SunEdison and Nextility are accounted for as direct financing leases. WGSW records associated interest in the financing leases in "Other income (expenses)-net" line in the accompanying Consolidated Statement of Income. WGSW held a $19.9 million and $29.2 million combined investment in direct financing leases at September 30, 2014 and 2013, respectively, of which $1.7 million and $5.8 million are current receivables recorded in "Accounts Receivable" in the accompanying Consolidated Balance Sheets at September 30, 2014 and 2013, respectively.
	Minimum future lease payments receivable under direct financing leases over the next five fiscal years and thereafter are as follows:
		Minimum Payments Receivable for Direct Financing Leases
		(In millions)
		2015	$	2.3
		2016		2
		2017		1.9
		2018		1.8
		2019		1.7
		Thereafter		12.3
		Total	$	22
	Minimum payments receivable exclude $5.1 million of residual values and $3.0 million in tax credits. Associated with these investments, WGSW holds $10.2 million of unearned income on its balance sheet. The initial direct costs (incurred in FY 2012) associated with these investments was $0.7million.
	Our maximum financial exposure from solar agreements is limited to its lease payment receivables and investment contributions made to these companies. All additional future committed contributions are contingent on the projects meeting required criteria. Our exposure is offset by the owned physical assets received as part of the transaction and the quick economic return for the investment through the investment tax credit/treasury grant proceeds and accelerated depreciation.
	ASD Solar, LP
	In addition to SunEdison/Skyline, WGSW is also a limited partner in ASD Solar, LP (ASD), a partnership formed to own and operate a portfolio of residential solar projects, primarily rooftop photovoltaic power generation systems. As a limited partner, WGSW provided funding to the partnership but is excluded from involvement in the partnership's operations. In January 2014, the funding commitment period expired for the partnership. WGSW's maximum financial exposure includes contributions made to the partnership.
	Our investment in ASD is accounted for under the HLBV equity method of accounting; any profits and losses are included in “Equity in earnings of unconsolidated affiliates” in the accompanying Consolidated Statement of Income and are added to or subtracted from the carrying amount of WGSW's investment balance. WGSW held a $66.8 million equity method investment in ASD at September 30, 2014.
	ASD is consolidated by the general partner, Solar Direct LLC. Solar Direct LLC is a wholly owned subsidiary of American Solar Direct Inc. (ASDI). At September 30, 2014, the carrying amount of WGSW's investment in ASD exceeded the amount of the underlying equity in net assets by $35.9 million due to WGSW recording additions to its investment in ASD's net assets at fair value of contributions in accordance with GAAP. This basis difference is being amortized over the life of the assets.
	Crab Run
	WGL owns all of the shares of common stock of Crab Run Gas Company. Crab Run Gas Company is an exploration and production company who is the limited partner in the Western/Crab Run Limited Partnership (Crab Run). The partnership was formed to manage oil and gas properties and perform oil and gas leasing, marketing and production activities.
	Crab Run is accounted for under the equity method of accounting; any profits and losses are included in “Equity in earnings of unconsolidated affiliates” in the accompanying Consolidated Statement of Income and are added to or subtracted from the carrying amount of WGL's investment balance. WGL held a minimal portion of equity investment in Crab Run at September 30, 2014.
	Non-VIE Investments
	ASDHI
	Washington Gas Resources held a $5.6 million investment in American Solar Direct Holdings Inc. (ASDHI), at both September 30, 2014 and 2013. This investment is recorded at cost. No identified events or changes in circumstances that may have a significant effect on the carrying value of this investment have occurred. At September 30, 2014 and 2013, Washington Gas Resources also held $0.8 million and $1.9 million, respectively, in warrants of ASDHI which were accounted for as derivatives and recorded at fair value.
	Constitution
	In May of 2013, WGL Midstream invested in Constitution Pipeline Company, LLC (Constitution). WGL Midstream will invest an estimated $72.0 million in the project for a 10% share in the pipeline venture. WGL Midstream joins Williams Partners L.P. (41% share), Cabot Oil and Gas
	Corporation (25% share) and Piedmont Natural Gas (24% share) in the project. This natural gas pipeline venture will transport natural gas per day from the Marcellus region in northern Pennsylvania to major northeastern markets. At September 30, 2014, WGL Midstream had invested $22.2 million. Constitution is accounted for under the equity method of accounting; any profits and losses are included in “Equity in earnings of unconsolidated affiliates” in the accompanying Consolidated Statement of Income and are added to or subtracted from the carrying amount of WGL's investment balance. The equity method is considered appropriate because Constitution is an LLC with specific ownership accounts and ownership between five and fifty percent resulting in WGL Midstream maintaining a more than minor influence over the partnership operating and financing policies.
	The balance sheet location of the investments discussed in this footnote at September 30, 2014 and 2013 are as follows:
	WGL Holdings, Inc Balance Sheet Location of Other Investments
	As of September 30, 2014 (in millions)		VIEs		Non-VIEs		Total
	Assets
	Investments in unconsolidated affiliates	$	72.6	$	27.9	$	100.5
	Investments in direct financing leases, capital leases		18.2		-		18.2
	Accounts receivable		1.7		-		1.7
	Total assets	$	92.5	$	27.9	$	120.4
	WGL Holdings, Inc. Balance Sheet Location of Other Investments
	As of September 30, 2013 (in millions)		VIEs		Non-VIEs		Total
	Assets
	Investments in unconsolidated affiliates	$	55.4	$	12.1	$	67.5
	Investments in direct financing leases, capital leases		23.4		-		23.4
	Deferred charges and other assets- derivatives		-		1.1		1.1
	Accounts receivable		5.8		-		5.8
	Total assets	$	84.6	$	13.2	$	97.8
Liabilities
Other	$	8.5	$	-	$	8.5
Total liabilities	$	8.5	$	-	$	8.5
WGL Holdings, Inc.
Income Statement Location of Other Investments
	Fiscal year ended
	30-Sep-14
(in millions)	VIEs			Non-VIEs	Total
Equity in earnings of unconsolidated affiliates	$	2.2	$	1	$	3.2
Depreciation and amortization	$	0.2	$	-	$	0.2
Other income - net	$	2.6		-		2.6
Net Income	$	4.6	$	1	$	5.6
WGL Holdings, Inc.
Income Statement Location of Other Investments
	Fiscal year ended
	30-Sep-13
(in millions)	VIEs			Non-VIEs	Total
Equity in earnings of unconsolidated affiliates	$	1	$	0.5	$	1.5
Depreciation and amortization		0.1		-		0.1
Other income- net		1.4		-		1.4
Net Income	$	2.3	$	0.5	$	2.8

Related_Party_Transactions

Related Party - Transactions	12 Months Ended
	Sep. 30, 2014
Related Party Transactions [Abstract]	'
Related Party Transactions Disclosure Text Block	'
	NOTE 18. RELATED PARTY TRANSACTIONS
	WGL and its subsidiaries engage in transactions during the ordinary course of business. Inter-company transactions and balances have been eliminated from the consolidated financial statements of WGL, except as described below. Washington Gas provides accounting, treasury, legal and other administrative and general support to affiliates, and files consolidated tax returns that include affiliated taxable transactions. Washington Gas bills its affiliates in accordance with regulatory requirements for the actual cost of providing these services, which approximates their market value. To the extent such billings are not yet paid, 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.
	In connection with billing for unregulated third party marketers 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. The following table presents the receivables and payables from associated companies for the fiscal years ended September 30, 2014 and 2013.
	Washington Gas Light Company
	Receivables / Payables from Associated Companies
	(In millions)	30-Sep-14			30-Sep-13
	Receivables from Associated Companies	$	4.8		$	7.2
	Payables to Associated Companies	$	54.7		$	20.6
	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 WGEServices. Washington Gas records revenues for these balancing services pursuant to tariffs approved by the appropriate regulatory bodies. These related party amounts have been eliminated in the consolidated financial statements of WGL. The following table shows the amounts Washington Gas charged WGEServices for balance services.
	Washington Gas - Gas Balancing Service Charges
			Years Ended September 30,
	(In millions)		2014		2013		2012
	Gas balancing service charge	$	26.6	$	25	$	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. WGEServices recognized an accounts receivable from Washington Gas of $0.02 million and $1.0 million at September 30, 2014 and 2013, respectively, related to an imbalance in gas volumes. Due to regulatory treatment, these receivables and payables are not eliminated in the consolidated financial statements of WGL. Refer to Note 1—Accounting Policies for further discussion of these imbalance transactions.
	Washington Gas participates in a POR program as approved by the PSC of MD, whereby it purchases receivables from participating energy marketers at approved discount rates. In addition, WGEServices participates in POR programs with certain Maryland 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. Any activity between Washington Gas and WGEServices related to the POR program has been eliminated in the accompanying financial statements for WGL. At September 30, 2014 and 2013, Washington Gas had balances of $7.7 million and $106.6 million, respectively, of purchased receivables from WGEServices.

Changes_in_Accumulated_Other_C

Changes in Accumulated Other Comprehensive Income	12 Months Ended
	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Abstract]	'
Changes in Accumulated Other Comprehensive Income by Component [Text Block]	'
	WGL Holdings, Inc.
	Changes in Accumulated Other Comprehensive Income by Component
			September 30,
	(In thousands)		2014		2013
	Beginning Balance	$	-11,048	$	-12,201
	Qualified cash flow hedging instruments(c )		-1,548		-
	Change in prior service cost (credit) (a) (b)		6,095		-1,671
	Amortization of actuarial gain (a)		1,594		3,399
	Amortization of transition obligation (a)		-		238
	Current-period other comprehensive income		6,141		1,966
	Income tax expense related to other comprehensive income (b)		3,054		813
	Ending Balance	$	-7,961	$	-11,048
	(a) These accumulated other comprehensive income components are included in the computation of net periodic benefit cost. Refer to Note 10-Pension and other post-retirement benefit plans for additional details.
	(b) The majority of the 2014 change to the prior service cost component of other comprehensive income is related to the impact of the OPEB plan amendment and re-measurement. Refer to Note 10-Pension and other post-retirement benefit plans for additional details.
	(c ) Cash flow hedging instruments represent interest rate swap agreements on debt issuances. Refer to Note 14 - Derivative and Weather-related Instruments for further discussion of the interest rate swap agreements.
	Washington Gas Light Company
	Changes in Accumulated Other Comprehensive Income by Component
			September 30,
	(In thousands)		2014		2013
	Beginning Balance	$	-11,048	$	-12,201
	Change in prior service cost (credit) (a) (b)		6,095		-1,671
	Amortization of actuarial gain (a)		1,594		3,399
	Amortization of transition obligation (a)		-		238
	Current-period other comprehensive income		7,689		1,966
	Income tax expense related to other comprehensive income (b)		3,054		813
	Ending Balance	$	-6,413	$	-11,048
	(a) These accumulated other comprehensive income components are included in the computation of net periodic benefit cost. Refer to Note 10-Pension and other post-retirement benefit plans for additional details.
	(b) The majority of the 2014 change to the prior service cost component of other comprehensive income is related to the impact of the OPEB plan amendment and re-measurement. Refer to Note 10-Pension and other post-retirement benefit plans for additional details.

Subsequent_Events

Subsequent Events	12 Months Ended
	Sep. 30, 2014
Subsequent Events [Abstract]	'
Subsequent Events [Text Block]	'
	NOTE 20. SUBSEQUENT EVENTS
	Debt Issuances
	On October 24, 2014, WGL issued $100.0 million of 2.25% notes due November 1, 2019 (“2019 Notes”) and $125.0 million of 4.60% notes due November 1, 2044 (“2044 Notes”).  The notes were priced at 99.792% and 99.226% of par, respectively. The first semiannual coupon payment date is May 1, 2015.  These issuances will be recorded at cost.
	The 2019 Notes have a make whole call provision that WGL may exercise at any time on or after October 24, 2014 and prior to October 1, 2019. At any time on or after October 1, 2019, the 2019 Notes may be called at 100% of the principal of such notes, plus accrued and unpaid interest. The 2044 Notes have a make whole call provision that WGL may exercise at any time on or after October 24, 2014 and prior to May 1, 2044. At any time on or after May 1, 2044, the 2044 Notes may be called at 100% of the principal of such notes, plus accrued and unpaid interest.
	In connection with the issuance of the 2044 Notes, WGL settled two forward starting swap hedges for $75.0 million and $50.0 million, both of which resulted in payments to the counterparties of $4.6 million and $3.1 million, respectively.
	Proceeds from the sale of these notes will be used by WGL to primarily fund the repurchase of outstanding securities of WGL and capital investments of its non-utility subsidiaries.
	These transactions were executed with Wells Fargo Securities, LLC, BB&T Capital Markets, TD Securities and CIBC World Markets as underwriters.
	Security Ratings
	On October 15, 2014, Fitch Ratings downgraded WGL's credit rating for its senior unsecured debt to “A” from “A+.” On October 22, 2014, Moody's assigned an issue credit rating for WGL's senior unsecured debt of “A3” and S&P assigned an issue credit rating for WGL's senior unsecured debt of “A.”
	Legal Matters
	As previously disclosed, WGL has been cooperating with a Department of Justice (“the Department”) investigation of some of the federal contracting activities of one of its non-utility subsidiaries, WGESystems. The Department's investigation concerned certain American Recovery and Reinvestment Act projects bid out by the General Services Administration in 2010, in which WGESystems participated as a subcontractor to an 8(a) prime contractor under the Small Business Administration's 8(a) Business Development Program. On November 18, 2014, WGESystems entered into a deferred prosecution agreement with the Department, which will resolve the investigation. The agreement is for a two-year period, and the Department will not pursue the prosecution of WGESystems if WGESystems discharges its obligations under the agreement during the two-year term of the agreement. Pursuant to the agreement, WGESystems will pay fines and monetary penalties totaling $2,587,261 to the Department and implement and maintain certain remedial measures specified in the agreement.

Schedule_II

Schedule II	12 Months Ended
	Sep. 30, 2014
Valuation and Qualifying Accounts [Abstract]	'
Schedule II - Valuation and Qualifying Accounts and Reserves	'
	WGL Holdings, Inc. and Subsidiaries
	Schedule II—Valuation and Qualifying Accounts and Reserves
	Years Ended September 30, 2014, 2013 and 2012
			Balance at		Additions Charged To						Balance
			Beginning		Costs and		Other				at End of
	(In thousands)		of Period		Expenses		Accounts(a)		Deductions(b)		Period
	2014
	Valuation and Qualifying Accounts
	Deducted from Assets in the Balance Sheet:
	Allowance for Doubtful Accounts	$	20,433	$	15,874	$	4,341	$	17,307	$	23,341
	2013
	Valuation and Qualifying Accounts
	Deducted from Assets in the Balance Sheet:
	Allowance for Doubtful Accounts	$	19,792	$	9,527	$	4,217	$	13,103	$	20,433
	2012
	Valuation and Qualifying Accounts
	Deducted from Assets in the Balance Sheet:
	Allowance for Doubtful Accounts	$	17,969	$	18,316	$	4,774	$	21,267	$	19,792
	Notes:
	(a) Recoveries on receivables previously written off as uncollectible and unclaimed customer deposits, overpayments, etc., not refundable.
	(b) Includes deductions for purposes for which reserves were provided or revisions made of estimated exposure.
	Washington Gas Light Company
	Schedule II—Valuation and Qualifying Accounts and Reserves
	Years Ended September 30, 2014, 2013 and 2012
			Balance at		Additions Charged To						Balance at
			Beginning		Costs and		Other				End of
	(In thousands)		of Period		Expenses		Accounts(a)		Deductions(b)		Period
	2014
	Valuation and Qualifying Accounts
	Deducted from Assets in the Balance Sheet:
	Allowance for Doubtful Accounts	$	17,498	$	12,004	$	4,198	$	14,491	$	19,209
	2013
	Valuation and Qualifying Accounts
	Deducted from Assets in the Balance Sheet:
	Allowance for Doubtful Accounts	$	17,129	$	7,024	$	3,978	$	10,633	$	17,498
	2012
	Valuation and Qualifying Accounts
	Deducted from Assets in the Balance Sheet:
	Allowance for Doubtful Accounts	$	15,863	$	12,794	$	4,300	$	15,828	$	17,129
	Notes:
	(a) Recoveries on receivables previously written off as uncollectible and unclaimed customer deposits, overpayments, etc., not refundable.
	(b) Includes deductions for purposes for which reserves were provided or revisions made of estimated exposure.

Quarterly_Financial_Informatio

Quarterly Financial Information	12 Months Ended
	Sep. 30, 2014
Quarterly Financial Information Disclosure [Abstract]	'
Quarterly Financial Information [Text Block]	'
	SUPPLEMENTARY FINANCIAL INFORMATION (Unaudited)
	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.
	##XSQuarter Ended
	(In thousands, except per share data)	December 31			March 31		June 30	30-Sep
	Fiscal Year 2014
	WGL Holdings, Inc.
	Operating revenues	$	680,297	$	1,174,250	$	467,500	$	458,900
	Operating income (loss)	$	32,712	$	104,733	$	-9,489	$	69,566
	Net income (loss) applicable to common stock	$	18,629	$	61,213	$	-11,940	$	38,038
	Earnings (loss) per average share of common stock:
	Basic	$	0.36	$	1.18	$	-0.23	$	0.74
	Diluted	$	0.36	$	1.18	$	-0.23	$	0.74
	Washington Gas Light Company
	Operating revenues	$	390,415	$	716,808	$	197,752	$	138,825
	Operating income	$	65,229	$	88,038	$	4,326	$	24,530
	Net income (loss) applicable to common stock	$	38,477	$	49,176	$	-521	$	9,872
	Fiscal Year 2013
	WGL Holdings, Inc.
	Operating revenues	$	686,736	$	891,383	$	478,118	$	409,901
	Operating income (loss)	$	94,616	$	155,584	$	-9,111	$	-75,270
	Net income (loss) applicable to common stock	$	52,388	$	89,505	$	-10,015	$	-51,625
	Earnings (loss) per average share of common stock:
	Basic	$	1.01	$	1.73	$	-0.19	$	-1
	Diluted	$	1.01	$	1.73	$	-0.19	$	-1
	Washington Gas Light Company
	Operating revenues	$	355,817	$	535,950	$	180,882	$	127,708
	Operating income (loss)	$	72,037	$	134,358	$	-368	$	-55,421
	Net income (loss) applicable to common stock	$	38,387	$	76,935	$	-4,531	$	-39,789
	During the first quarter of fiscal year 2014, Washington Gas recorded an impairment charge of $0.8 million related to the Springfield Operations Center. During the third quarter of fiscal year 2014, Washington Gas recorded a $1.9 million impairment charge on a proposed LNG storage facility. During the fourth quarter of fiscal year 2013, Washington Gas recorded an impairment charge of $2.6 million related to the Springfield Operations Center and a $0.5 million impairment charge on a proposed LNG storage facility. Refer to Note 1 - Accounting Policies of the Notes to Consolidated Financial Statements for further discussion of the impairments.

Accounting_Policies_Policies

Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2014
Organization And Significant Accounting Policies [Abstract]	'
Consolidation, Policy [Policy Text Block]	'
	CONSOLIDATION OF FINANCIAL STATEMENTS
	The consolidated financial statements include the accounts of WGL and its subsidiaries during the fiscal years reported. Certain prior period amounts have been recast to conform to current period presentation. Inter-company transactions have been eliminated. Refer to Note 18—Related Party Transactions for a discussion of inter-company transactions. WGL has a variable interest in five investments that qualify as variable interest entities (VIEs). At September 30, 2014, WGL and its subsidiaries are not the primary beneficiary for any of the VIEs, therefore we have not consolidated any of the VIE entities. Our other investment projects are recorded using the cost method and as direct financing leases. Refer to Note 17—Other Investments for a discussion of VIEs and other investments.
Use of Estimates, Policy [Policy Text Block]	'
	USE OF ESTIMATES IN THE PREPARATION OF FINANCIAL STATEMENTS
	In accordance with generally accepted accounting principles in the United States of America (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, Policy [Policy Text Block]	'
	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. Washington Gas capitalizes AFUDC as a component of construction overhead. The before-tax rates for AFUDC for fiscal years September 30, 2014, 2013 and 2012 were 3.36%, 5.43% and 7.40%, respectively.
	Washington Gas charges maintenance and repairs directly to operating expenses, except those charges applicable to transportation and power-operated equipment, which it allocates to operating expenses, construction and other accounts based on the use of the equipment. 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 depreciation and amortization rate of the regulated utility segment was 2.77%, 2.86% and 2.87% during fiscal years 2014, 2013 and 2012, 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 Obligatons".
	At September 30, 2014 and 2013, 93.6% and 95.6%, respectively, of WGL's consolidated original cost of property, plant and equipment was related to the regulated utility segment as shown below.
Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block]	'
	IMPAIRMENT OF LONG-LIVED ASSETS
	Management regularly reviews property and equipment and other long-lived assets, including certain definite-lived intangible assets and our equity method investments for possible impairment. This review occurs quarterly, or more frequently if events or changes in circumstances indicate the carrying amount of the asset may not be recoverable.
	During September 30, 2014, 2013 and 2012, Washington Gas recorded impairment charges of $0.8 million, $2.6 million and $5.0 million, respectively, in operation and maintenance expense related to its Springfield Operations Center asset. Washington Gas is actively marketing the unused operations facility for sale. At September 30, 2014 and 2013, Washington Gas recorded a $1.9 million and $0.5 million impairment loss for the unrecoverable portion of the costs incurred associated with an abandoned LNG storage project.
	For our equity and cost method investments, an impairment is recorded when the investment has experienced decline in value that is other-than-temporary. Additionally, if the projects in which we hold an investment recognize an impairment loss, we would record our proportionate share of that impairment loss and evaluate the investment for decline in value that is other-than-temporary. There were no events or circumstances during the years ended September 30, 2014, 2013 and 2012 that resulted in any impairment charges.
Lease, Policy [Policy Text Block]	'
	OPERATING LEASES
	We have classified the lease of our corporate headquarters as an operating lease. 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 lease. For this purpose, the lease term began on the date when the lessor commenced constructing the leasehold improvements which allowed us to occupy our corporate headquarters. 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 15-year non-cancelable period of the lease. Refer to Note 13—Commitments and Contingencies for financial data for all of our operating leases.
	DIRECT FINANCING LEASES
	WGSW is party to three agreements to fund residential and commercial retail solar energy installations with three separate, privately held companies. WGSW has a master purchase agreement and master lease agreement with SunEdison, Inc. (SunEdison), formerly known as EchoFirst Finance Company LLC (EchoFirst) and Nextility, Inc. (Nextility), formerly known as Skyline Innovations, Inc (Skyline) for sale/leaseback arrangements for residential and commercial solar systems. Our agreements with SunEdison and Nextility are accounted for as direct financing leases. WGSW records associated interest in the financing leases in "Other income (expenses)-net" line in the accompanying Consolidated Statement of Income.
Cash and Cash Equivalents, Policy [Policy Text Block]	'
	CASH AND CASH EQUIVALENTS
	We consider all investments with original maturities of three months or less to be cash equivalents. We did not have any restrictions on our cash balances that would impact the payment of dividends by WGL or our subsidiaries as of September 30, 2014 and 2013.
Storage Gas Valutation Methods	'
	STORAGE GAS VALUATION METHODS
	For Washington Gas and WGEServices, storage gas inventory is stated at the lower-of-cost or market as determined using the first-in, first-out method. For WGL Midstream, storage gas inventory is stated at the lower-of-cost or market using the weighted average cost method.
	For the fiscal year ended September 30, 2014, Washington Gas recorded a decrease to net income due to a lower-of-cost or market adjustment of $0.2 million. For the fiscal year ended September 30, 2013, Washington Gas did not record any lower-of-cost or market adjustments. For the fiscal year ended September 30, 2012, Washington Gas recorded a decrease to net income due to a lower-of-cost or market adjustment of $1.4 million. For the fiscal years ended September 30, 2014, 2013 and 2012, WGEServices did not record any lower-of-cost or market adjustments. For the fiscal years ended September 30, 2014, 2013 and 2012, WGL Midstream recorded a decrease to net income due to lower-of-cost or market adjustments of $3.0 million, $10.1 million and $22.4 million, respectively.
Derivatives, Reporting of Derivative Activity [Policy Text Block]	'
	WEATHER-RELATED INSTRUMENTS
	Periodically, we purchase certain weather-related instruments, such as HDD derivatives and CDD derivatives. We account for these weather related instruments in accordance with Financial Accounting Standards Board Accounting Standards Codification (ASC) Subtopic 815-45, Derivatives and Hedging—Weather Derivatives. For weather insurance policies and HDD derivatives, benefits or costs are ultimately recognized to the extent actual HDDs fall above or below the contractual HDDs for each instrument. Benefits or costs are recognized for CDD derivatives when the average temperature exceeds a contractually stated level during the contract period. Premiums for weather-related instruments are amortized based on the pattern of normal temperature days over the coverage period. Weather-related instruments for which we collect a premium are carried at fair value. Washington Gas' weather related instrument premium expense or benefit is not considered in establishing retail rates. Washington Gas does not purchase such instruments for jurisdictions in which it has received rate mechanisms that compensate it on a normal weather basis. Refer to Note 14—Derivative and Weather-Related Instruments for further discussion of our weather-related instruments.
	DERIVATIVE ACTIVITIES
	Regulated Utility. 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 recoverable or refundable to customers and therefore subject to ASC Topic 980, Regulated Operations, 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 locking in operating margins that Washington Gas expects to ultimately realize. The 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 volatility will not change the margins that Washington Gas expects to realize from these transactions. 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 Medium-Term Notes (MTNs). 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 14—Derivative and Weather-Related Instruments for further discussion of our derivative activities.
	Non-Utility Operations. WGEServices enters into both physical and financial contracts for the purchase and sale of natural gas and electricity. We designate a portion of these physical contracts related to the purchase of natural gas and electricity to serve our customers as “normal purchases and normal sales;” therefore, they are not subject to the mark-to-market accounting requirements of ASC Topic 815. WGL Midstream enters into derivative contracts for the purpose of optimizing its storage and transportation capacity as well as managing the transportation and storage assets on behalf of third parties. The financial contracts and the portion of the physical contracts that qualify as derivative instruments and are subject to the mark-to-market accounting requirements are recorded on the balance sheet at fair value and are reflected in earnings. WGEServices records these derivatives as revenues or expenses depending on the nature of the economically hedged item. WGL Midstream nets financial and physical contracts in revenues. WGL may, from time to time, designate interest rate swaps used to manage the interest rate risk associated with future debt issuances, as cash flow hedges. Any gains or losses arising from the effective portion of cash flow hedges are recorded in other comprehensive income and are amortized using the effective interest rate method into earnings over the same period as the hedged interest payments are made.  Gains or losses arising from the ineffective portion of cash flow hedges are recognized in earnings immediately.
Income Tax, Policy [Policy Text Block]	'
	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, including those where regulators prohibit deferred income tax treatment 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. Refer to Note 2— Regulated Operations for Washington Gas' regulatory assets and liabilities associated with income taxes due from and to customers at September 30, 2014 and 2013. Amounts applicable to income taxes due from and due to customers primarily represent differences between the book and tax basis of net utility plant in service. We amortize investment tax credits as reductions to income tax expense over the estimated service lives of the related properties. Refer to Note 9—Income Taxes which provides detailed financial information related to our income taxes.
Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]	'
	STOCK-BASED COMPENSATION
	We account for stock-based compensation expense in accordance with ASC Topic 718, Compensation—Stock Compensation, which requires us to measure and recognize stock-based compensation expense in our financial statements based on the fair value at the date of grant for our equity-classified share-based awards, which include performance shares and stock options granted to certain employees and shares issued to directors. For liability-classified share-based awards, which include performance units, we recognize stock-based compensation expense based on their fair value at the end of each reporting period. For both equity-classified and liability-classified share-based awards, 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 11—Stock-Based Compensation for further discussion of the accounting for our stock-based compensation plans.
Asset Retirement Obligations, Policy [Policy Text Block]	'
	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 asset retirement obligations include the costs to cut, purge and cap distribution system, remove asbestos 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.
Fair Value Measurement Policy [Policy Text Block]	'
	Recurring Basis
	We measure the fair value of our financial assets and liabilities using a combination of the income and market approach in accordance with ASC Topic 820. These financial assets and liabilities primarily consist of (i) derivatives recorded on our balance sheet under ASC Topic 815, (ii) weather-related instruments and (iii) 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 WGL. We value our derivative contracts based on an “in-exchange” premise, and 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.
Investment [Policy Text Block]	'When determining how to account for our interests in other legal entities, WGL first evaluates if we are required to apply the variable interest entity (VIE) model to the entity, otherwise the entity is evaluated under the voting interest model.
	Variable Interest Entities
	Meade is accounted for under the HLBV equity method of accounting, and any profits and losses are included in “Equity in earnings of unconsolidated affiliates” in the accompanying Consolidated Statement of Income and are added to or subtracted from the carrying amount of WGL's investment balance.
	Our investment in ASD is accounted for under the HLBV equity method of accounting; any profits and losses are included in “Equity in earnings of unconsolidated affiliates” in the accompanying Consolidated Statement of Income and are added to or subtracted from the carrying amount of WGSW's investment balance.
	Crab Run is accounted for under the equity method of accounting; any profits and losses are included in “Equity in earnings of unconsolidated affiliates” in the accompanying Consolidated Statement of Income and are added to or subtracted from the carrying amount of WGL's investment balance.
	Non Variable Interest Entities
	Washington Gas Resources holds an investment in American Solar Direct Holdings Inc. (ASDHI). This investment is recorded at cost. No identified events or changes in circumstances that may have a significant effect on the carrying value of this investment have occurred.
	Constitution is accounted for under the equity method of accounting; any profits and losses are included in “Equity in earnings of unconsolidated affiliates” in the accompanying Consolidated Statement of Income and are added to or subtracted from the carrying amount of WGL's investment balance. The equity method is considered appropriate because Constitution is an LLC with specific ownership accounts and ownership between five and fifty percent resulting in WGL Midstream maintaining a more than minor influence over the partnership operating and financing policies.
	Refer to Note 17 - Other Investments for further discussion of our investments.
	OTHER INVESTMENTS
Regulatory Assets and Liabilities Recognition Criteria	'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 shareholders. 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 or, in the case of amounts to be shared with rate payers, regulatory liabilities. 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 WGEServices, into a single “net” adjustment to the regulatory asset or liability. Refer to Note 18—Related Party Transactions for further discussion of the accounting for these imbalance transactions. 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. RATE REFUNDS DUE TO CUSTOMERS When Washington Gas files a request with certain regulatory commissions to modify customers’ rates, it is 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 13—Commitments and Contingencies for further discussion of regulatory matters and related contingencies.
Revenue Recognition Policy	'
	REVENUE AND COST RECOGNITION
	Regulated Utility Operations
	Revenues.  For regulated deliveries of natural gas, Washington Gas reads meters and bills customers on a 21 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.
	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. Refer to Note 16—Operating Segment Reporting for amounts recorded related to revenue taxes.
	Non-Utility Operations
	Retail Energy-Marketing Segment.  WGEServices sells natural gas and electricity on an unregulated basis to residential, commercial and industrial customers both inside and outside the Washington Gas service territory.
	WGEServices enters into indexed or fixed-rate contracts with residential, commercial and industrial customers for sales of natural gas and electricity. Customer contracts, which typically have terms less than 24 months, but may extend up to five years, allow WGEServices to bill customers based upon metered gas and electricity usage. Usage is measured either on a cycle basis at customer premises or based on quantities delivered to the local utility, both of which may vary by month. The billing cycles for customers do not coincide with the accounting periods used for financial reporting purposes; therefore, WGEServices accrues unbilled revenues for gas and electricity delivered, but not yet billed, at the end of each accounting period. Revenues are reflected in “Operating Revenues—Non utility.”
	WGEServices procures natural gas and electricity supply under contract structures in which it assembles the various components of supply from multiple suppliers to match its customer requirements. The cost of natural gas and electricity for these purchases is recorded using the contracted volumes and prices in “Non-Utility cost of energy-related sales.”
	Commercial Energy Systems Segment.  WGESystems recognizes income and expenses for all design-build construction contracts using the percentage-of-completion method in “Operating Revenues—Non-utility” and “Non-Utility cost of energy-related sales.” WGESystems also recognizes income from its distributed energy assets based on the terms of the related power purchase agreements. Solar Renewable Energy Certificates (SRECs) are recorded as inventory by WGESystems after every 1,000 Kilowatt-hours (kwh) of electricity are produced by an eligible solar facility. WGESystems recognizes income on the sale of SRECs based on the contractual terms and conditions of the sale. WGSW recognizes income on its investments in distributed energy assets based on the specific terms of its sale leaseback arrangements and through the hypothetical liquidation at book value approach to the equity method of investment accounting for its investment interest. Other income and expense is recognized from the lease of distributed energy assets associated with the SunEdison and Nextility associations.
	Midstream Energy Services Segment.  WGL Midstream reports its margins in non-utility revenue by netting its cost / loss on physical and financial gas purchase contracts with revenues / gains on physical and financial gas sales contracts.
	Other Activities. Washington Gas Resources recognizes income on its investment using the cost approach of investment accounting. Crab Run recognizes income using the equity method of accounting.

