Washington Gas Light (WGLCP) 10-K20 Nov 132013 Q4 Annual reportFinancial data

Company Profile

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Oct. 31, 2013	Mar. 31, 2013
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-13	'	'
Amendment Flag	'false	'	'
Document Fiscal Year Focus	'2013	'	'
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	'	'	$2,266,658,547
Entity Common Stock, Shares Outstanding	'	51,809,755	'

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Sep. 30, 2013		Sep. 30, 2012
In Thousands, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012
Deferred Charges and Other Assets	'		'
Investment in direct financing leases, capital leases	$23,800		'
Capitalization	'		'
Long-Term Debt	524,100	[1]	'
Current Liabilities	'		'
Notes payable	-373,100		-247,700
WGL Holdings, Inc.	'		'
Property, Plant and Equipment	'		'
At original cost	4,118,149		3,807,036
Accumulated depreciation and amortization	-1,210,686		-1,139,623
Net property, plant and equipment	2,907,463		2,667,413
Current Assets	'		'
Cash and cash equivalents	3,478		10,263
Receivables	'		'
Accounts receivable	229,544		238,945
Gas costs and other regulatory assets	10,825		40,835
Unbilled revenues	98,598		109,919
Allowance for doubtful accounts	-20,433		-19,792
Net receivables	318,534		369,907
Materials and supplies-principally at average cost	24,904		23,843
Storage gas	347,291		283,008
Deferred income taxes	24,522		12,404
Other prepayments	54,372		80,240
Derivatives	35,315		43,196
Other	11,595		9,900
Total current assets	820,011		832,761
Deferred Charges and Other Assets	'		'
Gas costs	93,963		0
Pension and other post-retirement benefits	240,793		435,118
Other	65,851		68,431
Derivatives	26,306		61,751
Investment in direct financing leases, capital leases	23,390		2,664
Investment in unconsolidated affiliates	67,522		29,256
Other	14,761		13,553
Total deferred charges and other assets	532,586		610,773
Total Assets	4,260,060		4,110,947
Capitalization	'		'
Common shareholders' equity	1,274,545		1,269,556
Washington Gas Light Company preferred stock	28,173		28,173
Long-Term Debt	524,067		589,202
Total capitalization	1,826,785		1,886,931
Current Liabilities	'		'
Current maturities of long-term debt	67,000		18
Notes payable	373,100		247,700
Accounts payable and other accrued liabilities	270,658		270,387
Wages payable	18,645		16,886
Accrued interest	3,399		3,524
Dividends declared	22,075		20,975
Customer deposits and advance payments	67,154		89,320
Gas costs and other regulatory liabilities	27,013		20,664
Accrued taxes	16,056		23,036
Derivatives	48,413		36,459
Other	36,564		28,046
Total current liabilities	950,077		757,015
Deferred Credits	'		'
Unamortized investment tax credits	46,378		25,260
Deferred income taxes	629,807		621,451
Accrued pensions and benefits	148,890		313,504
Asset retirement obligations	101,321		71,415
Regulatory liabilities	'		'
Gas costs	0		19,511
Accrued asset removal costs	321,266		325,618
Other	13,459		15,047
Derivatives	141,334		13,208
Other	80,743		61,987
Total deferred credits	1,483,198		1,467,001
Total Capitalization and Liabilities	4,260,060		4,110,947
Washington Gas Light Company	'		'
Property, Plant and Equipment	'		'
At original cost	3,903,482		3,686,192
Accumulated depreciation and amortization	-1,178,600		-1,111,796
Net property, plant and equipment	2,724,882		2,574,396
Current Assets	'		'
Cash and cash equivalents	0		1
Receivables	'		'
Accounts receivable	91,405		99,514
Gas costs and other regulatory assets	10,825		40,835
Unbilled revenues	19,418		19,300
Allowance for doubtful accounts	-17,498		-17,129
Net receivables	104,150		142,520
Materials and supplies-principally at average cost	24,857		23,797
Storage gas	132,226		114,826
Deferred income taxes	27,000		14,416
Other prepayments	22,794		55,255
Receivables from associated companies	7,173		5,532
Derivatives	4,278		9,206
Other	0		1,451
Total current assets	322,478		367,004
Deferred Charges and Other Assets	'		'
Gas costs	93,963		0
Pension and other post-retirement benefits	239,594		432,168
Other	65,824		68,429
Derivatives	16,051		50,973
Other	11,597		10,295
Total deferred charges and other assets	427,029		561,865
Total Assets	3,474,389		3,503,265
Capitalization	'		'
Common shareholders' equity	1,024,583		1,025,743
Washington Gas Light Company preferred stock	28,173		28,173
Long-Term Debt	524,067		589,202
Total capitalization	1,576,823		1,643,118
Current Liabilities	'		'
Current maturities of long-term debt	67,000		18
Notes payable	124,500		98,800
Accounts payable and other accrued liabilities	132,814		142,193
Wages payable	17,057		15,827
Accrued interest	3,399		3,524
Dividends declared	19,359		18,912
Customer deposits and advance payments	67,154		89,320
Gas costs and other regulatory liabilities	27,013		20,664
Accrued taxes	25,380		19,108
Payables to associated companies	20,557		28,540
Derivatives	24,749		10,512
Other	9,047		5,136
Total current liabilities	538,029		452,554
Deferred Credits	'		'
Unamortized investment tax credits	7,354		8,249
Deferred income taxes	611,453		605,938
Accrued pensions and benefits	147,479		310,605
Asset retirement obligations	99,972		70,141
Regulatory liabilities	'		'
Gas costs	0		19,511
Accrued asset removal costs	321,266		325,618
Other	13,459		15,047
Derivatives	106,144		3,507
Other	52,410		48,977
Total deferred credits	1,359,537		1,407,593
Total Capitalization and Liabilities	$3,474,389		$3,503,265