Accounting_Policies_Tables

Accounting Policies (Tables)	12 Months Ended
	Sep. 30, 2014
Public Utilities, Property, Plant and Equipment [Abstract]	'
Schedule of Public Utility Property, Plant, and Equipment [Table Text Block]	'
	Property, Plant and Equipment at Original Cost
	September 30,		2014			2013
	($ In millions)		Dollars	%		Dollars	%
	Regulated utility segment
	Distribution, transmission and storage	$	3,635.30	79.3	$	3,356.10	81.5
	General, miscellaneous and intangibles		448.3	9.8		430.6	10.4
	Construction work in progress (CWIP)		203.9	4.5		150.8	3.7
	Total regulated utility segment		4,287.50	93.6		3,937.50	95.6
	Unregulated segments		295.3	6.4		180.6	4.4
	Total	$	4,582.80	100	$	4,118.10	100
WGL Holdings, Inc.	'
Changes in Asset Retirement Obligations [Line Items]	'
Schedule of Change in Asset Retirement Obligation [Table Text Block]	'
		WGL Holdings, Inc.
		Changes in Asset Retirement Obligations
				September 30,
		(In millions)		2014		2013
		Asset retirement obligations at beginning of year	$	104	$	72.7
		Liabilities incurred in the period		4.9		1.2
		Liabilities settled in the period		-5.2		-1
		Accretion expense		4.4		3.3
		Revisions in estimated cash flows(a)		73.1		27.8
		Asset retirement obligations at the end of the year(b)	$	181.2	$	104
Washington Gas Light Company	'
Changes in Asset Retirement Obligations [Line Items]	'
Schedule of Change in Asset Retirement Obligation [Table Text Block]	'
		Washington Gas Light Company
		Changes in Asset Retirement Obligations
				September 30,
		(In millions)		2014		2013
		Asset retirement obligations at beginning of year	$	102.7	$	71.5
		Liabilities incurred in the period		4.9		1.1
		Liabilities settled in the period		-5.2		-1
		Accretion expense		4.3		3.3
		Revisions in estimated cash flows(a)		73.1		27.8
		Asset retirement obligations at the end of the year(b)	$	179.8	$	102.7
		(a) WGL revised its assumptions regarding the timing and amounts related to its obligation to cut, cap and purge pipeline. The revision is primarily driven by our accelerated pipeline replacement programs.
		(b) Includes short-term asset retirement obligations of $6.0 million and $2.7 million for fiscal year 2014 and 2013, respectively.

Regulated_Operations_Table

Regulated Operations (Table)	12 Months Ended
	Sep. 30, 2014
Regulatory Assets and Liabilities Disclosure [Abstract]	'
Schedule of Regulatory Assets and Liabilities [Text Block]	'
	Regulatory Assets and Liabilities
			Regulatory				Regulatory
	(In millions)		Assets				Liabilities
	September 30,		2014		2013		2014		2013
	Current:
	Gas costs due from/to customers(a)	$	-	$	-	$	16.2	$	23.4
	Interruptible sharing(a)		3.4		10.7		-		1.9
	Revenue normalization mechanisms for Maryland and Virginia(a)		-		0.1		5.5		1.5
	Plant recovery mechanisms		0.4		-		0.9		0.2
	Total current	$	3.8	$	10.8	$	22.6	$	27
	Deferred:
	Accrued asset removal costs	$	-	$	-	$	327.4	$	321.3
	Deferred gas costs(a)		191.3		94		-		-
	Pension and other post-retirement benefits
	Other post-retirement benefit costs—trackers(b)		-		0.7		-		-
	Deferred pension costs/income—trackers(b)		45.1		51		-		-
	ASC Topic 715 unrecognized costs/income(a)(c)
	Pensions		147.9		155.1		-		-
	Other post-retirement benefits		-		33.8		86.4		-
	Total pension and other post-retirement benefits		193		240.6		86.4		-
	Other
	Income tax-related amounts due from/to customers(d)		30.4		24.9		4.8		4.5
	Losses/gains on issuance and extinguishments of
	debt and interest-rate derivative instruments(a)(e)		12		11.6		1.7		0.6
	Deferred gain on sale of assets(a)		-		-		1.4		1.7
	Rights-of-way fees(a)		1.5		-		-		1.6
	Other costs—Business process outsourcing (a)		1		1.4		-		-
	Nonretirement postemployment benefits(a)(f)		16.3		15.4		-		-
	Deferred integrity management expenditures(a)(g)		2.7		-		-		-
	Recoverable portion of abandoned LNG facility(a)		5.6		7.9		-		-
	Other regulatory expenses(a)		2.1		4.8		9.7		5.1
	Total other	$	71.6	$	66	$	17.6	$	13.5
	Total deferred	$	455.9	$	400.6	$	431.4	$	334.8
	Total	$	459.7	$	411.4	$	454	$	361.8
	(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) Relates to the District of Columbia jurisdiction.
	(c) Refer to Note 10-Pension and Other Post-Retirement Benefit Plans for a further discussion of these amounts.
	(d) 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.
	(e) 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.
	(f) 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.
	(g)This balance represents amounts for deferred expenditures associated with Washington Gas' Distribution Integrity Management Program (DIMP) in Virginia.

Accounts_Payable_and_Other_Acc1

Accounts Payable and Other Accrued Liabilities (Tables)	12 Months Ended
	Sep. 30, 2014
WGL Holdings, Inc.	'
Accounts Payable and Other Accrued Liabilities	'
		WGL Holdings, Inc.
				September 30,
		(In millions)		2014		2013
		Accounts payable—trade	$	278.8	$	216.3
		Employee benefits and payroll accruals		19.8		23.4
		Embedded derivatives and other accrued liabilities		14.6		30.9
		Total	$	313.2	$	270.6
Washington Gas Light Company	'
Accounts Payable and Other Accrued Liabilities	'
		Washington Gas Light Company
				September 30,
		(In millions)		2014		2013
		Accounts payable—trade	$	146.4	$	99.7
		Employee benefits and payroll accruals		18.2		21.4
		Embedded derivatives and other accrued liabilities		11.9		11.7
		Total	$	176.5	$	132.8

ShortTerm_Debt_Tables

Short-Term Debt (Tables)	12 Months Ended
	Sep. 30, 2014
Short Term Debt Tables [Abstract]	'
Commited Credit Available	'
	Committed Credit Available (In millions)
	30-Sep-14	WGL Holdings, Inc.(b)		Washington Gas		Total Consolidated
	Committed credit agreements
	Unsecured revolving credit facility, expires April 3, 2017(a)	$	450	$	350	$	800
	Less: Commercial Paper		-364.5		-89		-453.5
	Net committed credit available	$	85.5	$	261	$	346.5
	Weighted average interest rate		0.20%		0.13%		0.19%
	30-Sep-13
	Committed credit agreements
	Unsecured revolving credit facility, expires April 3, 2017(a)	$	450	$	350	$	800
	Less: Commercial Paper		-248.6		-124.5		-373.1
	Net committed credit available	$	201.4	$	225.5	$	426.9
	Weighted average interest rate		0.21%		0.13%		0.19%
	(a)Both WGL and Washington Gas have the right to request extensions with the banks’ approval. WGL’s revolving credit facility permits it to borrow an additional $100 million, with the banks’ approval, for a total of $550 million. Washington Gas’ revolving credit facility permits it to borrow an additional $100 million, with the banks’ approval, for a total of $450 million.
	(b)WGL Holdings includes all subsidiaries other than Washington Gas Light Company.

Long_Term_Debt_Tables

Long Term Debt (Tables)	12 Months Ended
	Sep. 30, 2014
Long Term Debt Tables [Abstract]	'
MTN and Private Placement Issuances and Retirements	'
		MTN and Private Placement Issuances and Retirements
		($ In millions)	Principal			Interest Rate	Nominal Maturity Date
		Year Ended September 30, 2014
		Issuances:
		12/5/13	$	75		5.00%(a)	12/15/43
		9/12/14		100		4.22%(b)	9/15/44
		Total	$	175
		Retirements:
		11/7/13	$	37		4.88%	11/7/13
		9/10/14		30		5.17%	9/10/14
		Total	$	67
		(a)The estimated effective cost of the issued notes, including consideration of issuances fees and hedge costs, is 4.95%.
		(b)The estimated effective cost of the issued notes, including consideration of issuances fees and hedge costs, is 4.27%.
Long Term Debt Maturities	'
		Long-Term Debt Maturities(a)
		(In millions)	MTNs		Other		Total
		2015	$	20	$	-	$	20
		2016		25		-		25
		2017		-		-		-
		2018		-		-		-
		2019		50		-		50
		Thereafter		596		-		596
		Total (before project debt financing)	$	691	$	-	$	691
		Project debt financing(b)		-		8.3		8.3
		Total	$	691	$	8.3	$	699.3
		Less: current maturities		20		-		20
		Total non-current	$	671	$	8.3	$	679.3
		(a)Excludes unamortized discounts of $121,567 at September 30, 2014.
		(b)Project debt financing is anticipated to be a non-cash extinguishment. Refer to Note 13 - Commitments and Contingencies for further discussion of this construction project financing.

Derivative_and_Weather_Related1

Derivative and Weather Related Instruments (Tables)	12 Months Ended
	Sep. 30, 2014
Absolute Notional Amounts of Open Positions on Derivative Instruments	'
	Absolute Notional Amounts
	of Open Positions on Derivative Instruments
	30-Sep-14	Notional Amounts
	Derivative transactions	WGL Holdings			Washington Gas
	Natural Gas (In millions of therms)
	Asset Optimization		20,593.30			13,740.90
	Retail sales		44.7			-
	Other risk-management activities		1,641.30			1,398.20
	Electricity (In millions of kWhs)
	Retail sales		3,831.40			-
	Other risk-management activities		16,734.10			-
	Warrants (In millions of shares)		4.6			-
	Interest Rate Swaps (In millions of dollars)		150			-
	Absolute Notional Amounts
	of Open Positions on Derivative Instruments
	30-Sep-13		Notional Amounts
	Derivative transactions	WGL Holdings			Washington Gas
	Natural Gas (In millions of therms)
	Asset Optimization		13,289.60			11,115.80
	Retail sales		98.9			-
	Other risk-management activities		1,803.60			1,455.70
	Electricity (In millions of kWhs)
	Retail sales		4,790.20			-
	Other risk-management activities		17,647.90			-
	Warrants (In millions of shares)		4.6			-
	Interest Rate Swaps (In millions of dollars)(a)		75			75
	(a)The fair value of our interest rate swaps was minimal at September 30, 2013.
Potential Collateral Requirements for Derivative Liabilities with Credit-risk-Contingent Features	'
	Potential Collateral Requirements for Derivative Liabilities
	with Credit-risk-Contingent Features
	(In millions)	WGL Holdings , Inc.			Washington Gas
	30-Sep-14
	Derivative liabilities with credit-risk-contingent features	$	28.8		$	20.6
	Maximum potential collateral requirements		16.5			16.1
	30-Sep-13
	Derivative liabilities with credit-risk-contingent features	$	77		$	44.7
	Maximum potential collateral requirements		33.6			1.7
WGL Holdings, Inc.	'
Balance Sheet Classification of Derivative Instruments	'
	WGL Holdings, Inc.
	Balance Sheet Classification of Derivative Instruments
	(In millions)	Derivative Instruments Not Designated as Hedging Instruments				Derivative Instruments Designated as Hedging Instruments
	As of September 30, 2014	Gross Derivative Assets		Gross Derivative Liabilities		Gross Derivative Assets		Gross Derivative Liabilities		Netting of Collateral		Total(a)
	Current Assets—Derivatives	$	20.8	$	-2.5	$	-	$	-	$	-	$	18.3
	Deferred Charges and Other Assets—Derivatives		18.7		-		-		-		-		18.7
	Current Liabilities—Derivatives		15.4		-70.3		-		-1.7		8		-48.6
	Deferred Credits—Derivatives		17.7		-316.4		-		-		4		-294.7
	Total	$	72.6	$	-389.2	$	-	$	-1.7	$	12	$	-306.3
	As of September 30, 2013
	Current Assets—Derivatives	$	57.3	$	-19.3	$	-	$	-	$	-2.7	$	35.3
	Deferred Charges and Other Assets—Derivatives		57.4		-31.1		-		-		-		26.3
	Accounts Payable and Other Accrued Liabilities		1.5		-		-		-		-		1.5
	Current Liabilities—Derivatives		4.1		-53.4		-		-		0.9		-48.4
	Deferred Credits—Derivatives		-		-144		-		-		2.7		-141.3
	Total	$	120.3	$	-247.8	$	-	$	-	$	0.9	$	-126.6
Gains and (Losses) on Derivative Instruments	'
	WGL Holdings, Inc. Gains and Losses on Derivative Instruments
	(In millions)
	Fiscal Year Ended September 30,		2014		2013		2012
	Recorded to income
	Operating revenues—non-utility	$	-47.9	$	-9.9	$	19.2
	Utility cost of gas		-87.3		-45.9		22.3
	Non-utility cost of energy-related sales		36.2		-2.4		-34.2
	Other income-net		-1.1		0.2		0.9
	Interest expense		-0.2		-		-
	Recorded to regulatory assets
	Gas costs		-143.3		-115.1		42.2
	Other		0.2		-		-
	Recorded to other comprehensive income(a)		-1.5		-		-
	Total	$	-244.9	$	-173.1	$	50.4
	(a)This pre-tax unrealized gain represents the effective portion of our cash flow hedge. Upon settlement of the hedge, the realized gain or loss, to the extent effective, will be amortized as an adjustment to the interest expense. We expect this amortization to be minimal for fiscal 2015.
Washington Gas Light Company	'
Balance Sheet Classification of Derivative Instruments	'
	Washington Gas Light Company
	Balance Sheet Classification of Derivative Instruments(b)
	(In millions)
	As of September 30, 2014	Gross Derivative Assets		Gross Derivative Liabilities		Netting of Collateral		Total(a)
	Current Assets—Derivatives	$	3.9	$	-	$	-	$	3.9
	Deferred Charges and Other Assets—Derivatives		9.5		-		-		9.5
	Current Liabilities—Derivatives		8.6		-43.2		0.7		-33.9
	Deferred Credits—Derivatives		4.2		-265.2		0.2		-260.8
	Total	$	26.2	$	-308.4	$	0.9	$	-281.3
	As of September 30, 2013
	Current Assets—Derivatives	$	19.3	$	-12.3	$	-2.7	$	4.3
	Deferred Charges and Other Assets—Derivatives		47.2		-31.1		-		16.1
	Current Liabilities—Derivatives		1.5		-26.2		-		-24.7
	Deferred Credits—Derivatives		-		-106.1		-		-106.1
	Total	$	68	$	-175.7	$	-2.7	$	-110.4
	(a)WGL 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 815. All recognized derivative contracts and associated financial collateral subject to a master netting arrangement or similar that is eligible for offset under ASC 815 have been presented net in the balance sheet.
	(b)Washington Gas did not have any derivative instruments outstanding that were designated as hedging instruments at September 30, 2014, or 2013.
Gains and (Losses) on Derivative Instruments	'
	Washington Gas Gains and Losses on Derivative Instruments
	(In millions)
	Fiscal Year Ended September 30,		2014		2013		2012
	Recorded to income
	Utility cost of gas	$	-87.3	$	-45.9	$	22.3
	Recorded to regulatory assets
	Gas costs		-143.3		-115.1		42.2
	Other		0.2		-		-
	Total	$	-230.4	$	-161	$	64.5

Common_Stock_Tables

Common Stock (Tables)	12 Months Ended
	Sep. 30, 2014
Common Stock Tables [Abstract]	'
Common Stock Reserves	'
	Common Stock Reserves
	Reserve for:	Number of Shares
	Omnibus incentive compensation plan(a)	999,443
	Dividend reinvestment and common stock purchase plan	2,849,012
	Employee savings plans	637,196
	Directors’ stock compensation plan	96,650
	Total common stock reserves	4,582,301
	(a)In March 2007, WGL adopted a shareholder-approved Omnibus Incentive Compensation Plan to replace on a prospective basis the 1999 Incentive Compensation Plan. Included are shares that may be issued which would reduce the number of shares authorized under the Omnibus Incentive Compensation Plan. These shares include 301,378 shares dedicated to performance shares granted but not vested and include 5,318 shares dedicated to stock options issued but not exercised. Refer to Note 11 - Stock-Based Compensation for a discussion regarding our stock-based compensation plans.

Preferred_Stock_Tables

Preferred Stock (Tables)	12 Months Ended
	Sep. 30, 2014
Preferred Stock Tables [Abstract]	'
Preferred Stock Table	'
		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

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	12 Months Ended
	Sep. 30, 2014
Earnings Per Share Tables [Abstract]	'
Earnings per Share	'
	Basic and Diluted EPS
		Years Ended September 30,
	(In thousands, except per share data)		2014		2013		2012
	Basic earnings per average common share:
	Net income applicable to common stock	$	105,940	$	80,253	$	139,818
	Average common shares outstanding—basic		51,759		51,697		51,522
	Basic earnings per average common share	$	2.05	$	1.55	$	2.71
	Diluted earnings per average common share:
	Net income applicable to common stock	$	105,940	$	80,253	$	139,818
	Average common shares outstanding—basic		51,759		51,697		51,522
	Stock-based compensation plans		11		111		67
	Total average common shares outstanding—diluted		51,770		51,808		51,589
	Diluted earnings per average common share	$	2.05	$	1.55	$	2.71

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2014
Unrecognized Tax Benefits	'
	Unrecognized Tax Benefits
	(In thousands)		2014		2013		2012
	Total unrecognized tax benefits, October 1,	$	25,051	$	22,082	$	20,699
	Increases in tax positions relating to current year		10,512		5,251		3,396
	Decreases in tax positions relating to prior year		-2,950		-2,282		-2,013
	Total unrecognized tax benefits, September 30,	$	32,613	$	25,051	$	22,082
WGL Holdings, Inc.	'
Components of Income Tax Expense	'
	WGL Holdings, Inc.
	Components of Income Tax Expense
		Years Ended September 30,
	(In thousands)		2014		2013		2012
	INCOME TAX EXPENSE
	Current:
	Federal	$	29,976	$	41,425	$	-13,188
	State		5,149		11,258		-30
	Total current		35,125		52,683		-13,218
	Deferred:
	Federal
	Accelerated depreciation		35,747		33,394		45,506
	Other		-18,014		-31,173		44,727
	State
	Accelerated depreciation		9,822		6,795		9,412
	Other		-1,760		-7,585		8,054
	Total deferred		25,795		1,431		107,699
	Amortization of investment tax credits		-3,666		-1,822		-1,132
	Total income tax expense	$	57,254	$	52,292	$	93,349
Reconciliation Between the Statutory Federal Income Tax Rate and Effective Tax Rate	'
	WGL Holdings, Inc.
	Reconciliation Between the Statutory Federal Income Tax Rate and Effective Tax Rate
			Years Ended September 30,
	($ In thousands)		2014				2013				2012
	Income taxes at statutory federal income tax rate	$	57,580	35	%	$	46,853	35	%	$	82,070	35	%
	Increase (decrease) in income taxes resulting from:
	Accelerated depreciation less amount deferred		1,875	1.14			2,106	1.57			1,178	0.5
	Amortization of investment tax credits		-3,666	-2.23			-1,822	-1.36			-1,132	-0.48
	Cost of removal		-4,902	-2.98			-2,356	-1.76			-2,291	-0.98
	State income taxes-net of federal benefit		8,734	5.31			7,448	5.56			12,068	5.15
	Medicare Part D adjustment		-3,621	-2.2			-	-			2,827	1.21
	Other items-net		1,254	0.76			63	0.05			-1,371	-0.59
	Total income tax expense and effective tax rate	$	57,254	34.8	%	$	52,292	39.06	%	$	93,349	39.81	%
Components of Deferred Income Tax Assets (Liabilities)	'
	WGL Holdings, Inc.
	Components of Deferred Income Tax Assets (Liabilities)
			September 30,
	(In thousands)		2014				2013
	ACCUMULATED DEFERRED INCOME TAXES	Current		Non-current		Current		Non-current
	Deferred income tax assets:
	Pensions	$	-	$	24,349	$	-	$	17,362
	Other post-retirement benefits		-		-		-		18,510
	Uncollectible accounts		9,268		-		8,127		-
	Inventory overheads		6,591		-		6,431		-
	Capital gains/losses-net		-		-		2		-
	Valuation allowance		-		-		-2		-
	Employee compensation and benefits		6,306		37,873		5,876		37,301
	Customer advances		-		197		-		197
	Derivatives		6,503		31,555		-		7,872
	Deferred gas costs		-		4,218		4,911		-
	Solar grant/investment tax credit		-		39,184		-		17,415
	Other		814		1,225		816		2,530
	Total assets		29,482		138,601		26,161		101,187
	Deferred income tax liabilities:
	Other post-retirement benefits		-		38,299		-		-
	Accelerated depreciation and other plant related items		-		669,040		-		596,754
	Losses/gains on reacquired debt		-		1,426		-		1,567
	Income taxes recoverable through future rates		-		65,374		-		112,222
	Deferred gas costs		2,818		-		-		4,667
	Derivatives		-		-		1,639		-
	Partnership basis differences		-		25,370		-		15,784
	Total liabilities		2,818		799,509		1,639		730,994
	Net accumulated deferred income tax assets (liabilities)	$	26,664	$	-660,908	$	24,522	$	-629,807
Washington Gas Light Company	'
Components of Income Tax Expense	'
	Washington Gas Light Company
	Components of Income Tax Expense
				Years Ended September 30,
	(In thousands)			2014		2013		2012
	INCOME TAX EXPENSE
	Current:
	Federal		$	37,098	$	40,492	$	-13,155
	State			4,262		7,515		-3,332
	Total current			41,360		48,007		-16,487
	Deferred:
	Federal
	Accelerated depreciation			34,833		34,518		45,661
	Other			-30,523		-35,982		27,851
	State
	Accelerated depreciation			9,540		6,770		9,423
	Other			-6,800		-8,221		6,197
	Total deferred			7,050		-2,915		89,132
	Amortization of investment tax credits			-876		-895		-898
	Total income tax expense		$	47,534	$	44,197	$	71,747
Reconciliation Between the Statutory Federal Income Tax Rate and Effective Tax Rate	'
	Washington Gas Light Company
	Reconciliation Between the Statutory Federal Income Tax Rate and Effective Tax Rate
			Years Ended September 30,
	($ In thousands)		2014				2013				2012
	Income taxes at statutory federal income tax rate	$	51,050	35	%	$	40,782	35	%	$	63,628	35	%
	Increase (decrease) in income taxes resulting from:
	Accelerated depreciation less amount deferred		1,875	1.29			2,106	1.81			1,178	0.65
	Amortization of investment tax credits		-876	-0.6			-895	-0.77			-898	-0.49
	Cost of removal		-4,902	-3.36			-2,356	-2.02			-2,291	-1.26
	State income taxes-net of federal benefit		6,711	4.6			5,487	4.71			8,916	4.9
	Consolidated tax sharing allocation		-2,862	-1.96			-1,290	-1.11			-309	-0.17
	Medicare Part D adjustment		-3,621	-2.48			-	-			2,827	1.56
	Other items-net		159	0.09			363	0.31			-1,304	-0.72
	Total income tax expense and effective tax rate	$	47,534	32.58	%	$	44,197	37.93	%	$	71,747	39.47	%
Components of Deferred Income Tax Assets (Liabilities)	'
	Washington Gas Light Company
	Components of Deferred Income Tax Assets (Liabilities)
			Years Ended September 30,
	(In thousands)		2014				2013
	ACCUMULATED DEFERRED INCOME TAXES	Current		Non-current		Current		Non-current
	Deferred income tax assets:
	Pensions	$	-	$	23,738	$	-	$	16,768
	Other post-retirement benefits		-		-		-		18,474
	Uncollectible accounts		7,618		-		6,948		-
	Inventory overheads		6,591		-		6,431		-
	Employee compensation and benefits		5,902		27,961		5,756		27,125
	Customer advances		-		197		-		197
	Derivatives		4,809		31,555		2,138		7,872
	Deferred gas costs		-		4,218		4,911		-
	Investment tax credit		-		312		-		312
	Other		814		-		816		1,727
	Total assets		25,734		87,981		27,000		72,475
	Deferred income tax liabilities:
	Other post-retirement benefits		-		38,065		-		-
	Accelerated depreciation and other plant related items		-		602,376		-		565,996
	Losses/gains on reacquired debt		-		1,426		-		1,567
	Income taxes recoverable through future rates		-		65,128		-		111,698
	Deferred gas costs		2,818		-		-		4,667
	Other		-		932		-		-
	Total liabilities		2,818		707,927		-		683,928
	Net accumulated deferred income tax assets (liabilities)	$	22,916	$	-619,946	$	27,000	$	-611,453