[1]	Excludes unamortized discounts of $29,907 at September 30, 2013.

Consolidated_Statements_of_Inc

Consolidated Statements of Income (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2011
WGL Holdings, Inc.	'		'		'
OPERATING REVENUES	'		'		'
Utility	$1,174,724		$1,109,355		$1,264,580
Non-utility	1,291,414		1,315,955		1,486,921
Total Operating Revenues	2,466,138	[1]	2,425,310	[1]	2,751,501	[1]
OPERATING EXPENSES	'		'		'
Utility cost of gas	496,487		394,955		595,678
Non-utility cost of energy-related sales	1,187,844		1,190,093		1,334,773
Operation and maintenance	366,367		342,348		339,529
Depreciation and amortization	103,284		96,476		91,325
General taxes and other assessments	145,816		135,455		146,421
Total Operating Expenses	2,299,798		2,159,327		2,507,726
OPERATING INCOME (LOSS)	166,340		265,983		243,775
Equity in earnings of unconsolidated affiliates	1,510		1,240		-549
Other Income (Expense) - Net	2,026		3,692		2,840
Interest Expense	36,011		36,428		40,546
INCOME (LOSS) BEFORE INCOME TAXES	133,865		234,487		205,520
INCOME TAX EXPENSE (BENEFIT)	52,292		93,349		87,150
Net income	81,573		141,138		118,370
Dividends on Washington Gas preferred stock	1,320		1,320		1,320
NET INCOME (LOSS) APPLICABLE TO COMMON STOCK	80,253		139,818		117,050
AVERAGE COMMON SHARES OUTSTANDING	'		'		'
Basic	51,697		51,522		51,195
Diluted	51,808		51,589		51,295
EARNINGS PER AVERAGE COMMON SHARE	'		'		'
Basic	$1.55		$2.71		$2.29
Diluted	$1.55		$2.71		$2.28
DIVIDENDS DECLARED PER COMMON SHARE	$1.66		$1.59		$1.54
Washington Gas Light Company	'		'		'
OPERATING REVENUES	'		'		'
Total Operating Revenues	1,200,357		1,137,666		1,288,539
OPERATING EXPENSES	'		'		'
Utility cost of gas	521,508		421,539		619,637
Operation and maintenance	295,137		282,234		280,463
Depreciation and amortization	99,188		93,811		89,116
General taxes and other assessments	133,391		124,814		136,079
Total Operating Expenses	1,049,224		922,398		1,125,295
OPERATING INCOME (LOSS)	151,133		215,268		163,244
Other Income (Expense) - Net	1,017		2,623		2,594
Interest Expense	35,631		36,098		40,462
INCOME (LOSS) BEFORE INCOME TAXES	116,519		181,793		125,376
INCOME TAX EXPENSE (BENEFIT)	44,197		71,747		55,786
Net income	72,322		110,046		69,590
Dividends on Washington Gas preferred stock	1,320		1,320		1,320
NET INCOME (LOSS) APPLICABLE TO COMMON STOCK	$71,002		$108,726		$68,270

[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, 2013	Sep. 30, 2012	Sep. 30, 2011
WGL Holdings, Inc.	'	'	'
Net Income	$81,573	$141,138	$118,370
Pension and other postretirement benefit plans	'	'	'
Change in prior service cost (credit)	-1,671	-640	135
Change in actuarial net gain (loss)	3,399	-2,125	-3,743
Change in transition obligation	238	239	5
Total pension and other postretirement benefit plans	1,966	-2,526	-3,603
INCOME TAX EXPENSE (BENEFIT) RELATED TO OTHER COMPREHENSIVE INCOME	813	-987	-1,512
OTHER COMPREHENSIVE INCOME (LOSS)	1,153	-1,539	-2,091
COMPREHENSIVE INCOME	82,726	139,599	116,279
Washington Gas Light Company	'	'	'
Net Income	72,322	110,046	69,590
Pension and other postretirement benefit plans	'	'	'
Change in prior service cost (credit)	-1,671	-640	135
Change in actuarial net gain (loss)	3,399	-2,125	-3,743
Change in transition obligation	238	239	5
Total pension and other postretirement benefit plans	1,966	-2,526	-3,603
INCOME TAX EXPENSE (BENEFIT) RELATED TO OTHER COMPREHENSIVE INCOME	813	-987	-1,512
OTHER COMPREHENSIVE INCOME (LOSS)	1,153	-1,539	-2,091
COMPREHENSIVE INCOME	$73,475	$108,507	$67,499