Pension_and_Other_PostRetireme1

Pension and Other Post-Retirement Benefit Plans (Tables)	12 Months Ended
	Sep. 30, 2014
Pension And Other Post Retirement Benefit Plans Tables [Line Items]	'
Components of Net Periodic Benefit Costs (Income)	'
	Components of Net Periodic Benefit Costs (Income)
	(In millions)			Pension Benefits						Health and Life Benefits
	Year Ended September 30,			2014		2013		2012		2014		2013		2012
	Service cost		$	14	$	17	$	12.9	$	7.6	$	9.6	$	8
	Interest cost			40.4		36.6		40.5		18.7		18.8		25.1
	Expected return on plan assets			-41		-41.9		-43.5		-19.3		-18.3		-18.8
	Recognized prior service cost			0.3		1		1		-9.6		-3.9		-3.9
	Recognized actuarial loss			16.8		28.7		16.1		5		9.2		13.3
	Amortization of transition obligation			-		-		-		-		1.1		1.1
	Net periodic benefit cost			30.5		41.4		27		2.4		16.5		24.8
	Amount allocated to construction projects			-4.3		-5.7		-3.4		-0.4		-2.8		-3.7
	Amount deferred as regulatory asset (liability)-net			7		-3.7		-7.5		-2.3		2.4		1.5
	Amount charged (credited) to expense		$	33.2	$	32	$	16.1	$	-0.3	$	16.1	$	22.6
Unrecognized Costs Income Recorded On Balance Sheet [Table Text Block]	'
	Unrecognized Costs/Income Recorded on the Balance Sheet
	(In millions)				Pension Benefits				Health and Life Benefits
	September 30,			2014		2013		2014		2013
	Actuarial net loss			$	162.6	$	171.1	$	50.1	$	55.3
	Prior service cost (credit)				1.2		1.3		-149.3		-22.4
	Total			$	163.8	$	172.4	$	-99.2	$	32.9
	Regulatory asset (liability)			$	147.9	$	155.1	$	-94.6	$	31.3
	Pre-tax accumulated other comprehensive loss (gain)(a)				15.9		17.3		-4.6		1.6
	Total			$	163.8	$	172.4	$	-99.2	$	32.9
	(a)The total amount of accumulated other comprehensive loss recorded on our balance sheets at September 30, 2014 and 2013 is net of an income tax benefit of $4.9 million and $7.9 million, respectively.
Amount Recognized During Current Year [Table Text Block]	'
	Amounts Recognized During Fiscal Year 2014
		Regulatory assets/liabilities					Accumulated other comprehensive loss
	(In millions)	Pension Benefits		Health and Life Benefits			Pension Benefits		Health and Life Benefits
	Actuarial net loss	$	15.5	$	4.8		$	1.3	$	0.3
	Prior service cost (credit)		0.2		-9.1			0.1		-0.5
	Total	$	15.7	$	-4.3		$	1.4	$	-0.2
Post Retirement Benefits	'
	Post-Retirement Benefits
								Health and Life
	(In millions)			Pension Benefits(a)				Benefits
	Year Ended September 30,			2014		2013		2014		2013
	Change in projected benefit obligation(b)
	Benefit obligation at beginning of year		$	837.4	$	937.2	$	429.8	$	480.1
	Service cost			14		17		7.6		9.6
	Interest cost			40.4		36.6		18.7		18.8
	Change in plan benefits			-		-		-136.5		-
	Actuarial loss (gain)			68.6		-110		38.2		-62.3
	Retiree contributions			-		-		4.4		3.9
	Medicare Part D reimbursements			-		-		0.5		0.7
	Benefits paid			-43.3		-43.4		-19.5		-21
	Projected benefit obligation at end of year(b)		$	917.1	$	837.4	$	343.2	$	429.8
	Change in plan assets
	Fair value of plan assets at beginning of year		$	745.2	$	750.6	$	380.9	$	358.3
	Actual return on plan assets			103.3		38.6		57.8		19.9
	Company contributions			1.7		1.8		16		18
	Retiree contributions and Medicare Part D reimbursements			-		-		4.4		5.7
	Expenses			-2.2		-2.4		-		-
	Benefits paid			-43.3		-43.4		-19.5		-21
	Fair value of plan assets at end of year		$	804.7	$	745.2	$	439.6	$	380.9
	Funded status at end of year		$	-112.4	$	-92.2	$	96.4	$	-48.9
	Total amounts recognized on balance sheet
	Non-current asset		$	-	$	-	$	96.4	$	-
	Current liability			-4.2		-3.5		-		-
	Non-current liability			-108.2		-88.7		-		-48.9
	Total recognized		$	-112.4	$	-92.2	$	96.4	$	-48.9
	(a)The DB SERP and DB Restoration, included in pension benefits in the table above, have no assets.
	(b)For the Health and Life Benefits, the change in projected benefit obligation represents the accumulated benefit obligation.
Amount Recognized During Next Fiscal Year	'
	Amounts to be Recognized During Fiscal Year 2015
		Regulatory assets/liabilities					Accumulated other comprehensive loss
	(In millions)	Pension Benefits		Health and Life Benefits			Pension Benefits		Health and Life Benefits
	Actuarial net loss	$	17.1	$	4.2		$	1.7	$	0.2
	Prior service cost (credit)		0.2		-14.5			0.1		-0.7
	Total	$	17.3	$	-10.3		$	1.8	$	-0.5
Benefit Obligations Assumptions/Net Periodic Benefits Assumptions	'
	Benefit Obligations Assumptions
				Pension Benefits			Health and Life Benefits
	September 30,			2014	2013		2014	2013
	Discount rate(a)			4.00%-4.40%	4.50%-5.00%		4.40%	5.10%
	Rate of compensation increase			3.50%-4.10%	3.85%-5.15%		4.10%	3.85%
	(a)The decrease in the discount rate in fiscal year 2014 compared to prior years primarily reflects the decrease in long-term interest rates.
	Net Periodic Benefit Cost Assumptions
		Pension Benefits				Health and Life Benefits
	Years Ended September 30,	2014	2013	2012		2014	2013	2012
	Discount rate(a)	4.50%-5.00%	4.00%	5.30%		4.60%-5.10%	4.00%	5.10%
	Expected long-term return on plan assets(b)	6.50%	6.75%	7.50%		6.25%	6.75%	7.40%
	Rate of compensation increase(c)	3.85%-5.15%	3.85%-5.15%	3.85%-5.15%		3.85%	3.85%	3.85%-5.15%
	(a) The changes in the discount rates over the last two fiscal years primarily reflects 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 41.5%.
	(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.
Healthcare Trends	'
	Healthcare Trends
	(In millions)	One Percentage-Point Increase				One Percentage-Point Decrease
	Increase (decrease) total service and interest cost components	$	3.6			$	-2.7
	Increase (decrease) post-retirement benefit obligation	$	10.5			$	-9.2
Valuation Methods Level 3 assets	'
		(In millions)
		Years Ended September 30,			2014			2013
		Balance, beginning of year			$	21.1		$	18.7
		Actual return on plan assets:
			Assets still held at year end			2.7			2.4
		Balance, end of year			$	23.8		$	21.1
Expected Benefit Payments	'
		Expected Benefit Payments
		(In millions)	Pension Benefits			Health and Life Benefits
		2015	$	48.9		$	17.9
		2016		50.3			18.8
		2017		51.9			19.4
		2018		53			20.1
		2019		54.7			20.6
		2020—2024		286.5			105.3
Projected and accumulated benefit obligation	'
	Projected and accumulated benefit obligation
	(In millions)		Qualified Pension Plan				DB SERP				DB Restoration
	September 30,	2014		2013		2014		2013		2014		2013
	Projected benefit obligation	$	865.2	$	788.8	$	50.7	$	47.8	$	1.2	$	0.8
	Accumulated benefit obligation	$	801.9	$	737.2	$	46.2	$	43.9	$	0.7	$	0.5
Pension Plans Defined Benefit [Member]	'
Pension And Other Post Retirement Benefit Plans Tables [Line Items]	'
Pension and OPEB Plan Assets	'
		Pension Plan Assets
												% of
		($ In millions)		Level 1		Level 2		Level 3		Total		Total
		At September 30, 2014
		Cash and cash equivalents		$	0.6	$	-	$	-	$	0.6	0.1	%
		Equity securities
			U.S. Small Cap		32.3		-		-		32.3	4
			Preferred Securities		-		0.1		-		0.1	0
		Fixed income securities
			U.S. Treasuries		-		110.6		-		110.6	13.8
			U.S. Corporate Debt		-		108.4		-		108.4	13.5
			U.S. Agency Obligations and Government Sponsored Entities		-		24.6		-		24.6	3
			Asset-Backed Securities and Collateralized Mortgage Obligations		-		1.8		-		1.8	0.2
			Municipalities		-		9.2		-		9.2	1.1
			Non-U.S. Corporate Debt		-		23.8		-		23.8	3
			Repurchase Agreements(a)		-		2.5		-		2.5	0.3
			Other(b)		-		7		-		7	0.8
		Mutual Funds(c)			-		112.4		-		112.4	14
		Commingled Funds and Pooled Separate Accounts(d)			-		316.2		23.8		340	42.3
		Private Equity/Limited Partnerships(e)			-		30.5		-		30.5	3.8
		Derivatives(f)			-		-0.1		-		-0.1	0
		Total fair value of plan investments		$	32.9	$	747	$	23.8	$	803.7	99.9	%
		Receivable (payable)(g)									1	0.1
		Total plan assets at fair value								$	804.7	100	%
	Pension Plan Assets
											% of
	($ In millions)		Level 1		Level 2		Level 3		Total		Total
	At September 30, 2013
	Cash and cash equivalents		$	0.9	$	-	$	-	$	0.9	0.1	%
	Equity securities
		U.S. Small Cap		31.5		-		-		31.5	4.2
		Preferred Securities		-		0.1		-		0.1	-
	Fixed income securities
		U.S. Treasuries		-		124.5		-		124.5	16.7
		U.S. Corporate Debt		-		93.6		-		93.6	12.6
		U.S. Agency Obligations and Government Sponsored Entities		-		19		-		19	2.5
		Asset-Backed Securities and Collateralized Mortgage Obligations		-		1.9		-		1.9	0.2
		Municipalities		-		9		-		9	1.2
		Non-U.S. Corporate Debt		-		18.4		-		18.4	2.5
		Repurchase Agreements(a)		-		1		-		1	0.1
		Other(b)		-		5.7		-		5.7	0.8
	Mutual Funds(c)			-		93.2		-		93.2	12.5
	Commingled Funds and Pooled Separate Accounts(d)			-		295.5		21.1		316.6	42.5
	Private Equity/Limited Partnerships(e)			-		33.3		-		33.3	4.5
	Derivatives(f)			-		-0.3		-		-0.3	-
	Total fair value of plan investments		$	32.4	$	694.9	$	21.1	$	748.4	100.4	%
	Receivable (payable)(g)									-3.2	-0.4
	Total plan assets at fair value								$	745.2	100	%
	(a)	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.
	(b)	This category primarily includes Yankee bonds and non-U.S. government bonds.
	(c)	At September 30, 2014 and September 30, 2013, investments in mutual funds consisted primarily of corporate fixed income instruments.
	(d)	At September 30, 2014, investments in commingled funds and pooled separate accounts consisted primarily of 75% common stock of large-cap U.S. companies; 14% income producing properties located in the United States; 9% equity securities of non-U.S. companies; and 2% short-term money market investments. At September 30, 2013, investments in commingled funds and pooled separate accounts consisted primarily of 67% common stock of large-cap U.S. companies; 12% income producing properties located in the United States; 20% equity securities of non-U.S. companies; and 1% short-term money market investments.
	(e)	At September 30, 2014, investments in private equity/limited partnership consisted of common stock of international companies.
	(f)	At September 30, 2014, this category includes long-term U.S. Treasury interest rate futures contracts and interest rate put options.
Other PostretirementBenefit Plans Defined Benefit [Member]	'
Pension And Other Post Retirement Benefit Plans Tables [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, 2014
	Cash and Cash Equivalents		$	0.8	$	-	$	-	$	0.8	0.2	%
	Mutual Funds(a)			-		1.9		-		1.9	0.4
	Fixed Income Securities
		U.S Agency Obligations		-		2		-		2	0.5
		U.S. Treasuries		-		25.6		-		25.6	5.8
		U.S. Corporate Debt		-		34		-		34	7.7
		Municipalities		-		4.8		-		4.8	1.1
		Non-U.S. Corporate Debt		-		5.7		-		5.7	1.3
		Others(b)		-		5.3		-		5.3	1.2
	Commingled Funds(c)			-		359.7		-		359.7	81.8
	Total fair value of plan investments		$	0.8	$	439	$	-	$	439.8	100	%
	Receivable (payable)									-0.2	-
	Total plan assets at fair value								$	439.6	100	%
	At September 30, 2013
	Cash and Cash Equivalents		$	0.6	$	-	$	-	$	0.6	0.2	%
	Fixed Income Securities
		U.S Agency Obligations		-		1.7		-		1.7	0.4
		U.S. Treasuries		-		23.6		-		23.6	6.2
		U.S. Corporate Debt		-		28.7		-		28.7	7.5
		Municipalities		-		4.1		-		4.1	1.1
		Non-U.S. Corporate Debt		-		4.6		-		4.6	1.2
		Others(b)		-		5.3		-		5.3	1.4
	Commingled Funds(c)			-		311.2		-		311.2	81.7
	Total fair value of plan investments		$	0.6	$	379.2	$	-	$	379.8	99.7	%
	Receivable (payable)									1.1	0.3
	Total plan assets at fair value								$	380.9	100	%
	(a)	At September 30, 2014, investments in mutual funds consisted primarily of 63% short-term obligations consisting of certificates of deposit and time deposits, 23% high-quality commercial paper, 6% repurchase agreements, 4% corporate notes of U.S. and foreign corporations and 4% U.S. governmental and U.S. agency securities.
	(b)	At September 30, 2014 and 2013, this category consisted primarily of 82% non-U.S. government bonds and 18% Yankee bonds.
	(c)	At September 30, 2014 and 2013, investments in commingled funds consisted primarily of 66% common stock of large-cap U.S. companies, 17% U.S. agency obligations and government sponsored entities and 17% corporate bonds.

Stock_Based_Compensation_Table

Stock Based Compensation (Tables)	12 Months Ended
	Sep. 30, 2014
Performance Share Activity	'
	Performance Share Activity
		Year Ended
		30-Sep-14
		Number of Shares(a)		Weighted Average Grant-Date Fair Value
	Non-vested and outstanding, beginning of year	295,973		$	39.88
	Granted	109,076			42.88
	Vested	-84,849			41.14
	Cancelled/forfeited	-18,822			40.47
	Non-vested and outstanding, end of year	301,378		$	40.57
	(a)The number of common shares issued related to performance shares may range from zero to 200 percent of the number of shares shown in the table above based on our achievement of performance goals for total shareholder return relative to a selected peer group of companies.
Performance Share Fair Value Assumptions	'
	Fair Value Assumptions
	Years Ended September 30,	2014			2013			2012
	Expected stock-price volatility		19.1	%		19.4	%		27.8	%
	Dividend yield		3.93	%		3.98	%		3.97	%
	Weighted average grant-date fair value	$	42.88		$	39.73		$	38.99
Performance Unit Activity	'
	Performance Unit Activity
		Year Ended
		30-Sep-14
		Number of Units
	Non-vested and outstanding, beginning of year	11,582,556
	Granted	4,658,648
	Vested	-3,205,636
	Cancelled/forfeited	-766,647
	Non-vested and outstanding, end of year	12,268,921
Performance Units Fair Value Assumptions	'
	Fair Value Assumptions
		30-Sep-14
		10/1/2013 Grant	10/1/2012 Grant
	Expected stock-price volatility	18.10%	19.50%
Stock Option Activity	'
	Stock Option Activity
		Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (In years)	Aggregate Intrinsic Value (In thousands)
	Outstanding at September 30, 2013	26,372			$	31.34	4.01	$	235
	Granted	-				-	-		-
	Exercised	-21,054				31.34	-		232
	Cancelled/forfeited	-				-	-		-
	Outstanding at September 30, 2014	5,318			$	31.34	2	$	57
	Exercisable at September 30, 2014	5,318			$	31.34	2	$	57

Committments_and_Contingencies

Committments and Contingencies (Tables)	12 Months Ended
	Sep. 30, 2014
Commitments and Contingencies [Line Items]	'
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	'
	Minimum Payments Under Operating Leases
	(In millions)
	2015	$	7.8
	2016		6.3
	2017		4.9
	2018		4.3
	2019		1
	Thereafter		10.5
	Total	$	34.8
Washington Gas Light Company	'
Commitments and Contingencies [Line Items]	'
Long-term Purchase Commitment [Table Text Block]	'
		Washington Gas Contract Minimums
		(In millions)		Pipeline Contracts(a)			Gas Purchase Commitments(b)
		2015		$	195.4		$	280
		2016			224.7			288.9
		2017			217.7			336.7
		2018			211.1			323.2
		2019			201.3			303.5
		Thereafter			1,205.30			2,990.20
		Total		$	2,255.50		$	4,522.50
		(a) Represents minimum payments for natural gas transportation, storage and peaking contracts that have expiration dates through fiscal year 2032.
		(b) The contracts referenced above are estimated based on market prices at September 30, 2014.
Non Utility [Member]	'
Commitments and Contingencies [Line Items]	'
Long-term Purchase Commitment [Table Text Block]	'
		Contract Minimums
		WGEServices						WGL Midstream
	(In millions)	Gas Purchase Commitments(a)		Pipeline Contracts(b)		Electric Purchase Commitments(c)		Gas Purchase Commitments(d)		Pipeline Contracts(e)			Total
	2015	$	167.5	$	2.4	$	359.4	$	29.2	$	15.3	$	573.8
	2016		49.2		0.6		171.7		24.4		19.4		265.3
	2017		13.8		0.6		65		80.2		17.7		177.3
	2018		0.6		0.6		3.6		906		26.5		937.3
	2019		-		0.6		-		933.4		24.6		958.6
	Thereafter		-		1.3		-		13,479.80		260.9		13,742.00
	Total	$	231.1	$	6.1	$	599.7	$	15,453.00	$	364.4	$	16,654.30
	(a)Represents fixed price commitments with city gate equivalent deliveries.
	(b)Represents minimum payments for natural gas transportation, storage and peaking contracts that have expiration dates through fiscal year 2025.
	(c)Represents electric purchase commitments that are based on existing fixed price and fixed volume contracts. Includes $15.3 million of commitments related to renewable energy credits.
	(d)Includes short-term commitments to purchase fixed volumes of natural gas, as well as long-term gas purchase commitments that contain fixed volume purchase requirements. Cost estimates are based on forward market prices for purchases under these purchase commitments.
	(e)Represents minimum payments for natural gas transportation, storage and peaking contracts that have expiration dates through fiscal year 2044.

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Sep. 30, 2014
Quantitative Information about Level 3 Fair Value Measurements	'
	Quantitative Information about Level 3 Fair Value Measurements
	(In millions)	Net Fair Value September 30, 2014	Valuation Techniques	Unobservable Inputs	Range
	WGL Holdings, Inc.	(In millions)
	Natural gas related derivatives	($294.70)	Discounted Cash Flow	Natural Gas Basis Price (per dekatherm)	($2.101) -	$6.15
			Option Model	Natural Gas Basis Price (per dekatherm)	($1.675) -	$6.15
				Annualized Volatility of Spot Market Natural Gas	30.9% -	589.60%
	Electricity related derivatives	($5.00)	Discounted Cash Flow	Electricity Congestion Price (per megawatt hour)	($2.85) -	$90.95
			Internal Model	Electricity Congestion Price (per megawatt hour)
			Option Model	Electricity Congestion Price (per megawatt hour)
				Annualized Volatility of Electricity Prices
	Washington Gas Light Company
	Natural gas related derivatives	($270.60)	Discounted Cash Flow	Natural Gas Basis Price (per dekatherm)	($2.101) -	$6.15
	Quantitative Information about Level 3 Fair Value Measurements
	(In millions)	Net Fair Value September 30, 2013	Valuation Techniques	Unobservable Inputs	Range
	WGL Holdings, Inc.	(In millions)
	Natural gas related derivatives	($155.20)	Discounted Cash Flow	Natural Gas Basis Price (per dekatherm)	($1.780) -	$2.21
			Option Model	Natural Gas Basis Price (per dekatherm)	($0.181) -	$0.63
				Annualized Volatility of Spot Market Natural Gas	34.6% -	276.60%
	Electricity related derivatives	$2.40	Discounted Cash Flow	Electricity Congestion Price (per megawatt hour)	($1.995) -	$64.15
	Washington Gas Light Company
	Natural gas related derivatives	($133.60)	Discounted Cash Flow	Natural Gas Basis Price (per dekatherm)	($1.780) -	$2.21
			Option Model	Natural Gas Basis Price (per dekatherm)	$0.024 -	$0.63
				Annualized Volatility of Spot Market Natural Gas	46.8% -	276.60%
WGL Holdings, Inc.	'
Fair Value Measurements Under the Fair Value Hierarchy	'
	WGL Holdings, Inc.
	Fair Value Measurements Under the Fair Value Hierarchy
	(In millions)	Level 1		Level 2		Level 3		Total
	At September 30, 2014
	Assets
	Natural gas related derivatives	$	-	$	22.7	$	33.7	$	56.4
	Electricity related derivatives		-		0.3		15.9		16.2
	Total Assets	$	-	$	23	$	49.6	$	72.6
	Liabilities
	Natural gas related derivatives	$	-	$	-39.8	$	-328.4	$	-368.2
	Electricity related derivatives		-		-0.1		-20.9		-21
	Interest rate derivatives		-		-1.7		-		-1.7
	Total Liabilities	$	-	$	-41.6	$	-349.3	$	-390.9
	At September 30, 2013
	Assets
	Natural gas related derivatives	$	-	$	72.3	$	21.5	$	93.8
	Electricity related derivatives		-		-		25.4		25.4
	Warrants		-		-		1.1		1.1
	Total Assets	$	-	$	72.3	$	48	$	120.3
	Liabilities
	Natural gas related derivatives	$	-	$	-41.1	$	-176.7	$	-217.8
	Electricity related derivatives		-		-7		-23		-30
	Total Liabilities	$	-	$	-48.1	$	-199.7	$	-247.8
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'
	WGL Holdings, Inc. Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs
	(In millions)		Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Fiscal Year Ended September 30, 2014
	Balance at October 1, 2013	$	-155.2	$	2.4	$	-	$	1.1	$	-151.7
	Realized and unrealized gains (losses)
	Recorded to income		-72.6		-5.7		-		-1.1		-79.4
	Recorded to regulatory assets - gas costs		-113.6		-		-		-		-113.6
	Transfers out of Level 3		1.7		-		-		-		1.7
	Purchases		-		5.2		-		-		5.2
	Settlements		45		-6.9		-		-		38.1
	Balance at September 30, 2014	$	-294.7	$	-5	$	-	$	-	$	-299.7
	WGL Holdings, Inc. Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs
	(In millions)		Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Fiscal Year Ended September 30, 2013
	Balance at October 1, 2012	$	39.6	$	2.8	$	-0.5	$	0.9	$	42.8
	Realized and unrealized gains (losses)
	Recorded to income		-72.4		-23.8		1.2		0.2		-94.8
	Recorded to regulatory assets - gas costs		-115.3		-		-		-		-115.3
	Transfers out of Level 3		-17.4		-		-0.7		-		-18.1
	Purchases		-		5.7		-		-		5.7
	Settlements		10.3		17.7		-		-		28
	Balance at September 30, 2013	$	-155.2	$	2.4	$	-	$	1.1	$	-151.7
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'
	WGL Holdings, Inc. Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements
	Fiscal Year Ended September 30, 2014
	(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Operating revenues—non-utility	$	-2.3	$	-22.1	$	-	$	-	$	-24.4
	Utility cost of gas		-69.4		-		-		-		-69.4
	Other income-net		-		-		-		-1.1		-1.1
	Non-utility cost of energy-related sales		-0.9		16.4		-		-		15.5
	Total	$	-72.6	$	-5.7	$	-	$	-1.1	$	-79.4
	WGL Holdings, Inc. Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements
	Fiscal Year Ended September 30, 2013
	(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Operating revenues—non-utility	$	-27	$	-9.1	$	-	$	-	$	-36.1
	Utility cost of gas		-45.8		-		-		-		-45.8
	Other income-net		-		-		-		0.2		0.2
	Non-utility cost of energy-related sales		0.4		-14.7		-		-		-14.3
	Operation and maintenance expense		-		-		1.2		-		1.2
	Total	$	-72.4	$	-23.8	$	1.2	$	0.2	$	-94.8
	WGL Holdings, Inc. Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements
	Fiscal Year Ended September 30, 2012
	(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Operating revenues—non-utility	$	3	$	-14.2	$	-	$	-	$	-11.2
	Utility cost of gas		14.3		-		-		-		14.3
	Other income-net		-		-		-		0.9		0.9
	Non-utility cost of energy-related sales		4.8		-33.5		-		-		-28.7
	Operation and maintenance expense		-		-		7.9		-		7.9
	Total	$	22.1	$	-47.7	$	7.9	$	0.9	$	-16.8
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'
	WGL Holdings, Inc. Unrealized Gains (Losses) Recorded for Level 3 Measurements
	Fiscal Year Ended September 30, 2014
	(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Recorded to income
	Operating revenues—non-utility	$	-5	$	-33.8	$	-	$	-	$	-38.8
	Utility cost of gas		-60.6		-		-		-		-60.6
	Non-utility cost of energy-related sales		3.7		30		-		-		33.7
	Other income-net		-		-		-		-1.1		-1.1
	Recorded to regulatory assets—gas costs		-109.9		-		-		-		-109.9
	Total	$	-171.8	$	-3.8	$	-	$	-1.1	$	-176.7
	WGL Holdings, Inc. Unrealized Gains (Losses) Recorded for Level 3 Measurements
	Fiscal Year Ended September 30, 2013
	(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Recorded to income
	Operating revenues—non-utility	$	-25.3	$	6.6	$	-	$	-	$	-18.7
	Utility cost of gas		-44.3		-		-		-		-44.3
	Non-utility cost of energy-related sales		0.2		-1.1		-		-		-0.9
	Other income-net		-		-		-		0.2		0.2
	Recorded to regulatory assets—gas costs		-111.6		-		-		-		-111.6
	Total	$	-181	$	5.5	$	-	$	0.2	$	-175.3
	WGL Holdings, Inc. Unrealized Gains (Losses) Recorded for Level 3 Measurements
	Fiscal Year Ended September 30, 2012
	(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Derivatives		Warrants		Total
	Recorded to income
	Operating revenues—non-utility	$	4.3	$	4.8	$	-	$	-	$	9.1
	Utility cost of gas		13.8		-		-		-		13.8
	Non-utility cost of energy-related sales		0.8		14		-		-		14.8
	Other income-net		-		-		-		0.9		0.9
	Operation and maintenance expense		-		-		0.2		-		0.2
	Recorded to regulatory assets—gas costs		23.2		-		-		-		23.2
	Total	$	42.1	$	18.8	$	0.2	$	0.9	$	62
Fair Value of Financial Instruments	'
	WGL Holdings, Inc. Fair Value of Financial Instruments
	At September 30,	2014				2013
	(In millions)		Carrying Amount		Fair Value		Carrying Amount		Fair Value
	Money market funds (a)	$	9.7	$	9.7	$	6.5	$	6.5
	Other short- term investments(a)	$	-	$	-	$	0.1	$	0.1
	Commercial paper (b)	$	453.5	$	453.5	$	373.1	$	373.1
	Long-term debt(c)	$	679.2	$	809.3	$	524.1	$	630.2
Washington Gas Light Company	'
Fair Value Measurements Under the Fair Value Hierarchy	'
	Washington Gas Light Company
	Fair Value Measurements Under the Fair Value Hierarchy
	(In millions)	Level 1		Level 2		Level 3		Total
	At September 30, 2014
	Assets
	Natural gas related derivatives	$	-	$	13.5	$	12.7	$	26.2
	Total Assets	$	-	$	13.5	$	12.7	$	26.2
	Liabilities
	Natural gas related derivatives	$	-	$	-25.1	$	-283.3	$	-308.4
	Total Liabilities	$	-	$	-25.1	$	-283.3	$	-308.4
	At September 30, 2013
	Assets
	Natural gas related derivatives	$	-	$	51	$	17	$	68
	Total Assets	$	-	$	51	$	17	$	68
	Liabilities
	Natural gas related derivatives	$	-	$	-25.1	$	-150.6	$	-175.7
	Total Liabilities	$	-	$	-25.1	$	-150.6	$	-175.7
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'
	Washington Gas Light Company Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs
	(In millions)		Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Fiscal Year Ended September 30, 2014
	Balance at October 1, 2013	$	-133.6	$	-	$	-	$	-	$	-133.6
	Realized and unrealized gains (losses)
	Recorded to income		-69.4		-		-		-		-69.4
	Recorded to regulatory assets - gas costs		-113.6		-		-		-		-113.6
	Transfers out of Level 3		1.7		-		-		-		1.7
	Settlements		44.3		-		-		-		44.3
	Balance at September 30, 2014	$	-270.6	$	-	$	-	$	-	$	-270.6
	Washington Gas Light Company Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs
	(In millions)		Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Fiscal Year Ended September 30, 2013
	Balance at October 1, 2012	$	35.6	$	-	$	-0.5	$	-	$	35.1
	Realized and unrealized gains (losses)
	Recorded to income		-45.9		-		1.2		-		-44.7
	Recorded to regulatory assets - gas costs		-115.3		-		-		-		-115.3
	Transfers out of Level 3		-17.4		-		-0.7		-		-18.1
	Settlements		9.4		-		-		-		9.4
	Balance at September 30, 2013	$	-133.6	$	-	$	-	$	-	$	-133.6
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'
	Washington Gas Light Company Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements
	Fiscal Year Ended September 30, 2014
	(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Utility cost of gas	$	-69.4	$	-	$	-	$	-	$	-69.4
	Total	$	-69.4	$	-	$	-	$	-	$	-69.4
	Washington Gas Light Company Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements
	Fiscal Year Ended September 30, 2013
	(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Utility cost of gas	$	-45.9	$	-	$	-	$	-	$	-45.9
	Operation and maintenance expense		-		-		1.2		-		1.2
	Total	$	-45.9	$	-	$	1.2	$	-	$	-44.7
	Washington Gas Light Company Realized and Unrealized Gains (Losses) Recorded for Level 3 Measurements
	Fiscal Year Ended September 30, 2012
	(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Utility cost of gas	$	14.3	$	-	$	-	$	-	$	14.3
	Operation and maintenance expense		-		-		7.9		-		7.9
	Total	$	14.3	$	-	$	7.9	$	-	$	22.2
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'
	Washington Gas Light Company Unrealized Gains (Losses) Recorded for Level 3 Measurements
	Fiscal Year Ended September 30, 2014
	(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Recorded to income
	Utility cost of gas	$	-60.6	$	-	$	-	$	-	$	-60.6
	Recorded to regulatory assets—gas costs		-109.9		-		-		-		-109.9
	Total	$	-170.5	$	-	$	-	$	-	$	-170.5
	Washington Gas Light Company Unrealized Gains (Losses) Recorded for Level 3 Measurements
	Fiscal Year Ended September 30, 2013
	(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Recorded to income
	Utility cost of gas	$	-44.3	$	-	$	-	$	-	$	-44.3
	Recorded to regulatory assets—gas costs		-111.6		-		-		-		-111.6
	Total	$	-155.9	$	-	$	-	$	-	$	-155.9
	Washington Gas Light Company Unrealized Gains (Losses) Recorded for Level 3 Measurements
	Fiscal Years Ended September 30, 2012
	(In millions)	Natural Gas Related Derivatives		Electricity Related Derivatives		Weather Related Instruments		Warrants		Total
	Recorded to income
	Utility cost of gas	$	13.8	$	-	$	-	$	-	$	13.8
	Operation and maintenance expense		-		-		0.2		-		0.2
	Recorded to regulatory assets—gas costs		23.2		-		-		-		23.2
	Total	$	37	$	-	$	0.2	$	-	$	37.2
Fair Value of Financial Instruments	'
	Washington Gas Light Company Fair Value of Financial Instruments
	At September 30,	2014				2013
	(In millions)		Carrying Amount		Fair Value		Carrying Amount		Fair Value
	Money market funds (a)	$	4.3	$	4.3	$	3.1	$	3.1
	Other short- term investments(a)	$	-	$	-	$	0.1	$	0.1
	Commercial paper (b)	$	89	$	89	$	124.5	$	124.5
	Long-term debt(c)	$	679.2	$	809.3	$	524.1	$	630.2
	(a)Balance located in cash and cash equivalents in the accompanying balance sheets. These amounts may be offset by outstanding checks.
	(b)Balance is located in notes payable in the accompanying balance sheets.
	(c)Less current maturities and unamortized discounts.