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
WGL Holdings, Inc.	'	'	'
OPERATING ACTIVITIES	'	'	'
Net income	$81,573	$141,138	$118,370
ADJUSTMENTS TO RECONCILE NET INCOME TO NET CASH PROVIDED BY OPERATING ACTIVITIES	'	'	'
Depreciation and amortization	103,284	96,476	91,325
Amortization of:	'	'	'
Other regulatory assets and liabilities-net	574	881	9,143
Debt related costs	873	894	915
Deferred income taxes-net	1,431	107,699	58,694
Accrued/deferred pension cost	36,127	-60,459	17,507
Compensation expense related to equity awards	3,050	4,122	2,277
Provision for doubtful accounts	9,258	18,316	18,080
Other non-cash charges (credits)-net	21,832	9,585	860
CHANGES IN ASSETS AND LIABILITIES	'	'	'
Accounts receivable and unbilled revenues-net	12,105	-65,329	-20,641
Gas costs and other regulatory assets/liabilities-net	36,359	-13,650	2,300
Storage gas	-64,283	7,386	-48,171
Other prepayments	25,868	-16,401	32,350
Accounts payable and other accrued liabilities	2,017	-16,683	34,475
Wages payable	1,759	-63	538
Customer deposits and advance payments	-22,166	11,181	12,796
Accrued taxes	-6,980	6,111	2,097
Accrued interest	-125	-356	-103
Other current assets	5,125	-26,010	544
Other current liabilities	20,472	27,716	-21,323
Deferred gas costs-net	-113,474	36,309	-10,807
Deferred assets-other	-1,411	-45,292	38,921
Deferred liabilities-other	-6,647	-4,583	-29,368
Derivatives-deferred	163,571	-1,858	-15,780
Other-net	5,232	-4,546	682
Net Cash Provided by (Used in) Operating Activities	318,024	217,599	295,681
FINANCING ACTIVITIES	'	'	'
Common stock issued	0	631	4,980
Long-term debt issued	4,157	0	75,000
Long-term debt retired	-2,295	-77,000	-30,000
Debt issuance costs	0	-123	-186
Notes payable issued (retired)-net	125,400	208,279	-61,018
Dividends on common stock and preferred stock	-86,078	-77,182	-74,266
Other financing activities-net	5,156	564	-390
Net Cash Provided by (Used in) Financing Activities	46,340	55,169	-85,880
INVESTING ACTIVITIES	'	'	'
Capital expenditures (excluding AFUDC)	-312,345	-251,128	-201,540
Investments in non-utility interests	-62,894	-24,636	-13,293
Distributions from non-utility interests	4,090	8,927	515
Net Cash Used in Investing Activities	-371,149	-266,837	-214,318
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	-6,785	5,931	-4,517
Cash and Cash Equivalents at Beginning of Year	10,263	4,332	8,849
Cash and Cash Equivalents at End of Year	3,478	10,263	4,332
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION	'	'	'
Income taxes paid (refunded) - net	-10,741	23,915	-5,974
Interest paid	35,471	36,777	40,612
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING ACTIVITIES	'	'	'
Project debt financing activities - net	1,386	2,004	-3,539
Capital expenditure accruals included in accounts payable and other accrued liabilities	32,040	34,980	27,472
Dividends paid in common stock	6,863	5,260	5,356
WGL Holdings, Inc. \| Springfield Operations Center	'	'	'
Amortization of:	'	'	'
Impairment loss	2,600	5,015	0
Washington Gas Light Company	'	'	'
OPERATING ACTIVITIES	'	'	'
Net income	72,322	110,046	69,590
ADJUSTMENTS TO RECONCILE NET INCOME TO NET CASH PROVIDED BY OPERATING ACTIVITIES	'	'	'
Depreciation and amortization	99,188	93,811	89,116
Amortization of:	'	'	'
Other regulatory assets and liabilities-net	911	881	9,143
Debt related costs	527	894	915
Deferred income taxes-net	-2,915	89,132	40,102
Accrued/deferred pension cost	35,707	-58,645	17,364
Compensation expense related to equity awards	2,292	3,394	2,651
Provision for doubtful accounts	7,183	12,794	14,028
Other non-cash charges (credits)-net	7,615	-2,726	-1,693
CHANGES IN ASSETS AND LIABILITIES	'	'	'
Accounts receivable and unbilled revenues-net	-464	-19,041	-30,912
Gas costs and other regulatory assets/liabilities-net	36,359	-13,650	2,300
Storage gas	-17,400	51,228	3,213
Other prepayments	32,461	-24,654	31,205
Accounts payable and other accrued liabilities	-24,949	27,214	-8,198
Wages payable	1,230	-204	519
Customer deposits and advance payments	-22,166	11,181	14,796
Accrued taxes	6,272	-3,721	9,552
Accrued interest	-125	-356	-103
Other current assets	5,319	-4,928	2,118
Other current liabilities	18,148	4,236	-8,302
Deferred gas costs-net	-113,474	36,309	-10,807
Deferred assets-other	-1,989	-36,963	30,247
Deferred liabilities-other	-3,995	-19,691	-33,813
Derivatives-deferred	137,559	-3,608	6,683
Other-net	-4,167	-1,673	180
Net Cash Provided by (Used in) Operating Activities	274,049	256,275	249,894
FINANCING ACTIVITIES	'	'	'
Long-term debt issued	4,157	0	75,000
Long-term debt retired	-2,295	-77,000	-30,000
Debt issuance costs	0	0	-186
Notes payable issued (retired)-net	25,700	98,778	-43,419
Dividends on common stock and preferred stock	-76,522	-75,239	-74,256
Other financing activities-net	336	2,533	-376
Net Cash Provided by (Used in) Financing Activities	-48,624	-50,928	-73,237
INVESTING ACTIVITIES	'	'	'
Capital expenditures (excluding AFUDC)	-225,426	-206,699	-179,694
Net Cash Used in Investing Activities	-225,426	-206,699	-179,694
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	-1	-1,352	-3,037
Cash and Cash Equivalents at Beginning of Year	1	1,353	4,390
Cash and Cash Equivalents at End of Year	0	1	1,353
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION	'	'	'
Income taxes paid (refunded) - net	-15,799	29,625	-8,537
Interest paid	35,091	36,447	40,528
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING ACTIVITIES	'	'	'
Project debt financing activities - net	1,386	2,004	-3,539
Capital expenditure accruals included in accounts payable and other accrued liabilities	16,429	22,909	22,339
Washington Gas Light Company \| Springfield Operations Center	'	'	'
Amortization of:	'	'	'
Impairment loss	$2,600	$5,015	$0

Consolidated_Statement_of_Capi

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

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

In Thousands, unless otherwise specified

Series One [Member]

Series Two [Member]

Series Three [Member]

Due fiscal year 2014

Due fiscal year 2015

Due fiscal year 2016

Due fiscal year 2019

Due fiscal year 2020

Due fiscal year 2023

Due fiscal year 2025

Due fiscal year 2027

Due fiscal year 2028

Due fiscal year 2030

Due fiscal year 2036

Due fiscal year 2040

Common Shareholders' Equity

Common stock, value

$574,461

$567,598

Paid-in capital

10,710

8,132

Retained Earnings

700,422

706,027

Accumulated Other Comprehensive Income (Loss), Net of Tax

-11,048

-12,201

Total Common shareholders' Equity

1,274,545

1,269,556

CommonShareholdersEquityAsPercentageOfTotalCapitalization

69.80%

67.30%

Preferred Stock

Washington Gas Light Company preferred stock

28,173

15,000

7,173

6,000

Preferred stock, percentage of total capitalization

1.50%

Long-Term Debt

Medium Term Notes

583,000

67,000

20,000

25,000

50,000

20,000

40,500

125,000

52,000

8,500

50,000

75,000

Maximum Note Rate Range

5.17%

4.83%

5.17%

7.46%

4.76%

6.65%

5.44%

6.82%

6.85%

7.50%

5.78%

5.21%

Minimum Note Rate Range

4.88%

4.83%

5.17%

7.46%

4.76%

6.65%

5.44%

6.40%

6.57%

7.50%

5.70%

5.21%

Other long-term debt

8,097

6,253

Unamortized discount

-30

-33

Less-current maturities

67,000

Long-Term Debt

524,067

589,202

LongTermDebtAsPercentageOfTotalCapitalization

28.70%

31.20%

Capitalization, Long-term Debt and Equity

$1,826,785

$1,886,931

Total Capitalization As Percentage

100.00%

Consolidated_Statement_of_Capi1

Consolidated Statement of Capitalization - WGLH (Parenthetical) (WGL Holdings, Inc., USD $)	Sep. 30, 2013	Sep. 30, 2012
Common Shareholders' Equity	'	'
Common Stock, Par or Stated Value Per Share	$0	$0
Preferred Stock [Abstract]	'	'
Preferred Stock, Shares Authorized	1,500,000	1,500,000
Preferred Stock [Member]	'	'
Preferred Stock [Abstract]	'	'
Preferred Stock, Shares Authorized	3,000,000	3,000,000
Preferred Stock, Issued	0	0
Common Stock [Member]	'	'
Common Shareholders' Equity	'	'
Common Stock, Shares Authorized	120,000,000	120,000,000
Common Stock, Shares, Issued	51,774,204	51,611,647
Series One [Member]	'	'
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]	'	'
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]	'	'
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, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

In Thousands, unless otherwise specified

Series One [Member]

Series Two [Member]

Series Three [Member]