Operating_Segment_Reporting_Ta

Operating Segment Reporting (Tables)	12 Months Ended
	Sep. 30, 2014
Segment Reporting Information Operating Income Loss Table [Abstract]	'
Operating Segment Financial Information	'
	Operating Segment Financial Information
							Non-Utility Operations
	(In thousands)				Regulated Utility		Retail Energy-Marketing	Commercial Energy Systems		Midstream Energy Services		Other Activities		Eliminations(b)		Consolidated
	Year Ended September 30, 2014
	Operating Revenues (a)			$	1,443,800	$	1,310,279	$	40,679	$	16,555	$	-	$	-30,366	$	2,780,947
	Operating Expenses:
		Cost of Energy-Related Sales			726,879		1,238,970		20,348		-		-		-30,613		1,955,584
		Operation			234,391		43,750		10,419		8,517		11,749		75		308,901
		Maintenance			56,972		-		-		-		-		-		56,972
		Depreciation and Amortization			104,064		756		6,178		124		-		-350		110,772
		General Taxes and Other Assessments:
			Revenue Taxes		84,287		8,276		5		-		-		-		92,568
			Other		53,402		4,615		253		274		84		-		58,628
			Total Operating Expenses	$	1,259,995	$	1,296,367	$	37,203	$	8,915	$	11,833	$	-30,888	$	2,583,425
	Operating Income (Loss)				183,805		13,912		3,476		7,640		-11,833		522		197,522
	Equity in Earnings of Unconsolidated Affiliates				-		1		1,953		771		469		-		3,194
	Other Income (Expense)—Net				863		103		1,007		-239		-198		-		1,536
	Interest Expense				37,127		10		-		-		601		-		37,738
	Dividends on Washington Gas Preferred Stock				1,320		-		-		-		-		-		1,320
	Income Tax Expense				48,181		5,764		1,019		1,969		111		210		57,254
	Net Income (Loss) Applicable to Common Stock			$	98,040	$	8,242	$	5,417	$	6,203	$	-12,274	$	312	$	105,940
	Total Assets at September 30, 2014			$	3,979,522	$	389,700	$	521,570	$	211,824	$	369,816	$	-615,933	$	4,856,499
	Capital Expenditures			$	286,323	$	76	$	108,363	$	-	$	-	$	-	$	394,762
	Equity Method Investments at September 30, 2014			$	-	$	-	$	66,810	$	28,076	$	16	$	-	$	94,902
	(a)Operating revenues are reported gross of revenue taxes. Revenue taxes of both the regulated utility and the retail energy-marketing segments include gross receipt taxes. Revenue taxes of the regulated utility segment also include PSC fees, franchise fees and energy taxes. Operating revenue amounts in the "Eliminations" column represent total intersegment revenues associated with sales from the regulated utility segment to the retail energy-marketing segment. Midstream Energy Services' cost of energy related sales is netted with its gross revenues.
	(b)Intersegment eliminations net income includes a timing difference between Commercial Energy Systems' recognition of revenue for the sale of Solar Renewable Energy Credits (SRECs) to Retail Energy-Marketing and Retail Energy's Marketing's recognition of the associate expense. Retail Energy-Marketing has recorded a portion of the SREC's purchased as inventory to be used in future periods at which time they will be expensed.
	Operating Segment Financial Information
							Non-Utility Operations
	(In thousands)				Regulated Utility		Retail Energy-Marketing	Commercial Energy Systems		Midstream Energy Services		Other Activities		Eliminations(b)			Consolidated
	Year Ended September 30, 2013
	Operating Revenues(a)			$	1,200,357	$	1,279,364	$	35,217	$	-20,390	$	-	$	-28,410	$	2,466,138
	Operating Expenses:
		Cost of Energy-Related Sales			521,508		1,164,831		24,450		-		-		-26,458		1,684,331
		Operation			243,341		49,574		6,875		8,683		9,344		-197		317,620
		Maintenance			49,269		-		-		-		-		-		49,269
		Depreciation and Amortization			100,438		726		2,411		124		-		-415		103,284
		General Taxes and Other Assessments:
			Revenue Taxes		81,422		6,831		7		-		-		-		88,260
			Other		52,271		4,411		303		474		97		-		57,556
			Total Operating Expenses	$	1,048,249	$	1,226,373	$	34,046	$	9,281	$	9,441	$	-27,070	$	2,300,320
	Operating Income (Loss)				152,108		52,991		1,171		-29,671		-9,441		-1,340		165,818
	Equity in Earnings of Unconsolidated Affiliates				-		-		1,070		312		128		-		1,510
	Other Income (Expense)—Net				1,539		273		778		-		644		-686		2,548
	Interest Expense				35,631		13		234		417		402		-686		36,011
	Dividends on Washington Gas Preferred Stock				1,320		-		-		-		-		-		1,320
	Income Tax Expense (Benefit)				44,883		20,227		-206		-10,951		-1,124		-537		52,292
	Net Income (Loss) Applicable to Common Stock			$	71,813	$	33,024	$	2,991	$	-18,825	$	-7,947	$	-803	$	80,253
	Total Assets at September 30, 2013			$	3,486,296	$	403,082	$	318,995	$	231,368	$	290,440	$	-470,121	$	4,260,060
	Capital Expenditures			$	227,948	$	730	$	83,667	$	-	$	-	$	-	$	312,345
	Equity Method Investments at September 30, 2013			$	-	$	-	$	54,977	$	6,507	$	413	$	-	$	61,897
	(a)Operating revenues are reported gross of revenue taxes. Revenue taxes of both the regulated utility and the retail energy-marketing segments include gross receipt taxes. Revenue taxes of the regulated utility segment also include PSC fees, franchise fees and energy taxes. Operating revenue amounts in the "Eliminations" column represent total intersegment revenues associated with sales from the regulated utility segment to the retail energy-marketing segment. Midstream Energy Services' cost of energy related sales is netted with its gross revenues.
	(b)Intersegment eliminations net income includes a timing difference between Commercial Energy Systems' recognition of revenue for the sale of Solar Renewable Energy Credits (SRECs) to Retail Energy- Marketing and Retail Energy's Marketing's recognition of the associate expense. Retail Energy- Marketing has recorded a portion of the SREC's purchased as inventory to be used in future periods at which time will be expensed.
	Operating Segment Financial Information
							Non-Utility Operations
	(In thousands)				Regulated Utility		Retail Energy-Marketing	Commercial Energy Systems		Midstream Energy Services		Other Activities		Eliminations(b)			Consolidated
	Year Ended September 30, 2012
	Operating Revenues			$	1,137,666	$	1,267,070	$	60,325	$	-11,221	$	-	$	-28,530	$	2,425,310
	Operating Expenses:
		Cost of Energy-Related Sales			421,539		1,139,162		51,149		-		-		-26,802		1,585,048
		Operation			227,362		52,161		5,414		2,860		3,612		-1,093		290,316
		Maintenance			52,494		-		-		-		-		-		52,494
		Depreciation and Amortization			94,998		735		1,261		116		-		-634		96,476
		General Taxes and Other Assessments:
		Revenue Taxes		74,244		5,776		8		-		-		-		80,028
		Other		50,822		4,070		280		240		16		-1		55,427
		Total Operating Expenses	$	921,459	$	1,201,904	$	58,112	$	3,216	$	3,628	$	-28,530	$	2,159,789
Operating Income (Loss)				216,207		65,166		2,213		-14,437		-3,628		-		265,521
Equity in Earnings of Unconsolidated Affiliates				-		-		947		-		293		-		1,240
Other Income—Net				3,085		42		-32		-		1,097		-38		4,154
Interest Expense				36,098		1		1		-		366		-38		36,428
Dividends on Washington Gas Preferred Stock				1,320		-		-		-		-		-		1,320
Income Tax Expense (Benefit)				72,178		25,876		760		-5,347		-118		-		93,349
Net Income (Loss) Applicable to Common Stock			$	109,696	$	39,331	$	2,367	$	-9,090	$	-2,486	$	-	$	139,818
Total Assets at September 30, 2012			$	3,516,046	$	361,801	$	148,407	$	169,456	$	211,038	$	-295,801	$	4,110,947
Capital Expenditures			$	208,225	$	984	$	41,818	$	101	$	-	$	-	$	251,128
Equity Method Investments at September 30, 2012			$	-	$	-	$	23,346	$	-	$	-	$	-	$	23,346
(a)Operating revenues are reported gross of revenue taxes. Revenue taxes of both the regulated utility and the retail energy-marketing segments include gross receipt taxes. Revenue taxes of the regulated utility segment also include PSC fees, franchise fees and energy taxes. Operating revenue amounts in the "Eliminations" column represent total intersegment revenues associated with sales from the regulated utility segment to the retail energy-marketing segment. Midstream Energy Services' cost of energy related sales is netted with its gross revenues.
(b)Intersegment eliminations net income includes a timing difference between Commercial Energy Systems' recognition of revenue for the sale of Solar Renewable Energy Credits (SRECs) to Retail Energy-Marketing and Retail Energy's Marketing's recognition of the associate expense. Retail Energy-Marketing has recorded a portion of the SREC's purchased as inventory to be used in future periods at which time they will be expensed.

Related_Party_Transactions_Tab

Related Party Transactions (Tables)	12 Months Ended
	Sep. 30, 2014
Related Party Transactions [Abstract]	'
Receivables and Payables from Associated Companies	'
	Washington Gas Light Company
	Receivables / Payables from Associated Companies
	(In millions)	30-Sep-14			30-Sep-13
	Receivables from Associated Companies	$	4.8		$	7.2
	Payables to Associated Companies	$	54.7		$	20.6
	Washington Gas - Gas Balancing Service Charges
			Years Ended September 30,
	(In millions)		2014		2013		2012
	Gas balancing service charge	$	26.6	$	25	$	26.8

Other_Investment_Tables

Other Investment (Tables)	12 Months Ended
	Sep. 30, 2014
Other Investments [Abstract]	'
Minimum Payments Receivable for Direct Financing Leases	'
		Minimum Payments Receivable for Direct Financing Leases
		(In millions)
		2015	$	2.3
		2016		2
		2017		1.9
		2018		1.8
		2019		1.7
		Thereafter		12.3
		Total	$	22
Location of Investments	'
	WGL Holdings, Inc Balance Sheet Location of Other Investments
	As of September 30, 2014 (in millions)		VIEs		Non-VIEs		Total
	Assets
	Investments in unconsolidated affiliates	$	72.6	$	27.9	$	100.5
	Investments in direct financing leases, capital leases		18.2		-		18.2
	Accounts receivable		1.7		-		1.7
	Total assets	$	92.5	$	27.9	$	120.4
	WGL Holdings, Inc. Balance Sheet Location of Other Investments
	As of September 30, 2013 (in millions)		VIEs		Non-VIEs		Total
	Assets
	Investments in unconsolidated affiliates	$	55.4	$	12.1	$	67.5
	Investments in direct financing leases, capital leases		23.4		-		23.4
	Deferred charges and other assets- derivatives		-		1.1		1.1
	Accounts receivable		5.8		-		5.8
	Total assets	$	84.6	$	13.2	$	97.8
	Liabilities
	Other	$	8.5	$	-	$	8.5
	Total liabilities	$	8.5	$	-	$	8.5
	WGL Holdings, Inc.
	Income Statement Location of Other Investments
		Fiscal year ended
		30-Sep-14
	(in millions)	VIEs			Non-VIEs	Total
	Equity in earnings of unconsolidated affiliates	$	2.2	$	1	$	3.2
	Depreciation and amortization	$	0.2	$	-	$	0.2
	Other income - net	$	2.6		-		2.6
	Net Income	$	4.6	$	1	$	5.6
	WGL Holdings, Inc.
	Income Statement Location of Other Investments
		Fiscal year ended
		30-Sep-13
	(in millions)	VIEs			Non-VIEs	Total
	Equity in earnings of unconsolidated affiliates	$	1	$	0.5	$	1.5
	Depreciation and amortization		0.1		-		0.1
	Other income- net		1.4		-		1.4
	Net Income	$	2.3	$	0.5	$	2.8

Changes_in_Accumulated_Other_C1

Changes in Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Sep. 30, 2014
WGL Holdings, Inc.	'
Schedule Of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	'
	WGL Holdings, Inc.
	Changes in Accumulated Other Comprehensive Income by Component
			September 30,
	(In thousands)		2014		2013
	Beginning Balance	$	-11,048	$	-12,201
	Qualified cash flow hedging instruments(c )		-1,548		-
	Change in prior service cost (credit) (a) (b)		6,095		-1,671
	Amortization of actuarial gain (a)		1,594		3,399
	Amortization of transition obligation (a)		-		238
	Current-period other comprehensive income		6,141		1,966
	Income tax expense related to other comprehensive income (b)		3,054		813
	Ending Balance	$	-7,961	$	-11,048
	(a) These accumulated other comprehensive income components are included in the computation of net periodic benefit cost. Refer to Note 10-Pension and other post-retirement benefit plans for additional details.
	(b) The majority of the 2014 change to the prior service cost component of other comprehensive income is related to the impact of the OPEB plan amendment and re-measurement. Refer to Note 10-Pension and other post-retirement benefit plans for additional details.
	(c ) Cash flow hedging instruments represent interest rate swap agreements on debt issuances. Refer to Note 14 - Derivative and Weather-related Instruments for further discussion of the interest rate swap agreements.
Washington Gas Light Company	'
Schedule Of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	'
	Washington Gas Light Company
	Changes in Accumulated Other Comprehensive Income by Component
			September 30,
	(In thousands)		2014		2013
	Beginning Balance	$	-11,048	$	-12,201
	Change in prior service cost (credit) (a) (b)		6,095		-1,671
	Amortization of actuarial gain (a)		1,594		3,399
	Amortization of transition obligation (a)		-		238
	Current-period other comprehensive income		7,689		1,966
	Income tax expense related to other comprehensive income (b)		3,054		813
	Ending Balance	$	-6,413	$	-11,048
	(a) These accumulated other comprehensive income components are included in the computation of net periodic benefit cost. Refer to Note 10-Pension and other post-retirement benefit plans for additional details.
	(b) The majority of the 2014 change to the prior service cost component of other comprehensive income is related to the impact of the OPEB plan amendment and re-measurement. Refer to Note 10-Pension and other post-retirement benefit plans for additional details.

Quarterly_Financial_Informatio1

Quarterly Financial Information (Tables)	12 Months Ended
	Sep. 30, 2014
Quarterly Financial Information Disclosure [Abstract]	'
Schedule Of Quarterly Financial Information [Table Text Block]	'
	##XSQuarter Ended
	(In thousands, except per share data)	December 31			March 31		June 30	30-Sep
	Fiscal Year 2014
	WGL Holdings, Inc.
	Operating revenues	$	680,297	$	1,174,250	$	467,500	$	458,900
	Operating income (loss)	$	32,712	$	104,733	$	-9,489	$	69,566
	Net income (loss) applicable to common stock	$	18,629	$	61,213	$	-11,940	$	38,038
	Earnings (loss) per average share of common stock:
	Basic	$	0.36	$	1.18	$	-0.23	$	0.74
	Diluted	$	0.36	$	1.18	$	-0.23	$	0.74
	Washington Gas Light Company
	Operating revenues	$	390,415	$	716,808	$	197,752	$	138,825
	Operating income	$	65,229	$	88,038	$	4,326	$	24,530
	Net income (loss) applicable to common stock	$	38,477	$	49,176	$	-521	$	9,872
	Fiscal Year 2013
	WGL Holdings, Inc.
	Operating revenues	$	686,736	$	891,383	$	478,118	$	409,901
	Operating income (loss)	$	94,616	$	155,584	$	-9,111	$	-75,270
	Net income (loss) applicable to common stock	$	52,388	$	89,505	$	-10,015	$	-51,625
	Earnings (loss) per average share of common stock:
	Basic	$	1.01	$	1.73	$	-0.19	$	-1
	Diluted	$	1.01	$	1.73	$	-0.19	$	-1
	Washington Gas Light Company
	Operating revenues	$	355,817	$	535,950	$	180,882	$	127,708
	Operating income (loss)	$	72,037	$	134,358	$	-368	$	-55,421
	Net income (loss) applicable to common stock	$	38,387	$	76,935	$	-4,531	$	-39,789

Accounting_Policies_Narrative_

Accounting Policies (Narrative) (Details) (USD $)

12 Months Ended

3 Months Ended

12 Months Ended

3 Months Ended

12 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2014

Jun. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

WGL Holdings, Inc.

WGL Holdings, Inc.

WGL Holdings, Inc.

Washington Gas Light Company

Washington Gas Light Company

Washington Gas Light Company

WGEServices

WGEServices

WGEServices

WGL Midstream

WGL Midstream

WGL Midstream

Natural Gas Customers

Abandoned LNG storage project

Abandoned LNG storage project

Abandoned LNG storage project

Abandoned LNG storage project

Springfield Operations Center

Springfield Operations Center

Springfield Operations Center

Springfield Operations Center

Springfield Operations Center

Interruptible Customers [Member]

Firm Customer [Member]

Electric Generation Customers [Member]

Electricity Customers [Member]

WGEServices

Washington Gas Light Company

Washington Gas Light Company

Washington Gas Light Company

Washington Gas Light Company

Washington Gas Light Company

Washington Gas Light Company

WGEServices

Customers

Customers

Accounting Policies Details Narrative [Abstract]

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'

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'

'

'

Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service

2.77%

2.86%

2.87%

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Pretax AFUDC Rate

3.36%

5.43%

7.40%

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Impairment loss

'

'

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$2,639,000

$2,600,000

$5,015,000

$2,639,000

$2,600,000

$5,015,000

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'

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$1,900,000

$500,000

$1,900,000

$500,000

$800,000

$2,600,000

$800,000

$2,600,000

$5,000,000

'

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Duration Of Cost Of Gas Recovered Or Refunded

'12 months

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Indexed Or Fixed Rate Customer Contracts Terms

'Customer contracts, which typically have terms less than 24 months, but may extend up to five years, allow WGEServices to bill customers based upon metered gas and electricity usage.

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Number of states with commercial energy systems segment activity

15

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Customer Related Information [Abstract]

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Percentage Of Total Gas Deliveries

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14.30%

78.10%

7.60%

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Number of Customers

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157,000

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162,000

Inventory Adjustments [Abstract]

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Lower Of Cost Or Market Adjustment Storage Gas Inventory

'

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($200,000)

$0

($1,400,000)

$0

$0

$0

($3,000,000)

($10,100,000)

($22,400,000)

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Accounting_Policies_Tables_Det

Accounting Policies (Tables) (Details) (USD $)	12 Months Ended
	Sep. 30, 2014		Sep. 30, 2013
Footnote Details [Abstract]	'		'
Short Term Asset Retirement Obligation	$6,000,000		$2,700,000
Schedule Of Property Plant And Equipment At Original Cost [Line Items]	'		'
Property Plant And Equipment Total Percentage	100.00%		100.00%
Regulated Operation [Member]	'		'
Schedule Of Property Plant And Equipment At Original Cost [Line Items]	'		'
Public Utilities, Property, Plant and Equipment, Transmission, Distribution and Storage	3,635,300,000		3,356,100,000
Public Utilities Property Plant And Equipment Construction Work In Progress	203,900,000		150,800,000
General, miscellaneous and intangibles	448,300,000		430,600,000
Total Property, Plant and Equipment for Segments	4,287,500,000		3,937,500,000
Transmission And Distribution Percentage	79.30%		81.50%
General, miscellaneous and intangibles percentage	9.80%		10.40%
Construction Work In Progress Percentage	4.50%		3.70%
Property Plant And Equipment Percentage for Segments	93.60%		95.60%
Unregulated Operation [Member]	'		'
Schedule Of Property Plant And Equipment At Original Cost [Line Items]	'		'
Total Property, Plant and Equipment for Segments	295,300,000		180,600,000
Property Plant And Equipment Percentage for Segments	6.40%		4.40%
WGL Holdings, Inc.	'		'
Asset Retirement Obligations Details [Line Items]	'		'
Asset Retirement Obligation, Beginning Balance	104,000,000	[1]	72,700,000
Asset Retirement Obligation, Liabilities Incurred	4,900,000		1,200,000
Asset Retirement Obligation, Liabilities Settled	-5,200,000		-1,000,000
Asset Retirement Obligation, Accretion Expense	4,400,000		3,300,000
Asset Retirement Obligation, Revision of Estimate	73,100,000	[2]	27,800,000	[2]
Asset Retirement Obligation, Ending Balance	181,200,000	[1]	104,000,000	[1]
Schedule Of Property Plant And Equipment At Original Cost [Line Items]	'		'
Property, Plant and Equipment, Gross, Total	4,582,764,000		4,118,149,000
Washington Gas Light Company	'		'
Asset Retirement Obligations Details [Line Items]	'		'
Asset Retirement Obligation, Beginning Balance	102,700,000	[1]	71,500,000
Asset Retirement Obligation, Liabilities Incurred	4,900,000		1,100,000
Asset Retirement Obligation, Liabilities Settled	-5,200,000		-1,000,000
Asset Retirement Obligation, Accretion Expense	4,300,000		3,300,000
Asset Retirement Obligation, Revision of Estimate	73,100,000	[2]	27,800,000	[2]
Asset Retirement Obligation, Ending Balance	179,800,000	[1]	102,700,000	[1]
Schedule Of Property Plant And Equipment At Original Cost [Line Items]	'		'
Property, Plant and Equipment, Gross, Total	$4,250,194,000		$3,903,482,000
[1]	Includes short-term asset retirement obligations of $6.0 million and $2.7 million for fiscal year 2014 and 2013, respectively.
[2]	WGL revised its assumptions regarding the timing and amounts related to its obligation to cut, cap and purge pipeline. The revision is primarily driven by our accelerated pipeline replacement programs.

Accounting_Policies_Operating_

Accounting Policies - Operating Leases (Details) (Leasehold Improvements [Member])	12 Months Ended
	Sep. 30, 2014
Leasehold Improvements [Member]	'
Property, Plant and Equipment [Line Items]	'
Property Plant And Equipment Depreciation Methods	'straight-line over the non-cancelable period of the lease
Property Plant And Equipment Useful Life	'15 years

Regulated_Operations_Details

Regulated Operations (Details) (USD $)	Sep. 30, 2014		Sep. 30, 2013
Asset Recoverable Gas Costs	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Liabilities, Current	$16,200,000	[1]	$23,400,000	[1]
Interruptible Sharing	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Current	3,400,000	[1]	10,700,000	[1]
Regulatory Liabilities, Current	0	[1]	1,900,000	[1]
Conservation And Rate Making Efficiency Adjustment	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Current	0	[1]	100,000	[1]
Regulatory Liabilities, Current	5,500,000	[1]	1,500,000	[1]
Plant Recovery Mechanisms	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Current	400,000		0
Regulatory Liabilities, Current	900,000		200,000
Total current	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Current	3,800,000		10,800,000
Regulatory Liabilities, Current	22,600,000		27,000,000
Accrued Asset Removal Costs	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Liability, Noncurrent	327,400,000		321,300,000
Deferred Fuel Costs	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	191,300,000	[1]	94,000,000	[1]
Other post-retirement benefits	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	0	[2]	700,000	[2]
Deferred pension costs/income-trackers	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	45,100,000	[2]	51,000,000	[2]
Unrecognized Pension Cost	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	147,900,000	[1],[3]	155,100,000	[1],[3]
Unrecognized Other Post Retirement Benefits	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	0	[1],[3]	33,800,000	[1],[3]
Regulatory Liability, Noncurrent	86,400,000	[1],[3]	0	[1],[3]
Total pension and other post-retirement benefits	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	193,000,000		240,600,000
Regulatory Liability, Noncurrent	86,400,000		0
Income tax-related amounts due from to customers	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	30,400,000	[4]	24,900,000	[4]
Regulatory Liability, Noncurrent	4,800,000	[4]	4,500,000	[4]
Deferred Gain (Loss) on Early Extinguishment of Debt	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	12,000,000	[1],[5]	11,600,000	[1],[5]
Regulatory Liability, Noncurrent	1,700,000	[1],[5]	600,000	[1],[5]
Deferred Gain On Sale Of Assets	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Liability, Noncurrent	1,400,000	[1]	1,700,000	[1]
Rights Of Way Fee	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	1,500,000	[1]	0	[1]
Regulatory Liability, Noncurrent	0	[1]	1,600,000	[1]
Other Costs Business Process Outsourcing	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	1,000,000	[1]	1,400,000	[1]
Non Retirement Postemployment Benefits	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	16,300,000	[1],[6]	15,400,000	[1],[6]
Deferred integrity management expenditures	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	2,700,000	[1],[7]	0	[1],[7]
Recoverable portion of abandoned LNG facility	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	5,600,000	[1]	7,900,000	[1]
Other Regulatory Expenses	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	2,100,000	[1]	4,800,000	[1]
Regulatory Liability, Noncurrent	9,700,000	[1]	5,100,000	[1]
Total Other	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	71,600,000		66,000,000
Regulatory Liability, Noncurrent	17,600,000		13,500,000
Total Deferred	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	455,900,000		400,600,000
Regulatory Liability, Noncurrent	431,400,000		334,800,000
Total	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets	459,700,000		411,400,000
Regulatory Liabilities	$454,000,000		$361,800,000
[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]	Relates to the District of Columbia jurisdiction.
[3]	Refer to Note 10-Pension and Other Post-Retirement Benefit Plans for a further discussion of these amounts.
[4]	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.
[5]	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.
[6]	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.
[7]	This balance represents amounts for deferred expenditures associated with Washington Gas' Distribution Integrity Management Program (DIMP) in Virginia.

Accounts_Payable_and_Other_Acc2

Accounts Payable and Other Accrued Liabilities (Details) (USD $)	Sep. 30, 2014	Sep. 30, 2013
WGL Holdings, Inc.	'	'
Accounts payable - trade	$278,800,000	$216,300,000
Employee benefits and payroll accruals	19,800,000	23,400,000
Embedded derivatives and other accrued liabilities	14,600,000	30,900,000
Accounts Payable and Accrued Liabilities, Current, Total	313,221,000	270,658,000
Washington Gas Light Company	'	'
Accounts payable - trade	146,400,000	99,700,000
Employee benefits and payroll accruals	18,200,000	21,400,000
Embedded derivatives and other accrued liabilities	11,900,000	11,700,000
Accounts Payable and Accrued Liabilities, Current, Total	$176,467,000	$132,814,000

ShortTerm_Debt_Details

Short-Term Debt (Details) (USD $)	Sep. 30, 2014		Sep. 30, 2013
Line Of Credit Facility [Line Items]	'		'
Unsecured revolving credit facility	$800,000,000	[1]	$800,000,000	[1]
Less: Commercial Paper	453,500,000		373,100,000
Net committed credit available	346,500,000		426,900,000
Short-term debt weighted average interest rate	0.19%		0.19%
Ratio Of Indebtedness To Net Capital Percentage	65.00%		'
Outstanding bank loans	0		0
Maximum [Member]	'		'
Line Of Credit Facility [Line Items]	'		'
Ratio of Indebtedness to Net Capital	1		'
Minimum [Member]	'		'
Line Of Credit Facility [Line Items]	'		'
Ratio of Indebtedness to Net Capital	0.65		'
WGL Holdings, Inc.	'		'
Footnote Details [Abstract]	'		'
Revolving credit facility maximum borrowing capacity	550,000,000		550,000,000
Revolving credit facility additional borrowings	100,000,000		100,000,000
Line Of Credit Facility [Line Items]	'		'
Less: Commercial Paper	453,500,000		373,100,000
Washington Gas Light Company	'		'
Footnote Details [Abstract]	'		'
Revolving credit facility maximum borrowing capacity	450,000,000		450,000,000
Revolving credit facility additional borrowings	100,000,000		100,000,000
Line Of Credit Facility [Line Items]	'		'
Unsecured revolving credit facility	350,000,000	[1]	350,000,000	[1]
Less: Commercial Paper	89,000,000		124,500,000
Net committed credit available	261,000,000		225,500,000
Short-term debt weighted average interest rate	0.13%		0.13%
Non Utility [Member]	'		'
Line Of Credit Facility [Line Items]	'		'
Unsecured revolving credit facility	450,000,000	[1],[2]	450,000,000	[1],[2]
Less: Commercial Paper	364,500,000	[2]	248,600,000	[2]
Net committed credit available	$85,500,000	[2]	$201,400,000	[2]
Short-term debt weighted average interest rate	0.20%		0.21%
[1]	Both WGL and Washington Gas have the right to request extensions with the banksb approval. WGLbs revolving credit facility permits it to borrow an additional $100 million, with the banksb approval, for a total of $550 million. Washington Gasb revolving credit facility permits it to borrow an additional $100 million, with the banksb approval, for a total of $450 million.
[2]	WGL Holdings includes all subsidiaries other than Washington Gas Light Company.

Long_Term_Debt_Narrative_Detai

Long Term Debt (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Long Term Debt Narrative [Abstract]	'	'
Medium Term Notes	$691	$583
Long Term Debt Weighted Average Interest Rate	5.65%	5.91%
Shelf Registration	'On August 18, 2014, WGL entered into an Indenture with The Bank of New York Mellon (the "Trustee") to issue an unlimited amount of debt securities. Supplemental indentures will supplement the Indenture and establish the respective terms of the notes. The offering of the notes has been registered under a shelf registration statement on Form S-3. At September 30, 2014, Washington Gas had the capacity under a shelf registration to issue up to $275.0 million of additional MTNs.	'
Mortgage Debt Outstanding	$0	$0

LongTerm_Debt_Maturities_Detai

Long-Term Debt - Maturities (Details) (USD $)	Sep. 30, 2014
Footnote Details [Abstract]	'
Unamortized Discount on Long Term Debt Maturities	$121,567
Statement [Line Items]	'
2015	20,000,000	[1]
2016	25,000,000	[1]
2017	0	[1]
2018	0	[1]
2019	50,000,000	[1]
Thereafter	596,000,000	[1]
Total (before project debt financing)	691,000,000	[1]
Long Term Debt Project Financing	8,300,000	[1],[2]
Total	699,300,000	[1]
Less-current maturities	20,000,000	[1]
Total non-current	679,300,000	[1]
Medium-term Notes [Member]	'
Statement [Line Items]	'
2015	20,000,000	[1]
2016	25,000,000	[1]
2017	0	[1]
2018	0	[1]
2019	50,000,000	[1]
Thereafter	596,000,000	[1]
Total (before project debt financing)	691,000,000	[1]
Long Term Debt Project Financing	0	[1],[2]
Total	691,000,000	[1]
Less-current maturities	20,000,000	[1]
Total non-current	671,000,000	[1]
Other Long Term Debt [Member]	'
Statement [Line Items]	'
Long Term Debt Project Financing	8,300,000	[1],[2]
Total	8,300,000	[1]
Less-current maturities	0	[1]
Total non-current	$8,300,000	[1]
[1]	Excludes unamortized discounts of $121,567 at September 30, 2014.
[2]	Project debt financing is anticipated to be a non-cash extinguishment. Refer to Note 13 - Commitments and Contingencies for further discussion of this construction project financing.