Due fiscal year 2014

Due fiscal year 2015

Due fiscal year 2016

Due fiscal year 2019

Due fiscal year 2020

Due fiscal year 2023

Due fiscal year 2025

Due fiscal year 2027

Due fiscal year 2028

Due fiscal year 2030

Due fiscal year 2036

Due fiscal year 2040

Common Shareholders' Equity

Common stock, value

$46,480

$46,479

Paid-in capital

477,968

475,634

Retained Earnings

511,183

515,831

Accumulated Other Comprehensive Income (Loss), Net of Tax

-11,048

-12,201

Total Common shareholders' Equity

1,024,583

1,025,743

CommonShareholdersEquityAsPercentageOfTotalCapitalization

65.00%

62.40%

Preferred Stock

Noncontrolling Interest, Amount Represented by Preferred Stock

28,173

15,000

7,173

6,000

Preferred Stock As Percentage Of Total Capitalization

1.80%

1.70%

Long-Term Debt

Medium Term Notes

583,000

67,000

20,000

25,000

50,000

20,000

40,500

125,000

52,000

8,500

50,000

75,000

Maximum Note Rate Range

5.17%

4.83%

5.17%

7.46%

4.76%

6.65%

5.44%

6.82%

6.85%

7.50%

5.78%

5.21%

Minimum Note Rate Range

4.88%

4.83%

5.17%

7.46%

4.76%

6.65%

5.44%

6.40%

6.57%

7.50%

5.70%

5.21%

Other Long-term Debt

8,097

6,253

Unamortized discount

-30

-33

Less-current maturities

67,000

Long-Term Debt

524,067

589,202

LongTermDebtAsPercentageOfTotalCapitalization

33.20%

35.90%

Capitalization, Long-term Debt and Equity

$1,576,823

$1,643,118

Total Capitalization As Percentage

100.00%

Consolidated_Statement_of_Capi3

Consolidated Statement of Capitalization - WGL (Parenthetical) (Washington Gas Light Company, USD $)	Sep. 30, 2013	Sep. 30, 2012
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
Series One [Member]	'	'
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]	'	'
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]	'	'
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, 2010	$1,153,395	$543,121	$8,889	$609,956	($8,571)
Beginning Balance, shares at Sep. 30, 2010	'	50,974,992	'	'	'
Net Income	118,370	'	'	118,370	'
OTHER COMPREHENSIVE INCOME (LOSS)	-2,091	'	'	'	-2,091
Dividend Reinvestment	6,236	6,236	'	'	'
Dividend Reinvestment, Shares	'	163,461	'	'	'
Stock-based compensation	7,079	8,237	-1,158	'	'
Stock-based compensation, Share	'	226,884	'	'	'
Dividends declared:	'	'	'	'	'
Common Stock	-78,954	'	'	-78,954	'
Preferred Stock	-1,320	'	'	-1,320	'
Common shareholders' equity, ending balance at Sep. 30, 2011	1,202,715	557,594	7,731	648,052	-10,662
Ending 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	'	'	'
Stock-based compensation	4,088	3,687	401	'	'
Stock-based compensation, Share	'	93,875	'	'	'
Dividends declared:	'	'	'	'	'
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	'	'	'
Stock-based compensation	3,187	609	2,578	'	'
Stock-based compensation, Share	'	16,637	'	'	'
Dividends declared:	'	'	'	'	'
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	'	'	'

Consolidated_Statements_of_Com2

Consolidated Statements of Common Shareholders Equity (Parenthetical) - WGLH (WGL Holdings, Inc., USD $)	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
WGL Holdings, Inc.	'	'	'
DIVIDENDS DECLARED PER COMMON SHARE	$1.66	$1.59	$1.54

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, 2010		$994,876	$46,479	$470,825	$486,143	($8,571)
Beginning Balance, shares at Sep. 30, 2010		'	46,479,536	'	'	'
Net Income		69,590	'	'	69,590	'
OTHER COMPREHENSIVE INCOME (LOSS)		-2,091	'	'	'	-2,091
Stock-based compensation	[1]	2,274	'	2,274	'	'
Dividends declared:		'	'	'	'	'
Common Stock		-73,194	'	'	-73,194	'
Preferred Stock		-1,320	'	'	-1,320	'
Common shareholders' equity, ending balance at Sep. 30, 2011		990,135	46,479	473,099	481,219	-10,662
Ending 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	'	'	'

[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, 2013
Accounting Policies [Abstract]	'
Organization Consolidation And Presentation Of Financial Statements Disclosure Text Block	'
	NOTE 1. ACCOUNTING POLICIES
	GENERAL
	WGL Holdings, Inc. (WGL Holdings) 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 Holdings,” “we,” “us” or “our” refers to the holding company or the consolidated entity of WGL Holdings and all of its subsidiaries. Unless otherwise noted, these notes apply equally to WGL Holdings 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 74.7% of the total therms delivered to customers by Washington Gas in fiscal year September 30, 2013. Deliveries to interruptible customers accounted for 15.2% and deliveries to customers who use natural gas to generate electricity accounted for 10.1%. 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 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 and industrial 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 power generating facilities at September 30, 2013, 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, 2013, WGEServices served approximately 168,000 natural gas customers and approximately 180,000 electricity customers located in Maryland, Virginia, Delaware, Pennsylvania and the District of Columbia.

	The commercial energy systems segment consists of WGESystems, which provides commercial energy efficient and sustainable solutions to government and commercial clients under construction contracts. WGESystems is also increasing its investments in commercial solar, energy efficiency, and combined heat and power projects, that we (or an affiliate company) own and manage directly. This expansion includes the ownership and management of its renewable energy producing assets. In addition, this segment comprises the operations of WGSW, which holds investments in alternative energy assets. These investments are part of our long-term commitment to providing clean and efficient energy solutions to our customers and communities in select markets across the United States.

	The midstream energy services segment, which consists of the operations of WGL Midstream, engages in acquiring, managing and optimizing natural gas storage and transportation assets. 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 Holdings 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.
	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) is stated at original cost, including labor, materials, taxes and overhead costs incurred during the construction period. The cost of utility and other 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, 2013, 2012 and 2011 were 5.43%, 7.40% and 5.50%, respectively. Due to lower construction balances and significant decreases in short-term debt interest rates during fiscal year ended September 30, 2013, Washington Gas decreased capitalized AFUDC by $0.6 million. During fiscal year ended September 30, 2012, Washington Gas increased capitalized AFUDC by $0.7 million.
	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 2.86%, 2.87% and 2.84% during fiscal years 2013, 2012 and 2011, 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. Refer to Note 13—Commitments and Contingencies for a discussion of depreciation-related contingencies.
	At September 30, 2013 and 2012, 95.6% and 97.7%, respectively, of WGL Holdings' 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,		2013			2012
	($ In millions)		Dollars	%		Dollars	%
	Regulated utility segment
	Distribution, transmission and storage	$	3,356.10	81.5	$	3,176.40	83.4
	General, miscellaneous and intangibles		430.6	10.4		428.3	11.3
	Construction work in progress (CWIP)		150.8	3.7		113.2	3
	Total regulated utility segment		3,937.50	95.6		3,717.90	97.7
	Unregulated segments		180.6	4.4		89.1	2.3
	Total	$	4,118.10	100	$	3,807.00	100
	IMPAIRMENT OF LONG-LIVED ASSETS
	Management regularly reviews property and equipment and other long-lived assets, including certain definite-lived intangible assets, 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.
	At September 30, 2013, Washington Gas recorded a $0.5 million impairment loss for the unrecoverable portion of the Chillum LNG storage facility. At September 30, 2013 and 2012, Washington Gas applied a discounted cash value model to the anticipated proceeds from a future sale of its Springfield Operations Center and recorded an impairment charge of $2.6 million and $5.0 million, respectively, in operation and maintenance expense.. Washington Gas is actively marketing the unused operations facility for sale.
	OPERATING LEASES
	We have classified the lease of our corporate headquarters as an operating lease. We amortize to 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 Holdings or our subsidiaries as of September 30, 2013 and 2012.

	REVENUE AND COST RECOGNITION

	Regulated Utility Operations

	Revenues. For regulated deliveries of natural gas, Washington Gas reads meters and bills customers on a 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 on 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 delivered 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. The customer portion does not affect earnings.
	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 construction contracts using the percentage-of-completion method in “Operating Revenues—Non-utility” and “Non-Utility cost of energy-related sales.” Commercial Energy Systems also recognizes income from its solar assets based on the terms of the related power purchase agreements. WGSW recognizes income on its investments in solar 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 solar assets associated with the Skyline and EchoFirst associations.
	Midstream Energy Sevices 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 will recognize income on its investment using the cost approach of investment 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 years ended September 30, 2013, 2012 and 2011, WGL Holdings recorded a reduction of net income of $10.1 million, $22.4 million and $0.8 million, respectively, for lower-of-cost or market adjustment.
In conjunction with optimizing Washington Gas' storage capacity, storage gas inventory may be subject to lower-of-cost or market adjustments. Washington Gas did not record any lower-of-cost or market adjustments related to its storage gas inventory for the fiscal year ended September 30, 2013. For the fiscal years ended 2012 and 2011, Washington Gas recorded a lower-of-cost or market adjustment related to its storage gas inventory, after the effects of regulatory sharing of $1.4 million and $0.3 million, respectively, which was recorded to “Utility cost of gas.”
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 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, 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 substantially to lock-in operating margins that Washington Gas will 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 will ultimately 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, Derivatives and Hedging. 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.
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, 2013 and 2012. 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 (ASC Topic 718) 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 asset retirement obligations (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)		2013		2012
	Asset retirement obligations at beginning of year	$	72.7	$	69.5
	Liabilities incurred in the period		1.2		1.9
	Liabilities settled in the period		-1		-1
	Accretion expense		3.3		3.3
	Revisions in estimated cash flows^(a)		27.8		-1
	Asset retirement obligations at the end of the year^(b)	$	104	$	72.7