Long_Term_Debt_Issuances_and_R

Long Term Debt - Issuances and Retirements (Details) (USD $)	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014		Sep. 30, 2014
In Millions, unless otherwise specified	Issuances [Member]	Issuances [Member]	Retirements [Member]	Retirements [Member]	7-Nov-13	10-Sep-14	5-Dec-13		12-Sep-14
					Retirements [Member]	Retirements [Member]	Issuances [Member]		Issuances [Member]
Issuance and Retirements [Line Items]	'	'	'	'	'	'	'		'
Principal	$175	$0	$67	$0	$37	$30	$75		$100
Nominal Maturity Date	'	'	'	'	7-Nov-13	10-Sep-14	15-Dec-43		15-Sep-44
Interest Rate	'	'	'	'	4.88%	5.17%	5.00%	[1]	4.22%	[2]
Footnote Details [Abstract]	'	'	'	'	'	'	'		'
Estimated Effective Interest Rate	'	'	'	'	'	'	4.95%		4.27%
[1]	The estimated effective cost of the issued notes, including consideration of issuances fees and hedge costs, is 4.95%.
[2]	The estimated effective cost of the issued notes, including consideration of issuances fees and hedge costs, is 4.27%.

Common_Stock_Details

Common Stock (Details)	Sep. 30, 2014		Sep. 30, 2013
Common Stock Details Narrative [Abstract]	'		'
Common Stock, Shares, Outstanding	50,656,553		51,774,204
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]	'		'
Omnibus Incentive Compensation Plan	999,443	[1]	'
Dividend Reinvestment and Common Stock Purchase Plan	2,849,012		'
Employee Savings Plans	637,196		'
Directors' Stock Compensation Plan	96,650		'
Total Common Stock Reserves Shares	4,582,301		'
Footnote Details [Abstract]	'		'
Incentive Compensation Plan Stock Options	5,318		'
Performance Shares	301,378		'
[1]	In MarchB 2007, WGL adopted a shareholder-approved Omnibus Incentive Compensation Plan to replace on a prospective basis the 1999 Incentive Compensation Plan. Included are shares that may be issued which would reduce the number of shares authorized under the Omnibus Incentive Compensation Plan. These shares include 301,378B shares dedicated to performance shares granted but not vested and include 5,318 shares dedicated to stock options issued but not exercised. Refer to Note 11 - Stock-Based Compensation for a discussion regarding our stock-based compensation plans.

Preferred_Stock_Details

Preferred Stock (Details) (Washington Gas Light Company, USD $)	Sep. 30, 2014	Sep. 30, 2013
Series One [Member]	'	'
Preferred Stock, Par or Stated Value Per Share	$4.80	$4.80
Preferred Stock, Shares Outstanding	150,000	150,000
Preferred Stock, Liquidation Preference Per Share Involuntary	$100	'
Preferred Stock Liquidation Preference Voluntary	$101	'
Preferred Stock, Redemption Price Per Share	$101	'
Series Two [Member]	'	'
Preferred Stock, Par or Stated Value Per Share	$4.25	$4.25
Preferred Stock, Shares Outstanding	70,600	70,600
Preferred Stock, Liquidation Preference Per Share Involuntary	$100	'
Preferred Stock Liquidation Preference Voluntary	$105	'
Preferred Stock, Redemption Price Per Share	$105	'
Series Three [Member]	'	'
Preferred Stock, Par or Stated Value Per Share	$5	$5
Preferred Stock, Shares Outstanding	60,000	60,000
Preferred Stock, Liquidation Preference Per Share Involuntary	$100	'
Preferred Stock Liquidation Preference Voluntary	$102	'
Preferred Stock, Redemption Price Per Share	$102	'

Earnings_Per_Share_Details

Earnings Per Share (Details) (WGL Holdings, Inc., USD $)	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
WGL Holdings, Inc.	'	'	'	'	'	'	'	'	'	'	'
Earnings Per Share Disclosure [Line Items]	'	'	'	'	'	'	'	'	'	'	'
NET INCOME (LOSS) APPLICABLE TO COMMON STOCK	$38,038	($11,940)	$61,213	$18,629	($51,625)	($10,015)	$89,505	$52,388	$105,940	$80,253	$139,818
Average common shares outstanding-basic	'	'	'	'	'	'	'	'	51,759,000	51,697,000	51,522,000
Basic	$0.74	($0.23)	$1.18	$0.36	($1)	($0.19)	$1.73	$1.01	$2.05	$1.55	$2.71
Stock-based compensation plan	'	'	'	'	'	'	'	'	11	111	67
Total average common shares outstanding diluted	'	'	'	'	'	'	'	'	51,770,000	51,808,000	51,589,000
Diluted EPS	$0.74	($0.23)	$1.18	$0.36	($1)	($0.19)	$1.73	$1.01	$2.05	$1.55	$2.71

Income_Taxes_Narrative_Details

Income Taxes (Narrative) (Details) (Washington Gas Light Company, USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2010
Washington Gas Light Company	'	'	'	'
Tax savings realized from tax sharing agreement	$2.90	$1.30	$0.30	'
Increase In Regulatory Assets For Recovery Of Increased Taxes	'	'	'	42.2
Unrecognized Tax Benefits, Period Increase (Decrease)	7.6	'	'	'
Interest Expense For Uncertain Tax Position	0	0	-1.6	'
Effective Income Tax Rate, Continuing Operations	32.58%	37.93%	39.47%	'
Tax expense related to the Patient Protection and Affordable Care Act	'	'	'	$0

Income_Taxes_Components_of_Inc

Income Taxes (Components of Income Tax Expense) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
WGL Holdings, Inc.	'	'	'
Current:	'	'	'
Federal	$29,976	$41,425	($13,188)
State	5,149	11,258	-30
Current Income Tax Expense (Benefit), Total	35,125	52,683	-13,218
Deferred	'	'	'
Deferred Income Tax Expense (Benefit), Total	25,795	1,431	107,699
Amortization of investment tax credits	-3,666	-1,822	-1,132
Income Tax Expense (Benefit), Continuing Operations, Total	57,254	52,292	93,349
Washington Gas Light Company	'	'	'
Current:	'	'	'
Federal	37,098	40,492	-13,155
State	4,262	7,515	-3,332
Current Income Tax Expense (Benefit), Total	41,360	48,007	-16,487
Deferred	'	'	'
Deferred Income Tax Expense (Benefit), Total	7,050	-2,915	89,132
Amortization of investment tax credits	-876	-895	-898
Income Tax Expense (Benefit), Continuing Operations, Total	47,534	44,197	71,747
Accelerated Depreciation [Member] | WGL Holdings, Inc.	'	'	'
Deferred	'	'	'
Federal	35,747	33,394	45,506
State	9,822	6,795	9,412
Accelerated Depreciation [Member] | Washington Gas Light Company	'	'	'
Deferred	'	'	'
Federal	34,833	34,518	45,661
State	9,540	6,770	9,423
Other Federal [Member] | WGL Holdings, Inc.	'	'	'
Deferred	'	'	'
Federal	-18,014	-31,173	44,727
State	-1,760	-7,585	8,054
Other Federal [Member] | Washington Gas Light Company	'	'	'
Deferred	'	'	'
Federal	-30,523	-35,982	27,851
State	($6,800)	($8,221)	$6,197

Income_Taxes_Tax_Rate_Reconcil

Income Taxes (Tax Rate Reconciliation) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
WGL Holdings, Inc.	'	'	'
Income taxes at statutory federal tax rate	$57,580	$46,853	$82,070
Accelerated depreciation less amount deferred	1,875	2,106	1,178
Amortization of investment tax credits	-3,666	-1,822	-1,132
Cost Of Removal	-4,902	-2,356	-2,291
State income taxes-net of federal benefit	8,734	7,448	12,068
Medicare D subsidy	3,621	0	-2,827
Other items-net	1,254	63	-1,371
Income Tax Expense (Benefit), Continuing Operations, Total	57,254	52,292	93,349
Statutory federal income tax rate (%)	35.00%	35.00%	35.00%
Accelerated depreciation less amount deferred (%)	1.14%	1.57%	0.50%
Amortization of investment tax credits (%)	-2.23%	-1.36%	-0.48%
Cost of removal (%)	-2.98%	-1.76%	-0.98%
State income taxes-net of federal benefit (%)	5.31%	5.56%	5.15%
Medicare D adjustment (%)	-2.20%	0.00%	1.21%
Other items-net (%)	0.76%	0.05%	-0.59%
Effective Income Tax Rate, Continuing Operations, Total	34.80%	39.06%	39.81%
Washington Gas Light Company	'	'	'
Income taxes at statutory federal tax rate	51,050	40,782	63,628
Accelerated depreciation less amount deferred	1,875	2,106	1,178
Amortization of investment tax credits	-876	-895	-898
Cost Of Removal	-4,902	-2,356	-2,291
State income taxes-net of federal benefit	6,711	5,487	8,916
Consolidated tax sharing allocation	-2,862	-1,290	-309
Medicare D subsidy	3,621	0	-2,827
Other items-net	159	363	-1,304
Income Tax Expense (Benefit), Continuing Operations, Total	$47,534	$44,197	$71,747
Statutory federal income tax rate (%)	35.00%	35.00%	35.00%
Accelerated depreciation less amount deferred (%)	1.29%	1.81%	0.65%
Amortization of investment tax credits (%)	-0.60%	-0.77%	-0.49%
Cost of removal (%)	-3.36%	-2.02%	-1.26%
State income taxes-net of federal benefit (%)	4.60%	4.71%	4.90%
Consolidated tax sharing allocation (%)	-1.96%	-1.11%	-0.17%
Medicare D adjustment (%)	-2.48%	0.00%	1.56%
Other items-net (%)	0.09%	0.31%	-0.72%
Effective Income Tax Rate, Continuing Operations, Total	32.58%	37.93%	39.47%

Income_Taxes_Components_of_Def

Income Taxes (Components of Deferred Tax Assets) (Details) (USD $)	Sep. 30, 2014	Sep. 30, 2013
In Thousands, unless otherwise specified
Current [Member] | WGL Holdings, Inc.	'	'
Deferred Income Tax Assets:	'	'
Pensions	$0	$0
Other post-retirement benefits	0	0
Uncollectible accounts	9,268	8,127
Inventory overheads	6,591	6,431
Capital gains/losses-net	0	2
Valuation allowance	0	-2
Employee compensation and benefits	6,306	5,876
Customer advances	0	0
Derivatives	6,503	0
Deferred gas costs	0	4,911
Other	814	816
Solar grant/ investment tax credit	0	0
Total assets	29,482	26,161
Deferred Income Tax Liabilities:	'	'
Other post-retirement benefits	0	0
Accelerated depreciation and other plant related items	0	0
Losses/gains on reacquired debt	0	0
Income taxes recoverable through future rates	0	0
Deferred gas costs	2,818	0
Derivatives	0	1,639
Partnership basis difference	0	0
Total liabilities	2,818	1,639
Net accumulated deferred income tax assets (liabilities)	26,664	24,522
Current [Member] | Washington Gas Light Company	'	'
Deferred Income Tax Assets:	'	'
Pensions	0	0
Other post-retirement benefits	0	0
Uncollectible accounts	7,618	6,948
Inventory overheads	6,591	6,431
Employee compensation and benefits	5,902	5,756
Customer advances	0	0
Derivatives	4,809	2,138
Deferred gas costs	0	4,911
Other	814	816
Solar grant/ investment tax credit	0	0
Total assets	25,734	27,000
Deferred Income Tax Liabilities:	'	'
Other post-retirement benefits	0	0
Accelerated depreciation and other plant related items	0	0
Losses/gains on reacquired debt	0	0
Income taxes recoverable through future rates	0	0
Deferred gas costs	2,818	0
Derivatives	0	0
Other	0	0
Total liabilities	2,818	0
Net accumulated deferred income tax assets (liabilities)	22,916	27,000
Non-current [Member] | WGL Holdings, Inc.	'	'
Deferred Income Tax Assets:	'	'
Pensions	24,349	17,362
Other post-retirement benefits	0	18,510
Uncollectible accounts	0	0
Inventory overheads	0	0
Capital gains/losses-net	0	0
Valuation allowance	0	0
Employee compensation and benefits	37,873	37,301
Customer advances	197	197
Derivatives	31,555	7,872
Deferred gas costs	4,218	0
Other	1,225	2,530
Solar grant/ investment tax credit	39,184	17,415
Total assets	138,601	101,187
Deferred Income Tax Liabilities:	'	'
Other post-retirement benefits	38,299	0
Accelerated depreciation and other plant related items	669,040	596,754
Losses/gains on reacquired debt	1,426	1,567
Income taxes recoverable through future rates	65,374	112,222
Deferred gas costs	0	4,667
Derivatives	0	0
Partnership basis difference	25,370	15,784
Total liabilities	799,509	730,994
Net accumulated deferred income tax assets (liabilities)	-660,908	-629,807
Non-current [Member] | Washington Gas Light Company	'	'
Deferred Income Tax Assets:	'	'
Pensions	23,738	16,768
Other post-retirement benefits	0	18,474
Uncollectible accounts	0	0
Inventory overheads	0	0
Employee compensation and benefits	27,961	27,125
Customer advances	197	197
Derivatives	31,555	7,872
Deferred gas costs	4,218	0
Other	0	1,727
Solar grant/ investment tax credit	312	312
Total assets	87,981	72,475
Deferred Income Tax Liabilities:	'	'
Other post-retirement benefits	38,065	0
Accelerated depreciation and other plant related items	602,376	565,996
Losses/gains on reacquired debt	1,426	1,567
Income taxes recoverable through future rates	65,128	111,698
Deferred gas costs	0	4,667
Derivatives	0	0
Other	932	0
Total liabilities	707,927	683,928
Net accumulated deferred income tax assets (liabilities)	($619,946)	($611,453)

Income_Taxes_Unrecognized_Tax_

Income Taxes (Unrecognized Tax Benefits) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'	'	'
Total unrecognized tax benefits, beginning balance	$25,051	$22,082	$20,699
Increases resulting from current period tax positions	10,512	5,251	3,396
Decreases resulting from prior period tax positions	-2,950	-2,282	-2,013
Total unrecognized tax benefits, ending balance	$32,613	$25,051	$22,082

Recovered_Sheet1

Pension and Other Post-retirement Benefit Plans (Narrative) (Details) (USD $)	12 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Change in plan's funded status	$127,500,000		'		'
Defined Benefit Plan Accumulated Other Comprehensive Income Net Transition Assets Obligations After Tax	190,600,000		'		'
Defined Contribution Plan, Contributions by Employer	4,200,000		3,500,000		3,400,000
Defined Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year 1	0		'		'
Defined Contribution Plan Employer Discretionary Contribution Amount	1,600,000		800,000		600,000
Percentage Of Prior Years Asset Gains And Losses Recognized	20.00%		'		'
EGWP Effect On Post Retirement Benefits	500,000		'		'
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%		'		'
Defined Benefit Plan Target Allocation Percentage [Abstract]	'		'		'
US Large Cap Equities	32.50%		'		'
US Small Mid Cap Equities	4.50%		'		'
International Equities	8.00%		'		'
Fixed Income And Cash	50.00%		'		'
Real Estate Investments	5.00%		'		'
Asset Class Allocations Allowed Range Within Plus Or Minus	5.00%		'		'
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]	'		'		'
Health Care Cost Trend Rates For Medicare And Non Medicare Eligible Retirees	7.00%		7.50%		'
Future Healthcare Cost Trend Rates	5.00%		'		'
Future HRA Stipend Increase	3.00%		'		'
Maximum [Member]	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Percentage Of Supplemental Contribution	6.00%		'		'
Minimum [Member]	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Percentage Of Supplemental Contribution	4.00%		'		'
WGEServices	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Defined Contribution Plan, Contributions by Employer	'		800,000		400,000
WGL Holdings, Inc.	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Prepaid post-retirement benefits	96,385,000		0		'
Accumulated Other Comprehensive Income (Loss), Net of Tax	-7,961,000		-11,048,000		-12,201,000
Washington Gas Light Company	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Prepaid post-retirement benefits	95,660,000		0		'
Accumulated Other Comprehensive Income (Loss), Net of Tax	-6,413,000		-11,048,000		-12,201,000
Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Prepaid post-retirement benefits	0	[1]	0	[1]	'
Defined Benefit Plan Employer Payment Current Fiscal Year	0		'		'
The projected benefit obligation (PBO)	865,200,000		788,800,000		'
The projected accumulated benefit obligation (ABO)	801,900,000		737,200,000		'
Non-funded DB Serp [Member]	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Defined Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year 1	4,100,000		'		'
Defined Benefit Plan Employer Payment Current Fiscal Year	1,800,000		'		'
The projected benefit obligation (PBO)	50,700,000		47,800,000		'
The projected accumulated benefit obligation (ABO)	46,200,000		43,900,000		'
Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Prepaid post-retirement benefits	96,400,000		0		'
Defined Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year 1	16,600,000		'		'
Defined Benefit Plan Employer Payment Current Fiscal Year	16,000,000		'		'
Assumed Income Tax Rate	41.50%		'		'
Other PostretirementBenefit Plans Defined Benefit [Member] | Union Eligible Employee [Member]	'		'		'
Defined Benefit Plan Target Allocation Percentage [Abstract]	'		'		'
US Large Cap Equities	50.00%		'		'
Fixed Income And Cash	50.00%		'		'
Other PostretirementBenefit Plans Defined Benefit [Member] | Management Employee [Member]	'		'		'
Defined Benefit Plan Target Allocation Percentage [Abstract]	'		'		'
US Large Cap Equities	60.00%		'		'
Fixed Income And Cash	40.00%		'		'
Non-funded DB Serp Restoration [Member]	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
The projected benefit obligation (PBO)	1,200,000		800,000		'
The projected accumulated benefit obligation (ABO)	$700,000		$500,000		'
[1]	The DB SERP and DB Restoration, included in pension benefits in the table above, have no assets.

Recovered_Sheet2

Pension and Other Post-retirement Benefit Plans (Table 1) (Details) (USD $)	12 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
Change in plan assets	'		'		'
Fair value of plan assets at end of year	$23,800,000		$21,100,000		$18,700,000
Pension Plans Defined Benefit [Member]	'		'		'
Change in projected benefit obligation	'		'		'
Benefit obligation at beginning of year	837,400,000	[1]	937,200,000	[1]	'
Service cost	14,000,000	[1]	17,000,000	[1]	12,900,000
Interest cost	40,400,000	[1]	36,600,000	[1]	40,500,000
Change in plan benefits	0	[1]	0	[1]	'
Actuarial loss (gain)	68,600,000	[1]	-110,000,000	[1]	'
Retiree Contributions	0	[1]	0	[1]	'
Medicare part D reimbursements	0	[1]	0	[1]	'
Benefits Paid	-43,300,000	[1]	-43,400,000	[1]	'
Projected benefit obligation at end of year	917,100,000	[1]	837,400,000	[1]	937,200,000	[1]
Change in plan assets	'		'		'
Fair Value of plan assets at beginning of year	745,200,000	[1]	750,600,000	[1]	'
Actual return on plan assets	103,300,000	[1]	38,600,000	[1]	'
Company contributions	1,700,000	[1]	1,800,000	[1]	'
Retiree Contributions And Medicare Part D Reimbursements	0	[1]	0	[1]	'
Expenses	-2,200,000	[1]	-2,400,000	[1]	'
Benefits Paid	-43,300,000	[1]	-43,400,000	[1]	'
Fair value of plan assets at end of year	804,700,000	[1]	745,200,000	[1]	750,600,000	[1]
Funded status at end of year	-112,400,000	[1]	-92,200,000	[1]	'
Total Recognized	'		'		'
Non-current asset	0	[1]	0	[1]	'
Current liability	-4,200,000	[1]	-3,500,000	[1]	'
Non-current liability	-108,200,000	[1]	-88,700,000	[1]	'
Total Recognized	-112,400,000	[1]	-92,200,000	[1]	'
Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Change in projected benefit obligation	'		'		'
Benefit obligation at beginning of year	429,800,000	[2]	480,100,000		'
Service cost	7,600,000		9,600,000		8,000,000
Interest cost	18,700,000		18,800,000		25,100,000
Change in plan benefits	-136,500,000		0		'
Actuarial loss (gain)	38,200,000		-62,300,000		'
Retiree Contributions	4,400,000		3,900,000		'
Medicare part D reimbursements	500,000		700,000		'
Benefits Paid	-19,500,000		-21,000,000		'
Projected benefit obligation at end of year	343,200,000	[2]	429,800,000	[2]	480,100,000
Change in plan assets	'		'		'
Fair Value of plan assets at beginning of year	380,900,000		358,300,000		'
Actual return on plan assets	57,800,000		19,900,000		'
Company contributions	16,000,000		18,000,000		'
Retiree Contributions And Medicare Part D Reimbursements	4,400,000		5,700,000		'
Expenses	0		0		'
Benefits Paid	-19,500,000		-21,000,000		'
Fair value of plan assets at end of year	439,600,000		380,900,000		358,300,000
Funded status at end of year	96,400,000		-48,900,000		'
Total Recognized	'		'		'
Non-current asset	96,400,000		0		'
Current liability	0		0		'
Non-current liability	0		-48,900,000		'
Total Recognized	$96,400,000		($48,900,000)		'
[1]	The DB SERP and DB Restoration, included in pension benefits in the table above, have no assets.
[2]	For the Health and Life Benefits, the change in projected benefit obligation represents the accumulated benefit obligation.

Pension_and_Other_Postretireme2

Pension and Other Post-retirement Benefit Plans (Table2) (Details) (USD $)	Sep. 30, 2014	Sep. 30, 2013
In Millions, unless otherwise specified
Pension Plans Defined Benefit [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Projected benefit obligation	$865.20	$788.80
Accumulated benefit obligation	801.9	737.2
Non-funded DB Serp [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Projected benefit obligation	50.7	47.8
Accumulated benefit obligation	46.2	43.9
Non-funded DB Serp Restoration [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Projected benefit obligation	1.2	0.8
Accumulated benefit obligation	$0.70	$0.50

Pension_and_Other_Postretireme3

Pension and Other Post-retirement Benefit Plans (Table 3) (Details) (USD $)	Sep. 30, 2014		Sep. 30, 2013
In Millions, unless otherwise specified
Footnote Details [Abstract]	'		'
Accumulated Other Comprehensive Loss Tax Effect	$4.90		$7.90
Pension Plans Defined Benefit [Member]	'		'
Unrecognized Costs/Income Recorded on the Balance Sheet	'		'
Unrecognized actuarial net loss	162.6		171.1
Unrecognized prior service cost (credit)	1.2		1.3
Total	163.8		172.4
Regulatory asset	147.9		155.1
Defined Benefit Plan Recorded On Balance Sheet Before Tax	163.8		172.4
Footnote Details [Abstract]	'		'
Accumulated Other Comprehensive Loss Tax Effect	15.9	[1]	17.3	[1]
Other PostretirementBenefit Plans Defined Benefit [Member]	'		'
Unrecognized Costs/Income Recorded on the Balance Sheet	'		'
Unrecognized actuarial net loss	50.1		55.3
Unrecognized prior service cost (credit)	-149.3		-22.4
Total	-99.2		32.9
Regulatory asset	-94.6		31.3
Defined Benefit Plan Recorded On Balance Sheet Before Tax	-99.2		32.9
Footnote Details [Abstract]	'		'
Accumulated Other Comprehensive Loss Tax Effect	($4.60)	[1]	$1.60	[1]
[1]	The total amount of accumulated other comprehensive loss recorded on our balance sheets at SeptemberB 30, 2014 and 2013 is net of an income tax benefit of $4.9B million and $7.9B million, respectively.

Pension_and_Other_Postretireme4

Pension and Other Post-retirement Benefit Plans (Table 4) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014
Pension Plans Defined Benefit [Member] | Regulatory Assets Liabilities [Member]	'
Amounts Recognized During Fiscal Year	'
Actuarial net loss	$15.50
Prior service cost (credit)	0.2
Total	15.7
Amounts to be Recognized During Fiscal Year	'
Actuarial net loss	17.1
Prior service cost (credit)	0.2
Total	17.3
Pension Plans Defined Benefit [Member] | Accumulated Other Comprehensive Loss	'
Amounts Recognized During Fiscal Year	'
Actuarial net loss	1.3
Prior service cost (credit)	0.1
Total	1.4
Amounts to be Recognized During Fiscal Year	'
Actuarial net loss	1.7
Prior service cost (credit)	0.1
Total	1.8
Other PostretirementBenefit Plans Defined Benefit [Member] | Regulatory Assets Liabilities [Member]	'
Amounts Recognized During Fiscal Year	'
Actuarial net loss	4.8
Prior service cost (credit)	-9.1
Total	-4.3
Amounts to be Recognized During Fiscal Year	'
Actuarial net loss	4.2
Prior service cost (credit)	-14.5
Total	-10.3
Other PostretirementBenefit Plans Defined Benefit [Member] | Accumulated Other Comprehensive Loss	'
Amounts Recognized During Fiscal Year	'
Actuarial net loss	0.3
Prior service cost (credit)	-0.5
Total	-0.2
Amounts to be Recognized During Fiscal Year	'
Actuarial net loss	0.2
Prior service cost (credit)	-0.7
Total	($0.50)

Pension_and_Other_Postretireme5

Pension and Other Post-retirement Benefit Plans (Table 5) (Details) (USD $)	12 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
WGL Holdings, Inc.	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Recognized prior service cost	$6,095,000	[1],[2]	($1,671,000)	[1]	($640,000)
Recognized actuarial loss	-1,594,000	[1]	-3,399,000	[1]	2,125,000
Change in transition obligation	0	[1]	238,000	[1]	239,000
Washington Gas Light Company	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Recognized prior service cost	6,095,000	[1],[2]	-1,671,000	[1]	-640,000
Recognized actuarial loss	-1,594,000	[1]	-3,399,000	[1]	2,125,000
Change in transition obligation	0	[1]	238,000	[1]	239,000
Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Service cost	14,000,000	[3]	17,000,000	[3]	12,900,000
Interest cost	40,400,000	[3]	36,600,000	[3]	40,500,000
Expected return on plan assets	-41,000,000		-41,900,000		-43,500,000
Recognized prior service cost	300,000		1,000,000		1,000,000
Recognized actuarial loss	16,800,000		28,700,000		16,100,000
Change in transition obligation	0		0		0
Net periodic benefit cost	30,500,000		41,400,000		27,000,000
Amount allocated to construction projects	-4,300,000		-5,700,000		-3,400,000
Amount deferred as regulatory asset (liability)-net	7,000,000		-3,700,000		-7,500,000
Amount charged (credited) to expense	33,200,000		32,000,000		16,100,000
Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Service cost	7,600,000		9,600,000		8,000,000
Interest cost	18,700,000		18,800,000		25,100,000
Expected return on plan assets	-19,300,000		-18,300,000		-18,800,000
Recognized prior service cost	-9,600,000		-3,900,000		-3,900,000
Recognized actuarial loss	5,000,000		9,200,000		13,300,000
Change in transition obligation	0		1,100,000		1,100,000
Net periodic benefit cost	2,400,000		16,500,000		24,800,000
Amount allocated to construction projects	-400,000		-2,800,000		-3,700,000
Amount deferred as regulatory asset (liability)-net	-2,300,000		2,400,000		1,500,000
Amount charged (credited) to expense	($300,000)		$16,100,000		$22,600,000
[1]	(a) These accumulated other comprehensive income components are included in the computation of net periodic benefit cost. Refer to Note 10-Pension and other post-retirement benefit plans for additional details.
[2]	(b) The majority of the 2014 change to the prior service cost component of other comprehensive income is related to the impact of the OPEB plan amendment and re-measurement. Refer to Note 10-Pension and other post-retirement benefit plans for additional details.
[3]	The DB SERP and DB Restoration, included in pension benefits in the table above, have no assets.

Pension_and_Other_Postretireme6

Pension and Other Post-retirement Benefit Plans (Table 6) (Details)	12 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
Pension Plans Defined Benefit [Member]	'		'		'
Net Periodic Benefit Cost Assumptions [Abstract]	'		'		'
Discount rate	'		4.00%	[1]	5.30%	[1]
Expected long-term return on plan assets	6.50%		6.75%		7.50%
Pension Plans Defined Benefit [Member] | Maximum [Member]	'		'		'
Benefit Obligations Assumptions [Abstract]	'		'		'
Discount rate	4.40%	[2]	5.00%	[2]	'
Rate of compensation increase	4.10%		5.15%		'
Net Periodic Benefit Cost Assumptions [Abstract]	'		'		'
Discount rate	5.00%	[1]	'		'
Rate of compensation increase	5.15%	[3]	5.15%	[3]	5.15%	[3]
Pension Plans Defined Benefit [Member] | Minimum [Member]	'		'		'
Benefit Obligations Assumptions [Abstract]	'		'		'
Discount rate	4.00%	[2]	4.50%	[2]	'
Rate of compensation increase	3.50%		3.85%		'
Net Periodic Benefit Cost Assumptions [Abstract]	'		'		'
Discount rate	4.50%	[1]	'		'
Rate of compensation increase	3.85%	[3]	3.85%	[3]	3.85%	[3]
Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Benefit Obligations Assumptions [Abstract]	'		'		'
Discount rate	4.40%	[2]	5.10%	[2]	'
Rate of compensation increase	4.10%		3.85%		'
Net Periodic Benefit Cost Assumptions [Abstract]	'		'		'
Discount rate	'		4.00%	[1]	5.10%	[1]
Expected long-term return on plan assets	6.25%	[4]	6.75%	[4]	7.40%	[4]
Rate of compensation increase	3.85%	[3]	3.85%	[3]	'
Other PostretirementBenefit Plans Defined Benefit [Member] | Maximum [Member]	'		'		'
Net Periodic Benefit Cost Assumptions [Abstract]	'		'		'
Discount rate	5.10%	[1]	'		'
Rate of compensation increase	'		'		5.15%	[3]
Other PostretirementBenefit Plans Defined Benefit [Member] | Minimum [Member]	'		'		'
Net Periodic Benefit Cost Assumptions [Abstract]	'		'		'
Discount rate	4.60%	[1]	'		'
Rate of compensation increase	'		'		3.85%	[3]
[1]	The changes in the discount rates over the last two fiscal years primarily reflects the changes in long-term interest rates.
[2]	The decrease in the discount rate in fiscal year 2014 compared to prior years primarily reflects the decrease in long-term interest rates.
[3]	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.
[4]	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 41.5%.

Pension_and_Other_Postretireme7

Pension and Other Post-retirement Benefit Plans (Table 7) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]	'
Increase one percentage point total service and interest cost components	$3.60
Decrease one percentage point total service and interest cost components	-2.7
Increase one percentage point post-retirement benefit obligation	10.5
Decrease one percentage point post-retirement benefit obligation	($9.20)

Pension_and_Other_Postretireme8

Pension and Other Post-retirement Benefit Plans (Table 8) (Details) (USD $)	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
In Millions, unless otherwise specified
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan assets at end of year	$23.80		$21.10		$18.70
Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	803.7		748.4		'
Receivable (Payable)	1	[1]	-3.2	[1]	'
Fair value of plan assets at end of year	804.7	[2]	745.2	[2]	750.6	[2]
Percentage of fair value of plan investments	99.90%		100.40%		'
Percent Receivable (Payable)	0.10%	[1]	-0.40%	[1]	'
Total plan assets percent	100.00%		100.00%		'
Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	439.8		379.8		'
Receivable (Payable)	-0.2		1.1		'
Fair value of plan assets at end of year	439.6		380.9		358.3
Percentage of fair value of plan investments	100.00%		99.70%		'
Percent Receivable (Payable)	0.00%		0.30%		'
Total plan assets percent	100.00%		100.00%		'
Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	32.9		32.4		'
Level 1 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0.8		0.6		'
Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	747		694.9		'
Level 2 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	439		379.2		'
Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	23.8		21.1		'
Level 3 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Cash and Cash Equivalents [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0.6		0.9		'
Percentage of fair value of plan investments	0.10%		0.10%		'
Cash and Cash Equivalents [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0.8		0.6		'
Percentage of fair value of plan investments	0.20%		0.20%		'
Cash and Cash Equivalents [Member] | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0.6		0.9		'
Cash and Cash Equivalents [Member] | Level 1 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0.8		0.6		'
Cash and Cash Equivalents [Member] | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Cash and Cash Equivalents [Member] | Level 2 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Cash and Cash Equivalents [Member] | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Cash and Cash Equivalents [Member] | Level 3 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Equity Securities US Small Cap [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	32.3		31.5		'
Percentage of fair value of plan investments	4.00%		4.20%		'
Equity Securities US Small Cap [Member] | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	32.3		31.5		'
Equity Securities US Small Cap [Member] | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Equity Securities US Small Cap [Member] | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Equity Securities Preferred [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0.1		0.1		'
Percentage of fair value of plan investments	0.00%		0.00%		'
Equity Securities Preferred [Member] | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Equity Securities Preferred [Member] | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0.1		0.1		'
Equity Securities Preferred [Member] | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
US Treasury Securities [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	110.6		124.5		'
Percentage of fair value of plan investments	13.80%		16.70%		'
US Treasury Securities [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	25.6		23.6		'
Percentage of fair value of plan investments	5.80%		6.20%		'
US Treasury Securities [Member] | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
US Treasury Securities [Member] | Level 1 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
US Treasury Securities [Member] | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	110.6		124.5		'
US Treasury Securities [Member] | Level 2 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	25.6		23.6		'
US Treasury Securities [Member] | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
US Treasury Securities [Member] | Level 3 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
US Government Agencies Debt Securities [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	2		1.7		'
Percentage of fair value of plan investments	0.50%		0.40%		'
US Government Agencies Debt Securities [Member] | Level 1 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
US Government Agencies Debt Securities [Member] | Level 2 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	2		1.7		'
US Government Agencies Debt Securities [Member] | Level 3 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
U S Government Agencies And Sponsored Entities Debt Securities [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	24.6		19		'
Percentage of fair value of plan investments	3.00%		2.50%		'
U S Government Agencies And Sponsored Entities Debt Securities [Member] | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
U S Government Agencies And Sponsored Entities Debt Securities [Member] | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	24.6		19		'
U S Government Agencies And Sponsored Entities Debt Securities [Member] | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Domestic Corporate Debt Securities [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	108.4		93.6		'
Percentage of fair value of plan investments	13.50%		12.60%		'
Domestic Corporate Debt Securities [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	34		28.7		'
Percentage of fair value of plan investments	7.70%		7.50%		'
Domestic Corporate Debt Securities [Member] | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Domestic Corporate Debt Securities [Member] | Level 1 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Domestic Corporate Debt Securities [Member] | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	108.4		93.6		'
Domestic Corporate Debt Securities [Member] | Level 2 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	34		28.7		'
Domestic Corporate Debt Securities [Member] | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Domestic Corporate Debt Securities [Member] | Level 3 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Asset-backed Securities [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	1.8		1.9		'
Percentage of fair value of plan investments	0.20%		0.20%		'
Asset-backed Securities [Member] | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Asset-backed Securities [Member] | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	1.8		1.9		'
Asset-backed Securities [Member] | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Municipalities | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	9.2		9		'
Percentage of fair value of plan investments	1.10%		1.20%		'
Municipalities | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	4.8		4.1		'
Percentage of fair value of plan investments	1.10%		1.10%		'
Municipalities | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Municipalities | Level 1 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Municipalities | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	9.2		9		'
Municipalities | Level 2 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	4.8		4.1		'
Municipalities | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Municipalities | Level 3 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Foreign Corporate Debt Securities [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	23.8		18.4		'
Percentage of fair value of plan investments	3.00%		2.50%		'
Foreign Corporate Debt Securities [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	5.7		4.6		'
Percentage of fair value of plan investments	1.30%		1.20%		'
Foreign Corporate Debt Securities [Member] | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Foreign Corporate Debt Securities [Member] | Level 1 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Foreign Corporate Debt Securities [Member] | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	23.8		18.4		'
Foreign Corporate Debt Securities [Member] | Level 2 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	5.7		4.6		'
Foreign Corporate Debt Securities [Member] | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Foreign Corporate Debt Securities [Member] | Level 3 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0		0		'
Repurchase Agreements [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	2.5	[3]	1	[3]	'
Percentage of fair value of plan investments	0.30%	[3]	0.10%	[3]	'
Repurchase Agreements [Member] | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[3]	0	[3]	'
Repurchase Agreements [Member] | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	2.5	[3]	1	[3]	'
Repurchase Agreements [Member] | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[3]	0	[3]	'
Fixed Income Securities Other [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	7	[4]	5.7	[4]	'
Percentage of fair value of plan investments	0.80%	[4]	0.80%	[4]	'
Fixed Income Securities Other [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	5.3	[5]	5.3	[5]	'
Percentage of fair value of plan investments	1.20%	[5]	1.40%	[5]	'
Fixed Income Securities Other [Member] | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[4]	0	[4]	'
Fixed Income Securities Other [Member] | Level 1 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[5]	0	[5]	'
Fixed Income Securities Other [Member] | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	7	[4]	5.7	[4]	'
Fixed Income Securities Other [Member] | Level 2 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	5.3	[5]	5.3	[5]	'
Fixed Income Securities Other [Member] | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[4]	0	[4]	'
Fixed Income Securities Other [Member] | Level 3 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[5]	0	[5]	'
Mutual Funds [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	112.4	[6]	93.2	[6]	'
Percentage of fair value of plan investments	14.00%	[6]	12.50%	[6]	'
Mutual Funds [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	1.9	[7]	'		'
Percentage of fair value of plan investments	0.40%	[7]	'		'
Mutual Funds [Member] | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[6]	0	[6]	'
Mutual Funds [Member] | Level 1 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[7]	'		'
Mutual Funds [Member] | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	112.4	[6]	93.2	[6]	'
Mutual Funds [Member] | Level 2 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	1.9	[7]	'		'
Mutual Funds [Member] | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[6]	0	[6]	'
Mutual Funds [Member] | Level 3 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[7]	'		'
Commingled Funds [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	359.7	[8]	311.2	[8]	'
Percentage of fair value of plan investments	81.80%	[8]	81.70%	[8]	'
Commingled Funds [Member] | Level 1 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[8]	0	[8]	'
Commingled Funds [Member] | Level 2 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	359.7	[8]	311.2	[8]	'
Commingled Funds [Member] | Level 3 [Member] | Other PostretirementBenefit Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[8]	0	[8]	'
Commingled Funds And Pooled Separate Accounts [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	340	[9]	316.6	[9]	'
Percentage of fair value of plan investments	42.30%	[9]	42.50%	[9]	'
Commingled Funds And Pooled Separate Accounts [Member] | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[9]	0	[9]	'
Commingled Funds And Pooled Separate Accounts [Member] | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	316.2	[9]	295.5	[9]	'
Commingled Funds And Pooled Separate Accounts [Member] | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	23.8	[9]	21.1	[9]	'
Private Equity / Limited Partnership | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	30.5	[10]	33.3	[10]	'
Percentage of fair value of plan investments	3.80%	[10]	4.50%	[10]	'
Private Equity / Limited Partnership | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[10]	0	[10]	'
Private Equity / Limited Partnership | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	30.5	[10]	33.3	[10]	'
Private Equity / Limited Partnership | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[10]	0	[10]	'
Futures Contract [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	-0.1	[11]	-0.3	[11]	'
Percentage of fair value of plan investments	0.00%	[11]	0.00%	[11]	'
Futures Contract [Member] | Level 1 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	0	[11]	0	[11]	'
Futures Contract [Member] | Level 2 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	-0.1	[11]	-0.3	[11]	'
Futures Contract [Member] | Level 3 [Member] | Pension Plans Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'		'		'
Fair value of plan investments	$0	[11]	$0	[11]	'
[1]	At September 30, 2014, this receivable represents a pending trade for investment sales. At September 30, 2013, this payable represents a pending trade for investment purchases.
[2]	The DB SERP and DB Restoration, included in pension benefits in the table above, have no assets.
[3]	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.
[4]	This category primarily includes Yankee bonds and non-U.S. government bonds.
[5]	At September 30, 2014 and 2013, this category consisted primarily of 82% non-U.S. government bonds and 18% Yankee bonds.
[6]	At September 30, 2014 and September 30, 2013, investments in mutual funds consisted primarily of corporate fixed income instruments.
[7]	At September 30, 2014, investments in mutual funds consisted primarily of 63% short-term obligations consisting of certificates of deposit and time deposits, 23% high-quality commercial paper, 6% repurchase agreements, 4% corporate notes of U.S. and foreign corporations and 4% U.S. governmental and U.S. agency securities.
[8]	At September 30, 2014 and 2013, investments in commingled funds consisted primarily of 66% common stock of large-cap U.S. companies, 17% U.S. agency obligations and government sponsored entities and 17% corporate bonds.
[9]	At September 30, 2014, investments in commingled funds and pooled separate accounts consisted primarily of 75% common stock of large-cap U.S. companies; 14% income producing properties located in the United States; 9% equity securities of non-U.S. companies; and 2% short-term money market investments. At September 30, 2013, investments in commingled funds and pooled separate accounts consisted primarily of 67% common stock of large-cap U.S. companies; 12% income producing properties located in the United States; 20% equity securities of non-U.S. companies; and 1% short-term money market investments.
[10]	At September 30, 2014, investments in private equity/limited partnership consisted of common stock of international companies.
[11]	At September 30, 2014, this category includes long-term U.S. Treasury interest rate futures contracts and interest rate put options.

Pension_and_Other_Postretireme9

Pension and Other Post-retirement Benefit Plans (Table 8-Footnotes) (Details)	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Large Cap U.S. Companies Common Stock [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Allocation of investments in comingled funds and pooled separate accounts	75.00%	67.00%
Allocation of investments in comingled funds	66.00%	66.00%
Income Producing Properties [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Allocation of investments in comingled funds and pooled separate accounts	14.00%	12.00%
Foreign Company Stock [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Allocation of investments in comingled funds and pooled separate accounts	9.00%	20.00%
Short-term money market investments [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Allocation of investments in comingled funds and pooled separate accounts	2.00%	1.00%
Certificates of deposit and time deposits [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Allocation of investments in mutual funds	63.00%	'
High-quality commercial paper [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Allocation of investments in mutual funds	23.00%	'
Repurchase Agreements [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Allocation of investments in mutual funds	6.00%	'
Corporate notes of U.S. and foreign corporations [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Allocation of investments in mutual funds	4.00%	'
U.S. governmental and U.S. agency securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Allocation of investments in mutual funds	4.00%	'
Foreign Corporate Debt Securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Allocation of investments in other securities	82.00%	82.00%
Yankee Bonds [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Allocation of investments in other securities	18.00%	18.00%
U.S. agency obligations and government [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Allocation of investments in comingled funds	17.00%	17.00%
Corporate Bonds	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Allocation of investments in comingled funds	17.00%	17.00%

Recovered_Sheet3

Pension and Other Post-retirement Benefit Plans (Table 9) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Changes in fair value of the Level 3 assets [Abstract]	'	'
Fair Value of plan assets at beginning of year	$21.10	$18.70
Assets still held at year end	2.7	2.4
Fair value of plan assets at end of year	$23.80	$21.10

Recovered_Sheet4

Pension and Other Post-retirement Benefit Plans (Table 10) (Details) (USD $)	Sep. 30, 2014
In Millions, unless otherwise specified
Pension Plans Defined Benefit [Member]	'
Expected Benefit Payments [Abstract]	'
2015	$48.90
2016	50.3
2017	51.9
2018	53
2019	54.7
2020-2024	286.5
Other PostretirementBenefit Plans Defined Benefit [Member]	'
Expected Benefit Payments [Abstract]	'
2015	17.9
2016	18.8
2017	19.4
2018	20.1
2019	20.6
2020-2024	$105.30

Share_Based_Compensation_Narra

Share Based Compensation (Narrative) (Details) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013	Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'
Compensation expense recognized	$3.40		$6.50	$3.60
Unrecognized compensation expense	6.5		'	'
Weighted-average period remaining to recognize unrecognized compensation expense	'1 year 8 months		'	'
Tax benefit from compensation expense	1.3		2.6	1.4
Performances Shares [Member]	'		'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'
Unrecognized compensation expense	4		'	'
Intrinsic Value Performance Shares Vested	2.2		0	3.3
Minimum percentage of performance shares issued	0.00%		'	'
Maximum percentage of performance shares issued	200.00%		'	'
Shares granted during the period	109,076	[1]	'	'
Weighted-average grant date fair value, vested	$41.14		'	'
Fair value of shares expected to vest	11.6		'	'
Performance Units [Member]	'		'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'
Unrecognized compensation expense	2.5		'	'
Value of performance units vested	$1		'	'
Fair value of units expected to vest	4.9		'	'
Cash To Settle Performance Unit Awards	2		0	2.8
Shares granted during the period	4,658,648		'	'
Liability for Equity Option Awards Outstanding	2.4		4.9	2.1
Stock Option [Member]	'		'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'
Cash received from stock options exercised	0.7		0	0.8
Tax benefit realized from exercised stock options	0.1		0	0.1
Omnibus Plan [Member]	'		'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'
Shares authorized for issue under plan	1,700,000		'	'
Directors Stock Compensation Plan [Member]	'		'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'
Shares authorized for issue under plan	270,000		'	'
Compensation expense recognized	0.7		0.7	0.5
Tax benefit from compensation expense	$0.30		$0.30	$0.20
Shares granted during the period	17,000		16,600	11,900
Weighted-average grant date fair value, vested	$40.06		$40.46	$44.30
[1]	The number of common shares issued related to performance shares may range from zero to 200B percent of the number of shares shown in the table above based on our achievement of performance goals for total shareholder return relative to a selected peer group of companies.

Stock_Based_Compensation_Table1

Stock Based Compensation (Table 1) (Details) (USD $)	12 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
Performances Shares [Member]	'		'		'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]	'		'		'
Non-vested and outstanding, beginning of year	295,973	[1]	'		'
Granted	109,076	[1]	'		'
Vested	-84,849	[1]	'		'
Cancelled/Forfeited	-18,822	[1]	'		'
Non-vested and outstanding, end of year	301,378	[1]	295,973	[1]	'
Weighted-average grant date fair value, non-vested and outstanding, beginning of year	$39.88		'		'
Weighted-average grant date fair value, granted	$42.88		$39.73		$38.99
Weighted-average grant date fair value, vested	$41.14		'		'
Weighted-average grant date fair value, cancelled/forfeited	$40.47		'		'
Weighted-average grant date fair value, non-vested and outstanding, end of year	$40.57		$39.88		'
Performance Units [Member]	'		'		'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]	'		'		'
Non-vested and outstanding, beginning of year	11,582,556		'		'
Granted	4,658,648		'		'
Vested	-3,205,636		'		'
Cancelled/Forfeited	-766,647		'		'
Non-vested and outstanding, end of year	12,268,921		'		'
[1]	The number of common shares issued related to performance shares may range from zero to 200B percent of the number of shares shown in the table above based on our achievement of performance goals for total shareholder return relative to a selected peer group of companies.

Stock_Based_Compensation_Table2

Stock Based Compensation (Table 2) (Details) (USD $)	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Performances Shares [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]	'	'	'
Expected stock-price volatility	19.10%	19.40%	27.80%
Dividend yield	3.93%	3.98%	3.97%
Weighted-average grant date fair value, granted	$42.88	$39.73	$38.99
Performance Units [Member] | Grant 2012 [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]	'	'	'
Expected stock-price volatility	19.50%	'	'
Performance Units [Member] | Grant 2013 [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]	'	'	'
Expected stock-price volatility	18.10%	'	'

Stock_Based_Compensation_Table3

Stock Based Compensation (Table 3) (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Stock options outstanding, beginning	26,372	'
Stock options granted	0	'
Stock options exercised	-21,054	'
Stock options exercisable	5,318	'
Stock options cancelled/forfeited	0	'
Stock options outstanding, end of year	5,318	26,372
Weighted-average exercise price, outstanding	$31.34	$31.34
Weighted-average exercise price, granted	$0	'
Weighted-average exercise price, exercised	$31.34	'
Weighted-average exercise price, cancelled/forfeited	$0	'
Weighted-average exercise price, exercisable	$31.34	'
Weighted-average remaining contractual term, outstanding	'2 years	'4 years 0 months
Weighted-average remaining contractual term, exercisable	'2 years	'
Aggregate intrinsic value, outstanding	$57	$235
Aggregate intrinsic value, exercisable	57	'
Weighted Average Contractual Term - Granted	'0 years	'
Weighted Average Contractual Term - Excercised	'0 years	'
Weighted Average Contractual Term - Cancelled	'0 years	'
Aggregate Intrinsic Value - Granted	0	'
Aggregate Intrinsic Value - Exercised	232	'
Aggregate Intrinsic Value - Cancelled	$0	'

Environmental_Matter_Narrative

Environmental Matter (Narrative) (Details) (Washington Gas Light Company)	12 Months Ended
	Sep. 30, 2014
Number of Sites	10
Accrual For Environmental Costs	'
Number of Sites	4
District of Columbia	'
Recovery of environmental response costs	'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
Maryland	'
Recovery of environmental response costs	'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
Virginia	'
Recovery of environmental response costs	'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

Environmentat_Matters_Narrativ

Environmentat Matters (Narrative) (Details) (Washington Gas Light Company, USD $)	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Schedule of Regulatory Assets and Liabilities [Line Items]	'	'
Regulatory Assets, Noncurrent	$71,584,000	$65,984,000
Environmental Exit Costs, Reasonably Possible Additional Losses, High Estimate	19,300,000	20,500,000
Accrual For Environmental Costs	'	'
Schedule of Regulatory Assets and Liabilities [Line Items]	'	'
Accrual for Environmental Loss Contingencies	8,500,000	8,500,000
Environmental response costs	'	'
Schedule of Regulatory Assets and Liabilities [Line Items]	'	'
Regulatory Assets, Noncurrent	$600,000	$600,000

Commitments_and_Contingencies_

Commitments and Contingencies (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013	Sep. 30, 2012
	Counterparties
Commitments and Contingencies [Line Items]	'		'	'
Operating Leases, Rent Expense	$5.50		$5.60	$5.20
Construction Project Financing	8.3		6.7	'
Number Of Service Agreements With Pipeline Companies	4		'	'
Reserve for Bad Debt-Construction Project Financing	0		0	'
WGL Holdings, Inc.	'		'	'
Commitments and Contingencies [Line Items]	'		'	'
Recorded Unconditional Purchase Obligation	528.5		'	'
WGESystems	'		'	'
Commitments and Contingencies [Line Items]	'		'	'
Recorded Unconditional Purchase Obligation	6		'	'
Accrual for Loss Contingency	2.6		'	'
Other External Partners	'		'	'
Commitments and Contingencies [Line Items]	'		'	'
Recorded Unconditional Purchase Obligation	18.7		'	'
Maximum [Member]	'		'	'
Commitments and Contingencies [Line Items]	'		'	'
Pipeline Service Agreements Expiration Dates Range	'2032		'	'
Other Agreements And Peaking Services Expiration Dates Range	'2032		'	'
Maximum [Member] | WGEServices	'		'	'
Commitments and Contingencies [Line Items]	'		'	'
Asset Optimization Pipeline Transportation Storage And Peaking Contracts Range	'2025	[1]	'	'
Maximum [Member] | WGL Midstream	'		'	'
Commitments and Contingencies [Line Items]	'		'	'
Asset Optimization Pipeline Transportation Storage And Peaking Contracts Range	'2044	[2]	'	'
Minimum [Member]	'		'	'
Commitments and Contingencies [Line Items]	'		'	'
Pipeline Service Agreements Expiration Dates Range	'2015		'	'
Other Agreements And Peaking Services Expiration Dates Range	'2015		'	'
Asset Optimization Pipeline Transportation Storage And Peaking Contracts Range	'2015		'	'
Retail Energy Marketing [Member]	'		'	'
Commitments and Contingencies [Line Items]	'		'	'
Recorded Unconditional Purchase Obligation	227.3		'	'
Subsidiary of Common Parent [Member] | WGL Midstream	'		'	'
Commitments and Contingencies [Line Items]	'		'	'
Recorded Unconditional Purchase Obligation	$276.50		'	'
[1]	Represents minimum payments for natural gas transportation, storage and peaking contracts that have expiration dates through fiscal year 2025.
[2]	Represents minimum payments for natural gas transportation, storage and peaking contracts that have expiration dates through fiscal year 2044.

Committments_and_Contingencies1

Committments and Contingencies - Tables (Details) (USD $)	Sep. 30, 2014
Minimum Payments Under Operating Leases [Abstract]	'
Operating Leases, Future Minimum Payments Due, Current	$7,800,000
Operating Leases, Future Minimum Payments, Due in Two Years	6,300,000
Operating Leases, Future Minimum Payments, Due in Three Years	4,900,000
Operating Leases, Future Minimum Payments, Due in Four Years	4,300,000
Operating Leases, Future Minimum Payments, Due in Five Years	1,000,000
Operating Leases, Future Minimum Payments, Due Thereafter	10,500,000
Operating Leases, Future Minimum Payments Due	34,800,000
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	573,800,000
Unrecorded Unconditional Purchase Obligation, Due within Two Years	265,300,000
Unrecorded Unconditional Purchase Obligation, Due within Three Years	177,300,000
Unrecorded Unconditional Purchase Obligation, Due within Four Years	937,300,000
Unrecorded Unconditional Purchase Obligation, Due within Five Years	958,600,000
Unrecorded Unconditional Purchase Obligation, Due after Five Years	13,742,000,000
Unrecorded Unconditional Purchase Obligation	16,654,300,000
Gas Purchase Committments [Member]	'
Footnote Details [Abstract]	'
Commitments Related To Renewable Energy Credits	15,300,000	[1]
Gas Purchase Committments [Member] | Washington Gas Light Company	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	280,000,000	[2]
Unrecorded Unconditional Purchase Obligation, Due within Two Years	288,900,000	[2]
Unrecorded Unconditional Purchase Obligation, Due within Three Years	336,700,000	[2]
Unrecorded Unconditional Purchase Obligation, Due within Four Years	323,200,000	[2]
Unrecorded Unconditional Purchase Obligation, Due within Five Years	303,500,000	[2]
Unrecorded Unconditional Purchase Obligation, Due after Five Years	2,990,200,000	[2]
Unrecorded Unconditional Purchase Obligation	4,522,500,000	[2]
Gas Purchase Committments [Member] | Retail Energy Marketing [Member]	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	167,500,000	[3]
Unrecorded Unconditional Purchase Obligation, Due within Two Years	49,200,000	[3]
Unrecorded Unconditional Purchase Obligation, Due within Three Years	13,800,000	[3]
Unrecorded Unconditional Purchase Obligation, Due within Four Years	600,000	[3]
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0	[3]
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0	[3]
Unrecorded Unconditional Purchase Obligation	231,100,000	[3]
Gas Purchase Committments [Member] | WGL Midstream	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	29,200,000	[4]
Unrecorded Unconditional Purchase Obligation, Due within Two Years	24,400,000	[4]
Unrecorded Unconditional Purchase Obligation, Due within Three Years	80,200,000	[4]
Unrecorded Unconditional Purchase Obligation, Due within Four Years	906,000,000	[4]
Unrecorded Unconditional Purchase Obligation, Due within Five Years	933,400,000	[4]
Unrecorded Unconditional Purchase Obligation, Due after Five Years	13,479,800,000	[4]
Unrecorded Unconditional Purchase Obligation	15,453,000,000	[4]
Electric Purchase Committments [Member] | Retail Energy Marketing [Member]	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	359,400,000	[1]
Unrecorded Unconditional Purchase Obligation, Due within Two Years	171,700,000	[1]
Unrecorded Unconditional Purchase Obligation, Due within Three Years	65,000,000	[1]
Unrecorded Unconditional Purchase Obligation, Due within Four Years	3,600,000	[1]
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0	[1]
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0	[1]
Unrecorded Unconditional Purchase Obligation	599,700,000	[1]
Pipeline Contracts [Member] | Washington Gas Light Company	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	195,400,000	[5]
Unrecorded Unconditional Purchase Obligation, Due within Two Years	224,700,000	[5]
Unrecorded Unconditional Purchase Obligation, Due within Three Years	217,700,000	[5]
Unrecorded Unconditional Purchase Obligation, Due within Four Years	211,100,000	[5]
Unrecorded Unconditional Purchase Obligation, Due within Five Years	201,300,000	[5]
Unrecorded Unconditional Purchase Obligation, Due after Five Years	1,205,300,000	[5]
Unrecorded Unconditional Purchase Obligation	2,255,500,000	[5]
Pipeline Contracts [Member] | Retail Energy Marketing [Member]	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	2,400,000	[6]
Unrecorded Unconditional Purchase Obligation, Due within Two Years	600,000	[6]
Unrecorded Unconditional Purchase Obligation, Due within Three Years	600,000	[6]
Unrecorded Unconditional Purchase Obligation, Due within Four Years	600,000	[6]
Unrecorded Unconditional Purchase Obligation, Due within Five Years	600,000	[6]
Unrecorded Unconditional Purchase Obligation, Due after Five Years	1,300,000	[6]
Unrecorded Unconditional Purchase Obligation	6,100,000	[6]
Pipeline Contracts [Member] | WGL Midstream	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	15,300,000	[7]
Unrecorded Unconditional Purchase Obligation, Due within Two Years	19,400,000	[7]
Unrecorded Unconditional Purchase Obligation, Due within Three Years	17,700,000	[7]
Unrecorded Unconditional Purchase Obligation, Due within Four Years	26,500,000	[7]
Unrecorded Unconditional Purchase Obligation, Due within Five Years	24,600,000	[7]
Unrecorded Unconditional Purchase Obligation, Due after Five Years	260,900,000	[7]
Unrecorded Unconditional Purchase Obligation	$364,400,000	[7]
[1]	Represents electric purchase commitments that are based on existing fixed price and fixed volume contracts. Includes $15.3 million of commitments related to renewable energy credits.
[2]	(b) The contracts referenced above are estimated based on market prices at September 30, 2014.
[3]	Represents fixed price commitments with city gate equivalent deliveries.
[4]	Includes short-term commitments to purchase fixed volumes of natural gas, as well as long-term gas purchase commitments that contain fixed volume purchase requirements. Cost estimates are based on forward market prices for purchases under these purchase commitments.
[5]	(a) Represents minimum payments for natural gas transportation, storage and peaking contracts that have expiration dates through fiscal year 2032.
[6]	Represents minimum payments for natural gas transportation, storage and peaking contracts that have expiration dates through fiscal year 2025.
[7]	Represents minimum payments for natural gas transportation, storage and peaking contracts that have expiration dates through fiscal year 2044.

Derivative_and_Weather_Related2

Derivative and Weather Related Instruments (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
Asset Optimization [Abstract]	'		'		'
Gain (Loss) on Asset Optimization Transactions Net Pretax	($35.40)		($33.20)		$28.30
Unrealized Gains (Loss) On Asset Optimization Derivative Instruments Net Pretax	-66.2		-45.4		15.9
Interest Rate Derivatives [Abstract]	'		'		'
Discussion Of Interest Rate Derivative Risk Management Policy	'WGL utilizes derivative instruments that are designed to minimize the risk of interest-rate volatility associated with future debt issuances. During September 2014, WGL entered into interest rate swaps associated with an expected $150 million debt issuance. WGL elected cash flow hedge accounting for its interest rate derivative instruments.		'		'
Ineffective portion of cash flow hedge-net	0.2		'		'
WGEServices	'		'		'
Derivative, Collateral [Abstract]	'		'		'
Right to Reclaim Cash	5.7		12.1		'
Collateral Already Posted Aggregate Fair Value	5.3		3.6		'
WGL Midstream	'		'		'
Derivative, Collateral [Abstract]	'		'		'
Right to Reclaim Cash	11.4		8.1		'
WGL Holdings, Inc.	'		'		'
Absolute Notional Amounts of Open Positions on Derivative Instruments	'		'		'
Interest Rate Swap Notional Principal Value	150		75	[1]	'
Warrant Transaction Volume of Shares	4.6		4.6		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Netting of Collateral	12		0.9		'
Total	-306.3	[2]	-126.6	[2]	'
WGL Holdings, Inc. | Derivative Instruments Designated as Hedging Instruments	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	0		0		'
Gross Derivative Liabilities	-1.7		0		'
WGL Holdings, Inc. | Derivative Instruments Not Designated as Hedging Instruments	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	72.6		120.3		'
Gross Derivative Liabilities	-389.2		-247.8		'
WGL Holdings, Inc. | Current assets- derivatives	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Netting of Collateral	0		-2.7		'
Total	18.3	[2]	35.3	[2]	'
WGL Holdings, Inc. | Current assets- derivatives | Derivative Instruments Designated as Hedging Instruments	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	0		0		'
Gross Derivative Liabilities	0		0		'
WGL Holdings, Inc. | Current assets- derivatives | Derivative Instruments Not Designated as Hedging Instruments	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	20.8		57.3		'
Gross Derivative Liabilities	-2.5		-19.3		'
WGL Holdings, Inc. | Non current assets- derivatives	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Netting of Collateral	0		0		'
Total	18.7	[2]	26.3	[2]	'
WGL Holdings, Inc. | Non current assets- derivatives | Derivative Instruments Designated as Hedging Instruments	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	0		0		'
Gross Derivative Liabilities	0		0		'
WGL Holdings, Inc. | Non current assets- derivatives | Derivative Instruments Not Designated as Hedging Instruments	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	18.7		57.4		'
Gross Derivative Liabilities	0		-31.1		'
WGL Holdings, Inc. | Accounts Payable And OtherAccrued Liabilities [Member]	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Netting of Collateral	0		0		'
Total	0	[2]	1.5	[2]	'
WGL Holdings, Inc. | Accounts Payable And OtherAccrued Liabilities [Member] | Derivative Instruments Designated as Hedging Instruments	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	0		0		'
Gross Derivative Liabilities	0		0		'
WGL Holdings, Inc. | Accounts Payable And OtherAccrued Liabilities [Member] | Derivative Instruments Not Designated as Hedging Instruments	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	0		1.5		'
Gross Derivative Liabilities	0		0		'
WGL Holdings, Inc. | Current liabilities- Derivatives	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Netting of Collateral	8		0.9		'
Total	-48.6	[2]	-48.4	[2]	'
WGL Holdings, Inc. | Current liabilities- Derivatives | Derivative Instruments Designated as Hedging Instruments	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	0		0		'
Gross Derivative Liabilities	-1.7		0		'
WGL Holdings, Inc. | Current liabilities- Derivatives | Derivative Instruments Not Designated as Hedging Instruments	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	15.4		4.1		'
Gross Derivative Liabilities	-70.3		-53.4		'
WGL Holdings, Inc. | Non current liabilities- derivatives	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Netting of Collateral	4		2.7		'
Total	-294.7	[2]	-141.3	[2]	'
WGL Holdings, Inc. | Non current liabilities- derivatives | Derivative Instruments Designated as Hedging Instruments	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	0		0		'
Gross Derivative Liabilities	0		0		'
WGL Holdings, Inc. | Non current liabilities- derivatives | Derivative Instruments Not Designated as Hedging Instruments	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	17.7		0		'
Gross Derivative Liabilities	-316.4		-144		'
WGL Holdings, Inc. | Asset Optimization [Member]	'		'		'
Absolute Notional Amounts of Open Positions on Derivative Instruments	'		'		'
Natural Gas Derivative Transaction, Volume	20,593,300,000		13,289,600,000		'
WGL Holdings, Inc. | Retail Sales [Member]	'		'		'
Absolute Notional Amounts of Open Positions on Derivative Instruments	'		'		'
Natural Gas Derivative Transaction, Volume	44,700,000		98,900,000		'
Electricity Derivative Transaction, Volume	3,831,400,000		4,790,200,000		'
WGL Holdings, Inc. | Other Risk Management Activities [Member]	'		'		'
Absolute Notional Amounts of Open Positions on Derivative Instruments	'		'		'
Natural Gas Derivative Transaction, Volume	1,641,300,000		1,803,600,000		'
Electricity Derivative Transaction, Volume	16,734,100,000		17,647,900,000		'
Washington Gas Light Company	'		'		'
Derivative, Collateral [Abstract]	'		'		'
Right to Reclaim Cash	8.2		3		'
Derivative, Collateral, Obligation to Return Cash	2.5		4.6		'
Absolute Notional Amounts of Open Positions on Derivative Instruments	'		'		'
Interest Rate Swap Notional Principal Value	0		75	[1]	'
Warrant Transaction Volume of Shares	0		0		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	26.2	[3]	68	[3]	'
Gross Derivative Liabilities	-308.4	[3]	-175.7	[3]	'
Netting of Collateral	0.9	[3]	-2.7	[3]	'
Total	-281.3	[2],[3]	-110.4	[2],[3]	'
Washington Gas Light Company | Current assets- derivatives	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	3.9	[3]	19.3	[3]	'
Gross Derivative Liabilities	0	[3]	-12.3	[3]	'
Netting of Collateral	0	[3]	-2.7	[3]	'
Total	3.9	[2],[3]	4.3	[2],[3]	'
Washington Gas Light Company | Non current assets- derivatives	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	9.5	[3]	47.2	[3]	'
Gross Derivative Liabilities	0	[3]	-31.1	[3]	'
Netting of Collateral	0	[3]	0	[3]	'
Total	9.5	[2],[3]	16.1	[2],[3]	'
Washington Gas Light Company | Current liabilities- Derivatives	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	8.6	[3]	1.5	[3]	'
Gross Derivative Liabilities	-43.2	[3]	-26.2	[3]	'
Netting of Collateral	0.7	[3]	0	[3]	'
Total	-33.9	[2],[3]	-24.7	[2],[3]	'
Washington Gas Light Company | Non current liabilities- derivatives	'		'		'
Balance Sheet Classification of Derivative Instruments	'		'		'
Gross Derivative Assets	4.2	[3]	0	[3]	'
Gross Derivative Liabilities	-265.2	[3]	-106.1	[3]	'
Netting of Collateral	0.2	[3]	0	[3]	'
Total	($260.80)	[2],[3]	($106.10)	[2],[3]	'
Washington Gas Light Company | Asset Optimization [Member]	'		'		'
Absolute Notional Amounts of Open Positions on Derivative Instruments	'		'		'
Natural Gas Derivative Transaction, Volume	13,740,900,000		11,115,800,000		'
Washington Gas Light Company | Retail Sales [Member]	'		'		'
Absolute Notional Amounts of Open Positions on Derivative Instruments	'		'		'
Natural Gas Derivative Transaction, Volume	0		0		'
Electricity Derivative Transaction, Volume	0		0		'
Washington Gas Light Company | Other Risk Management Activities [Member]	'		'		'
Absolute Notional Amounts of Open Positions on Derivative Instruments	'		'		'
Natural Gas Derivative Transaction, Volume	1,398,200,000		1,455,700,000		'
Electricity Derivative Transaction, Volume	0		0		'
[1]	The fair value of our interest rate swaps was minimal at September 30, 2013.
[2]	WGL 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 815. All recognized derivative contracts and associated financial collateral subject to a master netting arrangement or similar that is eligible for offset under ASC 815 have been presented net in the balance sheet.
[3]	Washington Gas did not have any derivative instruments outstanding that were designated as hedging instruments at September 30, 2014, or 2013.

Derivative_and_Weather_Related3

Derivative and Weather Related Instruments (Gains and Losses) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
WGL Holdings, Inc.	'		'		'
Gains and (Losses) on Derivative Instruments	'		'		'
Recorded to other comprehensive income	($1.50)	[1]	$0	[1]	$0	[1]
Gains (Losses) On Derivative Instruments	-244.9		-173.1		50.4
Potential Collateral Requirements for Derivative Liabilities with Credit-risk-Contingent Features	'		'		'
Derivative liabilities with credit-risk-contingent features	28.8		77		'
Maximum potential collateral requirements	16.5		33.6		'
WGL Holdings, Inc. | Operating Revenues Non Utility [Member]	'		'		'
Gains and (Losses) on Derivative Instruments	'		'		'
Recorded to income	-47.9		-9.9		19.2
WGL Holdings, Inc. | Utility Cost Of Gas [Member]	'		'		'
Gains and (Losses) on Derivative Instruments	'		'		'
Recorded to income	-87.3		-45.9		22.3
WGL Holdings, Inc. | Non Utility Cost Of Energy Related Sales [Member]	'		'		'
Gains and (Losses) on Derivative Instruments	'		'		'
Recorded to income	36.2		-2.4		-34.2
WGL Holdings, Inc. | Other Income [Member]	'		'		'
Gains and (Losses) on Derivative Instruments	'		'		'
Other income net	-1.1		0.2		0.9
WGL Holdings, Inc. | Gas Costs [Member]	'		'		'
Gains and (Losses) on Derivative Instruments	'		'		'
Recorded to regulatory assets/liabilities	-143.3		-115.1		42.2
WGL Holdings, Inc. | Other Regulatory Assets Liability [Member]	'		'		'
Gains and (Losses) on Derivative Instruments	'		'		'
Recorded to regulatory assets/liabilities	0.2		0		0
WGL Holdings, Inc. | Interest expense [Member]	'		'		'
Gains and (Losses) on Derivative Instruments	'		'		'
Recorded to income	-0.2		0		0
Washington Gas Light Company	'		'		'
Gains and (Losses) on Derivative Instruments	'		'		'
Gains (Losses) On Derivative Instruments	-230.4		-161		64.5
Potential Collateral Requirements for Derivative Liabilities with Credit-risk-Contingent Features	'		'		'
Derivative liabilities with credit-risk-contingent features	20.6		44.7		'
Maximum potential collateral requirements	16.1		1.7		'
Washington Gas Light Company | Utility Cost Of Gas [Member]	'		'		'
Gains and (Losses) on Derivative Instruments	'		'		'
Recorded to income	-87.3		-45.9		22.3
Washington Gas Light Company | Gas Costs [Member]	'		'		'
Gains and (Losses) on Derivative Instruments	'		'		'
Recorded to regulatory assets/liabilities	-143.3		-115.1		42.2
Washington Gas Light Company | Other Regulatory Assets Liability [Member]	'		'		'
Gains and (Losses) on Derivative Instruments	'		'		'
Recorded to regulatory assets/liabilities	$0.20		$0		$0
[1]	This pre-tax unrealized gain represents the effective portion of our cash flow hedge. Upon settlement of the hedge, the realized gain or loss, to the extent effective, will be amortized as an adjustment to the interest expense. We expect this amortization to be minimal for fiscal 2015.

Derivative_and_Weather_Related4

Derivative and Weather Related Instruments (Details 2) (USD $)	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
In Millions, unless otherwise specified
WGEServices	'	'	'
Concentration of Credit Risk	'	'	'
Obligation to counterparties	$4.10	'	'
Percentage Of Credit Exposure	10.00%	'	'
Number of Counterparties	2	'	'
WGEServices | Weather Instruments [Member]	'	'	'
Gain (Loss) On Derivative Instruments Net Pretax [Abstract]	'	'	'
Gain (losses) on weather related instruments, pretax	3.4	-0.8	11.8
WGL Midstream	'	'	'
Concentration of Credit Risk	'	'	'
Obligation to counterparties	13.6	'	'
Percentage Of Credit Exposure	10.00%	'	'
Number of Counterparties	3	'	'
Washington Gas Light Company	'	'	'
Concentration of Credit Risk	'	'	'
Obligation to counterparties	16.7	'	'
Percentage Of Credit Exposure	10.00%	'	'
Number of Counterparties	3	'	'
Washington Gas Light Company | Weather Instruments [Member]	'	'	'
Gain (Loss) On Derivative Instruments Net Pretax [Abstract]	'	'	'
Gain (losses) on weather related instruments, pretax	'	$0.80	$7.90

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	Sep. 30, 2014	Sep. 30, 2013
In Millions, unless otherwise specified
WGL Holdings, Inc.	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	$72.60	$120.30
Liabilities	-390.9	-247.8
WGL Holdings, Inc. | Natural Gas Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	56.4	93.8
Liabilities	-368.2	-217.8
WGL Holdings, Inc. | Electricity Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	16.2	25.4
Liabilities	-21	-30
WGL Holdings, Inc. | Interest Rate Derivative	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
Liabilities	-1.7	0
WGL Holdings, Inc. | Warrant	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	1.1
Liabilities	0	0
WGL Holdings, Inc. | Level 1 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
Liabilities	0	0
WGL Holdings, Inc. | Level 1 [Member] | Natural Gas Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
Liabilities	0	0
WGL Holdings, Inc. | Level 1 [Member] | Electricity Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
Liabilities	0	0
WGL Holdings, Inc. | Level 1 [Member] | Interest Rate Derivative	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
Liabilities	0	0
WGL Holdings, Inc. | Level 1 [Member] | Warrant	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
Liabilities	0	0
WGL Holdings, Inc. | Level 2 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	23	72.3
Liabilities	-41.6	-48.1
WGL Holdings, Inc. | Level 2 [Member] | Natural Gas Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	22.7	72.3
Liabilities	-39.8	-41.1
WGL Holdings, Inc. | Level 2 [Member] | Electricity Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0.3	0
Liabilities	-0.1	-7
WGL Holdings, Inc. | Level 2 [Member] | Interest Rate Derivative	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
Liabilities	-1.7	0
WGL Holdings, Inc. | Level 2 [Member] | Warrant	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
Liabilities	0	0
WGL Holdings, Inc. | Level 3 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	49.6	48
Liabilities	-349.3	-199.7
WGL Holdings, Inc. | Level 3 [Member] | Natural Gas Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	33.7	21.5
Liabilities	-328.4	-176.7
WGL Holdings, Inc. | Level 3 [Member] | Electricity Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	15.9	25.4
Liabilities	-20.9	-23
WGL Holdings, Inc. | Level 3 [Member] | Interest Rate Derivative	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
Liabilities	0	0
WGL Holdings, Inc. | Level 3 [Member] | Warrant	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	1.1
Liabilities	0	0
Washington Gas Light Company	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	26.2	68
Liabilities	-308.4	-175.7
Washington Gas Light Company | Natural Gas Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	26.2	68
Liabilities	-308.4	-175.7
Washington Gas Light Company | Level 1 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
Liabilities	0	0
Washington Gas Light Company | Level 1 [Member] | Natural Gas Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
Liabilities	0	0
Washington Gas Light Company | Level 2 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	13.5	51
Liabilities	-25.1	-25.1
Washington Gas Light Company | Level 2 [Member] | Natural Gas Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	13.5	51
Liabilities	-25.1	-25.1
Washington Gas Light Company | Level 3 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	12.7	17
Liabilities	-283.3	-150.6
Washington Gas Light Company | Level 3 [Member] | Natural Gas Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	12.7	17
Liabilities	($283.30)	($150.60)

Fair_Value_Measurements_Reconc

Fair Value Measurements (Reconciliation with Level 3 Inputs) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
WGL Holdings, Inc.	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	($151.70)	$42.80	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	-79.4	-94.8	-16.8
Recorded to regulatory assets-gas costs	-113.6	-115.3	'
Transfers out of Level 3	1.7	-18.1	'
Purchases	5.2	5.7	'
Settlements	38.1	28	'
Balance at end of period	-299.7	-151.7	42.8
WGL Holdings, Inc. | Weather Instruments [Member]	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	0	-0.5	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	0	1.2	7.9
Recorded to regulatory assets-gas costs	0	0	'
Transfers out of Level 3	0	-0.7	'
Purchases	0	0	'
Settlements	0	0	'
Balance at end of period	0	0	-0.5
WGL Holdings, Inc. | Natural Gas Related Derivatives [Member]	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	-155.2	39.6	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	-72.6	-72.4	22.1
Recorded to regulatory assets-gas costs	-113.6	-115.3	'
Transfers out of Level 3	1.7	-17.4	'
Purchases	0	0	'
Settlements	45	10.3	'
Balance at end of period	-294.7	-155.2	39.6
WGL Holdings, Inc. | Electricity Related Derivatives [Member]	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	2.4	2.8	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	-5.7	-23.8	-47.7
Recorded to regulatory assets-gas costs	0	0	'
Transfers out of Level 3	0	0	'
Purchases	5.2	5.7	'
Settlements	-6.9	17.7	'
Balance at end of period	-5	2.4	2.8
WGL Holdings, Inc. | Warrant	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	1.1	0.9	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	-1.1	0.2	0.9
Recorded to regulatory assets-gas costs	0	0	'
Transfers out of Level 3	0	0	'
Purchases	0	0	'
Settlements	0	0	'
Balance at end of period	0	1.1	0.9
Washington Gas Light Company	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	-133.6	35.1	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	-69.4	-44.7	22.2
Recorded to regulatory assets-gas costs	-113.6	-115.3	'
Transfers out of Level 3	1.7	-18.1	'
Settlements	44.3	9.4	'
Balance at end of period	-270.6	-133.6	35.1
Washington Gas Light Company | Weather Instruments [Member]	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	0	-0.5	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	0	1.2	7.9
Recorded to regulatory assets-gas costs	0	0	'
Transfers out of Level 3	0	-0.7	'
Settlements	0	0	'
Balance at end of period	0	0	-0.5
Washington Gas Light Company | Natural Gas Related Derivatives [Member]	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	-133.6	35.6	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	-69.4	-45.9	14.3
Recorded to regulatory assets-gas costs	-113.6	-115.3	'
Transfers out of Level 3	1.7	-17.4	'
Settlements	44.3	9.4	'
Balance at end of period	-270.6	-133.6	35.6
Washington Gas Light Company | Electricity Related Derivatives [Member]	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	0	0	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	0	0	0
Recorded to regulatory assets-gas costs	0	0	'
Transfers out of Level 3	0	0	'
Settlements	0	0	'
Balance at end of period	0	0	0
Washington Gas Light Company | Warrant	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	0	0	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	0	0	0
Recorded to regulatory assets-gas costs	0	0	'
Transfers out of Level 3	0	0	'
Settlements	0	0	'
Balance at end of period	$0	$0	$0

Fair_Value_Measurements_Realiz

Fair Value Measurements (Realized and Unrealized Gains and Losses with Level 3 Measurements) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
WGL Holdings, Inc.	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	($79.40)	($94.80)	($16.80)
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	-109.9	-111.6	23.2
Total Unrealized Gains (Losses)	-176.7	-175.3	62
WGL Holdings, Inc. | Natural Gas Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-72.6	-72.4	22.1
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	-109.9	-111.6	23.2
Total Unrealized Gains (Losses)	-171.8	-181	42.1
WGL Holdings, Inc. | Electricity Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-5.7	-23.8	-47.7
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	0	0	0
Total Unrealized Gains (Losses)	-3.8	5.5	18.8
WGL Holdings, Inc. | Weather Instruments [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	1.2	7.9
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	0	0	0
Total Unrealized Gains (Losses)	0	0	0.2
WGL Holdings, Inc. | Warrant	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-1.1	0.2	0.9
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	0	0	0
Total Unrealized Gains (Losses)	-1.1	0.2	0.9
WGL Holdings, Inc. | Operating Revenues Non Utility [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-24.4	-36.1	-11.2
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-38.8	-18.7	9.1
WGL Holdings, Inc. | Operating Revenues Non Utility [Member] | Natural Gas Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-2.3	-27	3
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-5	-25.3	4.3
WGL Holdings, Inc. | Operating Revenues Non Utility [Member] | Electricity Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-22.1	-9.1	-14.2
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-33.8	6.6	4.8
WGL Holdings, Inc. | Operating Revenues Non Utility [Member] | Weather Instruments [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
WGL Holdings, Inc. | Operating Revenues Non Utility [Member] | Warrant	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
WGL Holdings, Inc. | Utility Cost Of Gas [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-69.4	-45.8	14.3
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-60.6	-44.3	13.8
WGL Holdings, Inc. | Utility Cost Of Gas [Member] | Natural Gas Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-69.4	-45.8	14.3
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-60.6	-44.3	13.8
WGL Holdings, Inc. | Utility Cost Of Gas [Member] | Electricity Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
WGL Holdings, Inc. | Utility Cost Of Gas [Member] | Weather Instruments [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
WGL Holdings, Inc. | Utility Cost Of Gas [Member] | Warrant	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
WGL Holdings, Inc. | OtherIncomeMember	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-1.1	0.2	0.9
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-1.1	0.2	0.9
WGL Holdings, Inc. | OtherIncomeMember | Natural Gas Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
WGL Holdings, Inc. | OtherIncomeMember | Electricity Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
WGL Holdings, Inc. | OtherIncomeMember | Weather Instruments [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
WGL Holdings, Inc. | OtherIncomeMember | Warrant	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-1.1	0.2	0.9
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-1.1	0.2	0.9
WGL Holdings, Inc. | Non Utility Cost Of Energy Related Sales [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	15.5	-14.3	-28.7
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	33.7	-0.9	14.8
WGL Holdings, Inc. | Non Utility Cost Of Energy Related Sales [Member] | Natural Gas Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-0.9	0.4	4.8
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	3.7	0.2	0.8
WGL Holdings, Inc. | Non Utility Cost Of Energy Related Sales [Member] | Electricity Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	16.4	-14.7	-33.5
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	30	-1.1	14
WGL Holdings, Inc. | Non Utility Cost Of Energy Related Sales [Member] | Weather Instruments [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
WGL Holdings, Inc. | Non Utility Cost Of Energy Related Sales [Member] | Warrant	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
WGL Holdings, Inc. | Operation And Maintenance Expense [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	1.2	7.9
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0.2
WGL Holdings, Inc. | Operation And Maintenance Expense [Member] | Natural Gas Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
WGL Holdings, Inc. | Operation And Maintenance Expense [Member] | Electricity Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
WGL Holdings, Inc. | Operation And Maintenance Expense [Member] | Weather Instruments [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	1.2	7.9
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0.2
WGL Holdings, Inc. | Operation And Maintenance Expense [Member] | Warrant	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Washington Gas Light Company	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-69.4	-44.7	22.2
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	-109.9	-111.6	23.2
Total Unrealized Gains (Losses)	-170.5	-155.9	37.2
Washington Gas Light Company | Natural Gas Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-69.4	-45.9	14.3
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	-109.9	-111.6	23.2
Total Unrealized Gains (Losses)	-170.5	-155.9	37
Washington Gas Light Company | Electricity Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	0	0	0
Total Unrealized Gains (Losses)	0	0	0
Washington Gas Light Company | Weather Instruments [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	1.2	7.9
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	0	0	0
Total Unrealized Gains (Losses)	0	0	0.2
Washington Gas Light Company | Warrant	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	0	0	0
Total Unrealized Gains (Losses)	0	0	0
Washington Gas Light Company | Utility Cost Of Gas [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-69.4	-45.9	14.3
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-60.6	-44.3	13.8
Washington Gas Light Company | Utility Cost Of Gas [Member] | Natural Gas Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-69.4	-45.9	14.3
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-60.6	-44.3	13.8
Washington Gas Light Company | Utility Cost Of Gas [Member] | Electricity Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Washington Gas Light Company | Utility Cost Of Gas [Member] | Weather Instruments [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Washington Gas Light Company | Utility Cost Of Gas [Member] | Warrant	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Washington Gas Light Company | Operation And Maintenance Expense [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	1.2	7.9
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0.2
Washington Gas Light Company | Operation And Maintenance Expense [Member] | Natural Gas Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Washington Gas Light Company | Operation And Maintenance Expense [Member] | Electricity Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Washington Gas Light Company | Operation And Maintenance Expense [Member] | Weather Instruments [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	1.2	7.9
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	0.2
Washington Gas Light Company | Operation And Maintenance Expense [Member] | Warrant	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0	0	0
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	$0	$0	$0

Fair_Value_Measurements_Fair_V

Fair Value Measurements (Fair Value of Financial Instruments) (Details) (USD $)	Sep. 30, 2014		Sep. 30, 2013
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'		'
Commercial Paper	$453,500,000		$373,100,000
WGL Holdings, Inc.	'		'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'		'
Commercial Paper	453,500,000		373,100,000
Washington Gas Light Company	'		'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'		'
Commercial Paper	89,000,000		124,500,000
Carrying Amount | WGL Holdings, Inc.	'		'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'		'
Money Market Funds	9,700,000	[1]	6,500,000	[1]
Other Short Term Investments	0	[1]	100,000	[1]
Commercial Paper	453,500,000	[2]	373,100,000	[2]
Long-term debt	679,200,000	[3]	524,100,000	[3]
Carrying Amount | Washington Gas Light Company	'		'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'		'
Money Market Funds	4,300,000	[1]	3,100,000	[1]
Other Short Term Investments	0	[1]	100,000	[1]
Commercial Paper	89,000,000	[2]	124,500,000	[2]
Long-term debt	679,200,000	[3]	524,100,000	[3]
Fair Value | WGL Holdings, Inc.	'		'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'		'
Money Market Funds	9,700,000	[1]	6,500,000	[1]
Other Short Term Investments	0	[1]	100,000	[1]
Commercial Paper	453,500,000	[2]	373,100,000	[2]
Long-term debt	809,300,000	[3]	630,200,000	[3]
Fair Value | Washington Gas Light Company	'		'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'		'
Money Market Funds	4,300,000	[1]	3,100,000	[1]
Other Short Term Investments	0	[1]	100,000	[1]
Commercial Paper	89,000,000	[2]	124,500,000	[2]
Long-term debt	$809,300,000	[3]	$630,200,000	[3]
[1]	Balance located in cash and cash equivalents in the accompanying balance sheets. These amounts may be offset by outstanding checks.
[2]	Balance is located in notes payable in the accompanying balance sheets.
[3]	Less current maturities and unamortized discounts.

Fair_Value_Measurements_Quanti

Fair Value Measurements (Quantitative information WGLH) (Details) (WGL Holdings, Inc., USD $)

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Electricity Related Derivatives [Member]

Electricity Related Derivatives [Member]

Electricity Related Derivatives [Member]

Electricity Related Derivatives [Member]

Electricity Related Derivatives [Member]

Electricity Related Derivatives [Member]

Electricity Related Derivatives [Member]

Discounted Cash Flow [Member]

Discounted Cash Flow [Member]

Discounted Cash Flow [Member]

Discounted Cash Flow [Member]

Option Model [Member]

Option Model [Member]

Option Model [Member]

Option Model [Member]

Option Model [Member]

Option Model [Member]

Option Model [Member]

Option Model [Member]

Discounted Cash Flow [Member]

Discounted Cash Flow [Member]

Discounted Cash Flow [Member]

Discounted Cash Flow [Member]

Maximum [Member]

Maximum [Member]

Minimum [Member]

Minimum [Member]

Maximum [Member]

Maximum [Member]

Maximum [Member]

Maximum [Member]

Minimum [Member]

Minimum [Member]

Minimum [Member]

Minimum [Member]

Maximum [Member]

Maximum [Member]

Minimum [Member]

Minimum [Member]

Natural Gas Basis Price [Member]

Natural Gas Basis Price [Member]

Natural Gas Basis Price [Member]

Natural Gas Basis Price [Member]

Natural Gas Basis Price [Member]

Natural Gas Basis Price [Member]

Annualized Volatility Price [Member]

Annualized Volatility Price [Member]

Natural Gas Basis Price [Member]

Natural Gas Basis Price [Member]

Annualized Volatility Price [Member]

Annualized Volatility Price [Member]

Electricity Congestion Price [Member]

Electricity Congestion Price [Member]

Electricity Congestion Price [Member]

Electricity Congestion Price [Member]

Fair Value Measurements Details [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fair Value Measurement With Unobservable Inputs Reconciliations Recurring Basis Net Assets And Liability Value

($299,700,000)

($151,700,000)

$42,800,000

($294,700,000)

($155,200,000)

$39,600,000

'

'

'

'

'

'

'

'

'

'

'

'

($5,000,000)

$2,400,000

$2,800,000

'

'

'

'

Input Price

'

'

'

'

'

'

$6.15

$2.21

($2.10)

($1.78)

$6.15

$0.63

'

'

($1.68)

($0.18)

'

'

'

'

'

$90.95

$64.15

($2.85)

($2.00)

Option Volatility Percentage

'

'

'

'

'

'

'

'

'

'

'

'

589.60%

276.60%

'

'

30.90%

34.60%

'

'

'

'

'

'

'

Fair_Value_Measurements_Quanti1

Fair Value Measurements (Quantitative information WGL) (Details) (Washington Gas Light Company, USD $)

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Natural Gas Related Derivatives [Member]

Discounted Cash Flow [Member]

Discounted Cash Flow [Member]

Discounted Cash Flow [Member]

Discounted Cash Flow [Member]

Option Model [Member]

Option Model [Member]

Option Model [Member]

Option Model [Member]

Maximum [Member]

Maximum [Member]

Minimum [Member]

Minimum [Member]

Maximum [Member]

Maximum [Member]

Minimum [Member]

Minimum [Member]

Natural Gas Basis Price [Member]

Natural Gas Basis Price [Member]

Natural Gas Basis Price [Member]

Natural Gas Basis Price [Member]

Natural Gas Basis Price [Member]

Annualized Volatility Price [Member]

Natural Gas Basis Price [Member]

Annualized Volatility Price [Member]

Fair Value Measurements Details [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fair Value Measurement With Unobservable Inputs Reconciliations Recurring Basis Net Assets And Liability Value

($270,600,000)

($133,600,000)

$35,100,000

($270,600,000)

($133,600,000)

$35,600,000

'

'

'

'

'

'

'

'

Input Price

'

'

'

'

'

'

$6.15

$2.21

($2.10)

($1.78)

$0.63

'

$0.02

'

Option Volatility Percentage

'

'

'

'

'

'

'

'

'

'

'

276.60%

'

46.80%

Fair_Value_Measurements_Nonrec

Fair Value Measurements (Nonrecurring Basis) (Details) (USD $)

3 Months Ended

12 Months Ended

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2014

Sep. 30, 2013

Springfield Operations Center

Springfield Operations Center

WGL Holdings, Inc.

WGL Holdings, Inc.

WGL Holdings, Inc.

Washington Gas Light Company

Washington Gas Light Company

Washington Gas Light Company

Washington Gas Light Company

Washington Gas Light Company

Washington Gas Light Company

Washington Gas Light Company

Washington Gas Light Company

Springfield Operations Center

Springfield Operations Center

Springfield Operations Center

Abandoned LNG Facility

Abandoned LNG Facility

Fair Value Measurements [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

Carrying Amount Of Long Lived Assets Held For Use

'

'

'

'

'

'

'

'

$22,300,000

$24,900,000

$29,900,000

'

'

Fair Value Of Long Lived Assets Held For Use

'

'

'

'

'

'

'

'

21,500,000

22,300,000

24,900,000

'

'

Impairment loss

$800,000

$2,600,000

$2,639,000

$2,600,000

$5,015,000

$2,639,000

$2,600,000

$5,015,000

$800,000

$2,600,000

$5,000,000

$1,900,000

$500,000

Operating_Segment_Reporting_De

Operating Segment Reporting (Details) (USD $)

3 Months Ended

12 Months Ended

In Thousands, unless otherwise specified

Sep. 30, 2014

Jun. 30, 2014

Mar. 31, 2014

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Regulated Operation [Member]

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Operating Revenues

'

'

'

'

'

'

'

'

$1,443,800

[1]

$1,200,357

[1]

$1,137,666

[1]

Operating Expenses:

'

'

'

'

'

'

'

'

'

'

'

Cost of energy-related sales

'

'

'

'

'

'

'

'

726,879

521,508

421,539

Operation

'

'

'

'

'

'

'

'

234,391

243,341

227,362

Maintenance

'

'

'

'

'

'

'

'

56,972

49,269

52,494

Depreciation and amortization

'

'

'

'

'

'

'

'

104,064

100,438

94,998

Revenue taxes

'

'

'

'

'

'

'

'

84,287

81,422

74,244

Other

'

'

'

'

'

'

'

'

53,402

52,271

50,822

Total Operating Expenses

'

'

'

'

'

'

'

'

1,259,995

1,048,249

921,459

Operating Income (Loss), Total

'

'

'

'

'

'

'

'

183,805

152,108

216,207

Equity in earnings of unconsolidated affiliates

'

'

'

'

'

'

'

'

0

0

0

Other Income (Expense) - Net

'

'

'

'

'

'

'

'

863

1,539

3,085

Interest Expense

'

'

'

'

'

'

'

'

37,127

35,631

36,098

Dividends on Washington Gas Light Company preferred stock

'

'

'

'

'

'

'

'

1,320

1,320

1,320

INCOME TAX EXPENSE (BENEFIT)

'

'

'

'

'

'

'

'

48,181

44,883

72,178

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

'

'

'

'

'

'

'

'

98,040

71,813

109,696

Segment Reporting Information Additional Elements For Bank Presentation [Abstract]

'

'

'

'

'

'

'

'

'

'

'

Total Assets

3,979,522

'

'

'

3,486,296

'

'

'

3,979,522

3,486,296

3,516,046

Capital Expenditures

286,323

'

'

'

227,948

'

'

'

286,323

227,948

208,225

Equity Method Investments

0

'

'

'

0

'

'

'

0

0

0

Retail Energy Marketing [Member] | Unregulated Operation [Member]

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Operating Revenues

'

'

'

'

'

'

'

'

1,310,279

[1]

1,279,364

[1]

1,267,070

[1]

Operating Expenses:

'

'

'

'

'

'

'

'

'

'

'

Cost of energy-related sales

'

'

'

'

'

'

'

'

1,238,970

1,164,831

1,139,162

Operation

'

'

'

'

'

'

'

'

43,750

49,574

52,161

Maintenance

'

'

'

'

'

'

'

'

0

0

0

Depreciation and amortization

'

'

'

'

'

'

'

'

756

726

735

Revenue taxes

'

'

'

'

'

'

'

'

8,276

6,831

5,776

Other

'

'

'

'

'

'

'

'

4,615

4,411

4,070

Total Operating Expenses

'

'

'

'

'

'

'

'

1,296,367

1,226,373

1,201,904

Operating Income (Loss), Total

'

'

'

'

'

'

'

'

13,912

52,991

65,166

Equity in earnings of unconsolidated affiliates

'

'

'

'

'

'

'

'

1

0

0

Other Income (Expense) - Net

'

'

'

'

'

'

'

'

103

273

42

Interest Expense

'

'

'

'

'

'

'

'

10

13

1

Dividends on Washington Gas Light Company preferred stock

'

'

'

'

'

'

'

'

0

0

0

INCOME TAX EXPENSE (BENEFIT)

'

'

'

'

'

'

'

'

5,764

20,227

25,876

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

'

'

'

'

'

'

'

'

8,242

33,024

39,331

Segment Reporting Information Additional Elements For Bank Presentation [Abstract]

'

'

'

'

'

'

'

'

'

'

'

Total Assets

389,700

'

'

'

403,082

'

'

'

389,700

403,082

361,801

Capital Expenditures

76

'

'

'

730

'

'

'

76

730

984

Equity Method Investments

0

'

'

'

0

'

'

'

0

0

0

Commercial Energy Systems [Member] | Unregulated Operation [Member]

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Operating Revenues

'

'

'

'

'

'

'

'

40,679

[1]

35,217

[1]

60,325

[1]

Operating Expenses:

'

'

'

'

'

'

'

'

'

'

'

Cost of energy-related sales

'

'

'

'

'

'

'

'

20,348

24,450

51,149

Operation

'

'

'

'

'

'

'

'

10,419

6,875

5,414

Maintenance

'

'

'

'

'

'

'

'

0

0

0

Depreciation and amortization

'

'

'

'

'

'

'

'

6,178

2,411

1,261

Revenue taxes

'

'

'

'

'

'

'

'

5

7

8

Other

'

'

'

'

'

'

'

'

253

303

280

Total Operating Expenses

'

'

'

'

'

'

'

'

37,203

34,046

58,112

Operating Income (Loss), Total

'

'

'

'

'

'

'

'

3,476

1,171

2,213

Equity in earnings of unconsolidated affiliates

'

'

'

'

'

'

'

'

1,953

1,070

947

Other Income (Expense) - Net

'

'

'

'

'

'

'

'

1,007

778

-32

Interest Expense

'

'

'

'

'

'

'

'

0

234

1

Dividends on Washington Gas Light Company preferred stock

'

'

'

'

'

'

'

'

0

0

0

INCOME TAX EXPENSE (BENEFIT)

'

'

'

'

'

'

'

'

1,019

-206

760

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

'

'

'

'

'

'

'

'

5,417

2,991

2,367

Segment Reporting Information Additional Elements For Bank Presentation [Abstract]

'

'

'

'

'

'

'

'

'

'

'

Total Assets

521,570

'

'

'

318,995

'

'

'

521,570

318,995

148,407

Capital Expenditures

108,363

'

'

'

83,667

'

'

'

108,363

83,667

41,818

Equity Method Investments

66,810

'

'

'

54,977

'

'

'

66,810

54,977

23,346

Mistream Energy Services [Member] | Unregulated Operation [Member]

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Operating Revenues

'

'

'

'

'

'

'

'

16,555

[1]

-20,390

[1]

-11,221

[1]

Operating Expenses:

'

'

'

'

'

'

'

'

'

'

'

Cost of energy-related sales

'

'

'

'

'

'

'

'

0

0

0

Operation

'

'

'

'

'

'

'

'

8,517

8,683

2,860

Maintenance

'

'

'

'

'

'

'

'

0

0

0

Depreciation and amortization

'

'

'

'

'

'

'

'

124

124

116

Revenue taxes

'

'

'

'

'

'

'

'

0

0

0

Other

'

'

'

'

'

'

'

'

274

474

240

Total Operating Expenses

'

'

'

'

'

'

'

'

8,915

9,281

3,216

Operating Income (Loss), Total

'

'

'

'

'

'

'

'

7,640

-29,671

-14,437

Equity in earnings of unconsolidated affiliates

'

'

'

'

'

'

'

'

771

312

0

Other Income (Expense) - Net

'

'

'

'

'

'

'

'

-239

0

0

Interest Expense

'

'

'

'

'

'

'

'

0

417

0

Dividends on Washington Gas Light Company preferred stock

'

'

'

'

'

'

'

'

0

0

0

INCOME TAX EXPENSE (BENEFIT)

'

'

'

'

'

'

'

'

1,969

-10,951

-5,347

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

'

'

'

'

'

'

'

'

6,203

-18,825

-9,090

Segment Reporting Information Additional Elements For Bank Presentation [Abstract]

'

'

'

'

'

'

'

'

'

'

'

Total Assets

211,824

'

'

'

231,368

'

'

'

211,824

231,368

169,456

Capital Expenditures

0

'

'

'

0

'

'

'

0

0

101

Equity Method Investments

28,076

'

'

'

6,507

'

'

'

28,076

6,507

0

Other Activities [Member] | Unregulated Operation [Member]

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Operating Revenues

'

'

'

'

'

'

'

'

0

[1]

0

[1]

0

[1]

Operating Expenses:

'

'

'

'

'

'

'

'

'

'

'

Cost of energy-related sales

'

'

'

'

'

'

'

'

0

0

0

Operation

'

'

'

'

'

'

'

'

11,749

9,344

3,612

Maintenance

'

'

'

'

'

'

'

'

0

0

0

Depreciation and amortization

'

'

'

'

'

'

'

'

0

0

0

Revenue taxes

'

'

'

'

'

'

'

'

0

0

0

Other

'

'

'

'

'

'

'

'

84

97

16

Total Operating Expenses

'

'

'

'

'

'

'

'

11,833

9,441

3,628

Operating Income (Loss), Total

'

'

'

'

'

'

'

'

-11,833

-9,441

-3,628

Equity in earnings of unconsolidated affiliates

'

'

'

'

'

'

'

'

469

128

293

Other Income (Expense) - Net

'

'

'

'

'

'

'

'

-198

644

1,097

Interest Expense

'

'

'

'

'

'

'

'

601

402

366

Dividends on Washington Gas Light Company preferred stock

'

'

'

'

'

'

'

'

0

0

0

INCOME TAX EXPENSE (BENEFIT)

'

'

'

'

'

'

'

'

111

-1,124

-118

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

'

'

'

'

'

'

'

'

-12,274

-7,947

-2,486

Segment Reporting Information Additional Elements For Bank Presentation [Abstract]

'

'

'

'

'

'

'

'

'

'

'

Total Assets

369,816

'

'

'

290,440

'

'

'

369,816

290,440

211,038

Capital Expenditures

0

'

'

'

0

'

'

'

0

0

0

Equity Method Investments

16

'

'

'

413

'

'

'

16

413

0

Corporate Elimination [Member]

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Operating Revenues

'

'

'

'

'

'

'

'

-30,366

[1],[2]

-28,410

[1]

-28,530

[1],[2]

Operating Expenses:

'

'

'

'

'

'

'

'

'

'

'

Cost of energy-related sales

'

'

'

'

'

'

'

'

-30,613

[2]

-26,458

[2]

-26,802

[2]

Operation

'

'

'

'

'

'

'

'

75

[2]

-197

[2]

-1,093

[2]

Maintenance

'

'

'

'

'

'

'

'

0

[2]

0

[2]

0

[2]

Depreciation and amortization

'

'

'

'

'

'

'

'

-350

[2]

-415

[2]

-634

[2]

Revenue taxes

'

'

'

'

'

'

'

'

0

[2]

0

[2]

0

[2]

Other

'

'

'

'

'

'

'

'

0

[2]

0

[2]

-1

[2]

Total Operating Expenses

'

'

'

'

'

'

'

'

-30,888

[2]

-27,070

[2]

-28,530

[2]

Operating Income (Loss), Total

'

'

'

'

'

'

'

'

522

[2]

-1,340

[2]

0

[2]

Equity in earnings of unconsolidated affiliates

'

'

'

'

'

'

'

'

0

[2]

0

[2]

0

[2]

Other Income (Expense) - Net

'

'

'

'

'

'

'

'

0

[2]

-686

[2]

-38

[2]

Interest Expense

'

'

'

'

'

'

'

'

0

[2]

-686

[2]

-38

[2]

Dividends on Washington Gas Light Company preferred stock

'

'

'

'

'

'

'

'

0

[2]

0

[2]

0

[2]

INCOME TAX EXPENSE (BENEFIT)

'

'

'

'

'

'

'

'

210

[2]

-537

[2]

0

[2]

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

'

'

'

'

'

'

'

'

312

[2]

-803

[2]

0

[2]

Segment Reporting Information Additional Elements For Bank Presentation [Abstract]

'

'

'

'

'

'

'

'

'

'

'

Total Assets

-615,933

[2]

'

'

'

-470,121

[2]

'

'

'

-615,933

[2]

-470,121

[2]

-295,801

[2]

Capital Expenditures

0

[2]

'

'

'

0

[2]

'

'

'

0

[2]

0

[2]

0

[2]

Equity Method Investments

0

[2]

'

'

'

0

[2]

'

'

'

0

[2]

0

[2]

0

[2]

WGL Holdings, Inc.

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Operating Revenues

458,900

467,500

1,174,250

680,297

409,901

478,118

891,383

686,736

2,780,947

[1]

2,466,138

[1]

2,425,310

[1]

Operating Expenses:

'

'

'

'

'

'

'

'

'

'

'

Cost of energy-related sales

'

'

'

'

'

'

'

'

1,955,584

1,684,331

1,585,048

Operation

'

'

'

'

'

'

'

'

308,901

317,620

290,316

Maintenance

'

'

'

'

'

'

'

'

56,972

49,269

52,494

Depreciation and amortization

'

'

'

'

'

'

'

'

110,772

103,284

96,476

Revenue taxes

'

'

'

'

'

'

'

'

92,568

88,260

80,028

Other

'

'

'

'

'

'

'

'

58,628

57,556

55,427

Total Operating Expenses

'

'

'

'

'

'

'

'

2,583,425

2,300,320

2,159,789

Operating Income (Loss), Total

69,566

-9,489

104,733

32,712

-75,270

-9,111

155,584

94,616

197,522

165,818

265,521

Equity in earnings of unconsolidated affiliates

'

'

'

'

'

'

'

'

3,194

1,510

1,240

Other Income (Expense) - Net

'

'

'

'

'

'

'

'

1,536

2,548

4,154

Interest Expense

'

'

'

'

'

'

'

'

37,738

36,011

36,428

Dividends on Washington Gas Light Company preferred stock

'

'

'

'

'

'

'

'

1,320

1,320

1,320

INCOME TAX EXPENSE (BENEFIT)

'

'

'

'

'

'

'

'

57,254

52,292

93,349

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

38,038

-11,940

61,213

18,629

-51,625

-10,015

89,505

52,388

105,940

80,253

139,818

Segment Reporting Information Additional Elements For Bank Presentation [Abstract]

'

'

'

'

'

'

'

'

'

'

'

Total Assets

4,856,499

'

'

'

4,260,060

'

'

'

4,856,499

4,260,060

4,110,947

Capital Expenditures

394,762

'

'

'

312,345

'

'

'

394,762

312,345

251,128

Equity Method Investments

$94,902

'

'

'

$61,897

'

'

'

$94,902

$61,897

$23,346

[1]

Operating revenues are reported gross of revenue taxes. Revenue taxes of both the regulated utility and the retail energy-marketing segments include gross receipt taxes. Revenue taxes of the regulated utility segment also include PSC fees, franchise fees and energy taxes. Operating revenue amounts in the "Eliminations" column represent total intersegment revenues associated with sales from the regulated utility segment to the retail energy-marketing segment. Midstream Energy Services' cost of energy related sales is netted with its gross revenues.

[2]

Intersegment eliminations net income includes a timing difference between Commercial Energy Systems' recognition of revenue for the sale of Solar Renewable Energy Credits (SRECs) to Retail Energy-Marketing and Retail Energy's Marketing's recognition of the associate expense. Retail Energy-Marketing has recorded a portion of the SREC's purchased as inventory to be used in future periods at which time they will be expensed.

Other_Investments_Narratives_D

Other Investments - Narratives (Details) (USD $)	Sep. 30, 2014	Sep. 30, 2013
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Direct Fiinancing Leases Receivable	$22,000,000	'
WGL Holdings, Inc.	'	'
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Assets	72,600,000	120,300,000
Investments in direct financing leases, capital leases	18,159,000	23,390,000
Investments in unconsolidated affiliates	100,528,000	67,522,000
WGL Holdings, Inc. | Crab Run [Member]	'	'
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Investments in unconsolidated affiliates	0	'
WGL Holdings, Inc. | Warrant	'	'
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Assets	0	1,100,000
Willams Partners L.P. | Constitution [Member]	'	'
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Equity Method Investment Ownership Percentage	41.00%	'
Cabot Oil And Gas Corporation | Constitution [Member]	'	'
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Equity Method Investment Ownership Percentage	25.00%	'
Piedmont Natural Gas | Constitution [Member]	'	'
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Equity Method Investment Ownership Percentage	24.00%	'
COG Holdings LLC [Member] | Meade [Member]	'	'
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Equity Method Investment Ownership Percentage	20.00%	'
Vega Midstream MPC LLC [Member] | Meade [Member]	'	'
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Equity Method Investment Ownership Percentage	15.00%	'
River Road Interests LLC [Member] | Meade [Member]	'	'
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Equity Method Investment Ownership Percentage	10.00%	'
WGL Midstream | Constitution [Member]	'	'
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Estimated Investment In Constitution	72,000,000	'
Equity Method Investment Ownership Percentage	10.00%	'
Investments in unconsolidated affiliates	22,200,000	'
WGL Midstream | Meade [Member]	'	'
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Equity Method Investment Ownership Percentage	55.00%	'
Pipeline length in miles	177	'
Transportation and delivery	1.7	'
VIE Maximum Loss Exposure	74,000,000	'
Estimated Investment in Meade	410,000,000	'
Investments in unconsolidated affiliates	5,800,000	'
WGSW, Inc. [Member] | Sun Edison/Nextility [Member]	'	'
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Investments in direct financing leases, capital leases	19,900,000	29,200,000
Net Investment in Direct Financing Lease, Current	1,700,000	5,800,000
WGSW, Inc. [Member] | ASD Solar, LP [Member]	'	'
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Equity Method Investment Difference Between Carrying Amount and Underlying Equity	35,900,000	'
Investments in unconsolidated affiliates	66,800,000	'
Washington Gas Resources Corp. | American Solar Direct Holdings Inc. (ASDHI)	'	'
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]	'	'
Cost Method Investments	5,600,000	5,600,000
Warrants	$800,000	$1,900,000

Other_Investments_Financing_Le

Other Investments - Financing Leases Table (Details) (USD $)	Sep. 30, 2014
In Millions, unless otherwise specified
Capital Leases Future Minimum Payments Receivable [Abstract]	'
2015	$2.30
2016	2
2017	1.9
2018	1.8
2019	1.7
Thereafter	12.3
Total	22
Direct Financing Leases - Unearned Income	10.2
Direct Financing Leases - Residual Value	5.1
Direct Financing Leases - Initial Direct Costs	0.7
Direct Financing Leases - Tax Credits	$3

Other_Investments_Location_Tab

Other Investments - Location Table (Details) (USD $)	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
VIEs	'	'
ASSETS	'	'
Investments in unconsolidated affiliates	$72,600,000	$55,400,000
Investments in direct financing leases, capital leases	18,200,000	23,400,000
Deferred charges and other assets - derivatives	0	0
Net Investment in Direct Financing Lease, Current	1,700,000	5,800,000
Total assets	92,500,000	84,600,000
LIABILITIES	'	'
Other	'	8,500,000
Total liabilities	'	8,500,000
INCOME STATEMENT	'	'
Equity in earnings of unconsolidated affiliates	2,200,000	1,000,000
Depreciation and amortization	200,000	100,000
Other income - net	2,600,000	1,400,000
Net income	4,600,000	2,300,000
Non-VIEs	'	'
ASSETS	'	'
Investments in unconsolidated affiliates	27,900,000	12,100,000
Investments in direct financing leases, capital leases	0	0
Deferred charges and other assets - derivatives	0	1,100,000
Net Investment in Direct Financing Lease, Current	0	0
Total assets	27,900,000	13,200,000
LIABILITIES	'	'
Other	'	0
Total liabilities	'	0
INCOME STATEMENT	'	'
Equity in earnings of unconsolidated affiliates	1,000,000	500,000
Depreciation and amortization	0	0
Other income - net	0	0
Net income	1,000,000	500,000
Total	'	'
ASSETS	'	'
Investments in unconsolidated affiliates	100,500,000	67,500,000
Investments in direct financing leases, capital leases	18,200,000	23,400,000
Deferred charges and other assets - derivatives	0	1,100,000
Net Investment in Direct Financing Lease, Current	1,700,000	5,800,000
Total assets	120,400,000	97,800,000
LIABILITIES	'	'
Other	'	8,500,000
Total Liabilities	'	8,500,000
INCOME STATEMENT	'	'
Equity in earnings of unconsolidated affiliates	3,200,000	1,500,000
Depreciation and amortization	200,000	100,000
Other income - net	2,600,000	1,400,000
Net income	$5,600,000	$2,800,000

Related_Party_Transactions_Det

Related Party Transactions (Details) (USD $)	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
WGEServices	'	'	'
Related Party Transaction [Line Items]	'	'	'
Related Party Gas Imbalance - Receivable	$24,709	$1,000,000	'
Washington Gas Light Company	'	'	'
Related Party Transaction [Line Items]	'	'	'
Related Party Transaction, Revenues from Transactions with Related Party	26,600,000	25,000,000	26,800,000
Due from Related Parties, Current	4,800,000	7,200,000	'
Due to Related Parties, Current	54,700,000	20,600,000	'
Related Party Purchased Receivables	$7,700,000	$106,600,000	'

Changes_in_Accumulated_Other_C2

Changes in Accumulated Other Comprehensive Income Table (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
WGL Holdings, Inc.	'		'		'
Accumulated Other Comprehensive Income (Loss) Net Of Tax [Roll Forward]	'		'		'
Beginning Balance	($11,048)		($12,201)		'
Qualified cash flow hedging instruments	-1,548	[1]	0		0
Change in prior service cost (credit)	6,095	[2],[3]	-1,671	[2]	-640
Amortization of actuarial gain (loss)	1,594	[2]	3,399	[2]	-2,125
Amortization of transition obligation	0	[2]	238	[2]	239
Current-period other comprehensive income	6,141		1,966		-2,526
Income tax expense related to other comprehensive income	3,054	[3]	813		-987
Ending Balance	-7,961		-11,048		-12,201
Washington Gas Light Company	'		'		'
Accumulated Other Comprehensive Income (Loss) Net Of Tax [Roll Forward]	'		'		'
Beginning Balance	-11,048		-12,201		'
Change in prior service cost (credit)	6,095	[2],[3]	-1,671	[2]	-640
Amortization of actuarial gain (loss)	1,594	[2]	3,399	[2]	-2,125
Amortization of transition obligation	0	[2]	238	[2]	239
Current-period other comprehensive income	7,689		1,966		-2,526
Income tax expense related to other comprehensive income	3,054	[3]	813		-987
Ending Balance	($6,413)		($11,048)		($12,201)
[1]	(c ) Cash flow hedging instruments represent interest rate swap agreements on debt issuances. Refer to Note 14 - Derivative and Weather-related Instruments for further discussion of the interest rate swap agreements.
[2]	(a) These accumulated other comprehensive income components are included in the computation of net periodic benefit cost. Refer to Note 10-Pension and other post-retirement benefit plans for additional details.
[3]	(b) The majority of the 2014 change to the prior service cost component of other comprehensive income is related to the impact of the OPEB plan amendment and re-measurement. Refer to Note 10-Pension and other post-retirement benefit plans for additional details.

Subsequent_Events_Details

Subsequent Events (Details)	12 Months Ended
	Sep. 30, 2014
Debt Issuance [Member]	'
Subsequent Event [LineItems]	'
Subsequent Event Description	'Debt Issuance On October 24, 2014, WGL issued $100.0 million of 2.25% notes due November 1, 2019 (“2019 Notes”) and $125.0 million of 4.60% notes due November 1, 2044 (“2044 Notes”). The notes were priced at 99.792% and 99.226% of par, respectively. The first semiannual coupon payment date is May 1, 2015. The 2019 Notes have a make whole call provision that WGL may exercise at any time on or after October 24, 2014 and prior to October 1, 2019. At any time on or after October 1, 2019, the 2019 Notes may be called at 100% of the principal of such notes, plus accrued and unpaid interest. The 2044 Notes have a make whole call provision that WGL may exercise at any time on or after October 24, 2014 and prior to May 1, 2044. At any time on or after May 1, 2044, the 2044 Notes may be called at 100% of the principal of such notes, plus accrued and unpaid interest. In connection with the issuance of the 2044 Notes, WGL settled two forward starting swap hedges for $75.0 million and $50.0 million, both of which resulted in payments to the counterparties of $4.6 million and $3.1 million, respectively. Proceeds from the sale of these notes will be used by WGL to primarily fund the repurchase of outstanding securities of WGL and capital investments of its non-utility subsidiaries. These transactions were executed with Wells Fargo Securities, LLC, BB&T Capital Markets, TD Securities and CIBC World Markets as underwriters.
Security Ratings [Member]	'
Subsequent Event [LineItems]	'
Subsequent Event Description	'Security Ratings On October 15, 2014, Fitch Ratings downgraded WGL’s credit rating for its senior unsecured debt to “A” from “A+.” On October 22, 2014, Moody’s assigned an issue credit rating for WGL’s senior unsecured debt of “A3” and S&P assigned an issue credit rating for WGL’s senior unsecured debt of “A.”
Legal Matters [Member]	'
Subsequent Event [LineItems]	'
Subsequent Event Description	'Legal Matters As previously disclosed, WGL has been cooperating with a Department of Justice (“the Department”) investigation of some of the federal contracting activities of one of its non-utility subsidiaries, WGESystems. The Department’s investigation concerned certain American Recovery and Reinvestment Act projects bid out by the General Services Administration in 2010, in which WGESystems participated as a subcontractor to an 8(a) prime contractor under the Small Business Administration’s 8(a) Business Development Program. On November 18, 2014, WGESystems entered into a deferred prosecution agreement with the Department, which will resolve the investigation. The agreement is for a two-year period, and the Department will not pursue the prosecution of WGESystems if WGESystems discharges its obligations under the agreement during the two-year term of the agreement. Pursuant to the agreement, WGESystems will pay fines and monetary penalties totaling $2,587,261 to the Department and implement and maintain certain remedial measures specified in the agreement.

Quarterly_Financial_Informatio2

Quarterly Financial Information - Table (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
WGL Holdings, Inc.	'	'	'	'	'	'	'	'	'		'		'
Operating Revenues	$458,900	$467,500	$1,174,250	$680,297	$409,901	$478,118	$891,383	$686,736	$2,780,947	[1]	$2,466,138	[1]	$2,425,310	[1]
Operating Income (Loss)	69,566	-9,489	104,733	32,712	-75,270	-9,111	155,584	94,616	197,522		165,818		265,521
NET INCOME (LOSS) APPLICABLE TO COMMON STOCK	38,038	-11,940	61,213	18,629	-51,625	-10,015	89,505	52,388	105,940		80,253		139,818
Earnings Per Share [Abstract]	'	'	'	'	'	'	'	'	'		'		'
Basic	$0.74	($0.23)	$1.18	$0.36	($1)	($0.19)	$1.73	$1.01	$2.05		$1.55		$2.71
Diluted	$0.74	($0.23)	$1.18	$0.36	($1)	($0.19)	$1.73	$1.01	$2.05		$1.55		$2.71
Washington Gas Light Company	'	'	'	'	'	'	'	'	'		'		'
Operating Revenues	138,825	197,752	716,808	390,415	127,708	180,882	535,950	355,817	1,443,800		1,200,357		1,137,666
Operating Income (Loss)	24,530	4,326	88,038	65,229	-55,421	-368	134,358	72,037	182,123		150,606		214,756
NET INCOME (LOSS) APPLICABLE TO COMMON STOCK	$9,872	($521)	$49,176	$38,477	($39,789)	($4,531)	$76,935	$38,387	$97,004		$71,002		$108,726
[1]	Operating revenues are reported gross of revenue taxes. Revenue taxes of both the regulated utility and the retail energy-marketing segments include gross receipt taxes. Revenue taxes of the regulated utility segment also include PSC fees, franchise fees and energy taxes. Operating revenue amounts in the "Eliminations" column represent total intersegment revenues associated with sales from the regulated utility segment to the retail energy-marketing segment. Midstream Energy Services' cost of energy related sales is netted with its gross revenues.

Quarterly_Financial_Informatio3

Quarterly Financial Information - Narrative (Details) (USD $)	12 Months Ended			3 Months Ended		12 Months Ended		3 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Jun. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2013
	Washington Gas	Washington Gas	Washington Gas	Abandoned LNG storage project	Abandoned LNG storage project	Abandoned LNG storage project	Abandoned LNG storage project	Springfield Operations Center	Springfield Operations Center
Impairment loss	$2,639	$2,600	$5,015	$1,900	$500	$1,900	$500	$800	$2,600

Schedule_II_Details

Schedule II (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
WGL Holdings, Inc.	'		'		'
Valuation and Qualifying Accounts Disclosure [Line Items]	'		'		'
Valuation Allowances and Reserves, Beginning Balance	$20,433		$19,792		$17,969
Valuation Allowances and Reserves, Charged to Cost and Expense	15,874		9,527		18,316
Valuation Allowances and Reserves, Charged to Other Accounts	4,341	[1]	4,217	[1]	4,774	[1]
Valuation Allowances and Reserves, Deductions	17,307	[2]	13,103	[2]	21,267	[2]
Valuation Allowances and Reserves, Ending Balance	23,341		20,433		19,792
Washington Gas Light Company	'		'		'
Valuation and Qualifying Accounts Disclosure [Line Items]	'		'		'
Valuation Allowances and Reserves, Beginning Balance	17,498		17,129		15,863
Valuation Allowances and Reserves, Charged to Cost and Expense	12,004		7,024		12,794
Valuation Allowances and Reserves, Charged to Other Accounts	4,198	[1]	3,978	[1]	4,300	[1]
Valuation Allowances and Reserves, Deductions	14,491	[2]	10,633	[2]	15,828	[2]
Valuation Allowances and Reserves, Ending Balance	$19,209		$17,498		$17,129
[1]	Recoveries on receivables previously written off as uncollectible and unclaimed customer deposits, overpayments, etc., not refundable.
[2]	Includes deductions for purposes for which reserves were provided or revisions made of estimated exposure.