	Washington Gas Light Company
	Changes in Asset Retirement Obligations
			September 30,
	(In millions)		2013		2012
	Asset retirement obligations at beginning of year	$	71.5	$	68.3
	Liabilities incurred in the period		1.1		1.9
	Liabilities settled in the period		-1		-1
	Accretion expense		3.3		3.3
	Revisions in estimated cash flows^(a)		27.8		-1
	Asset retirement obligations at the end of the year^(b)	$	102.7	$	71.5
	(a) WGL revised its assumptions regarding the timing and amounts related to its obligation to cut, cap and purge pipeline. The revision is primarily driving by our accelerated pipeline replacement programs.
	(b) Includes short-term asset retirement obligations of $2.7 million and $1.3 million for fiscal year 2013 and 2012, respectively.
ACCOUNTING STANDARDS ADOPTED IN FISCAL YEAR 2013
Comprehensive Income. In June 2011, the FASB issued ASU 2011-05, Comprehensive Income (Topic 220): Presentation of Comprehensive Income. ASU 2011-05 intended to improve financial reporting by requiring companies to present items of net income in either one continuous statement, or in two separate but consecutive statements of net income and other comprehensive income. The new guidance removed the current presentation options in ASC Topic 220. The requirements of ASU 2011-05 did not change the components of comprehensive income that are recognized in net income or other comprehensive income, nor did the update change the computation of earnings per share (EPS). In December 2011, the FASB issued ASU 2011-12, Comprehensive Income (Topic 220): Deferral of the Effective Date for Amendments to the Presentation of Reclassifications of Items Out of Accumulated Other Comprehensive Income in Accounting Standards Update No. 2011-05. ASU 2011-12 indefinitely deferred the provisions requiring reclassification adjustments out of other comprehensive income (OCI) to be presented on the face of the financial statements. ASU 2011-05, as amended by ASU 2011-12, was effective for us on October 1, 2012. As a result of the standard, we presented comprehensive income in two separate but consecutive statements of net income and other comprehensive income. The adoption of this standard did not have a material effect on our financial statements.

OTHER NEWLY ISSUED ACCOUNTING STANDARDS
Balance Sheet Offsetting. In December 2011, the FASB issued ASU 2011-11, Disclosures about Offsetting Assets and Liabilities. This standard amends the disclosure requirements on offsetting in ASC Topic 210 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. In January 2013, the FASB issued ASU 2013-01, Clarifying the Scope of the Disclosures about Offsetting Assets and Liabilities. ASU 2013-01 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 2011-11 and ASU 2013-01 will be effective for us on October 1, 2013. We do not expect the adoption of these standards to have a material effect on our financial statements.

Comprehensive Income. In February 2013, the FASB issued ASU 2013-02, Comprehensive Income (Topic 220): Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income. This 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. ASU 2013-02 will be effective for us on October 1, 2013. We do not expect the adoption of this standard to have a material effect on our financial statements.

Income Taxes. In July 2013, the FASB issued 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. This standard amends the disclosure requirement of ASC Topic 740 by requiring an unrecognized tax benefit, or a portion of an unrecognized tax benefit be presented in the financial statements as a reduction to a deferred tax asset in most circumstances. ASU 2013-11 will be effective for us for the fiscal year beginning on October 1, 2014. We do not expect the adoption of this standard to have a material effect on our financial statements.

Regulated_Operations

Regulated Operations	12 Months Ended
Regulated Operations	Sep. 30, 2013
Regulated Operations [Abstract]	'
Public Utilities Disclosure	'
	Washington Gas accounts for its regulated operations in accordance with Financial Accounting Standards Board Accounting Standards Codification (ASC) Topic 980, Regulated Operations (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 recovery of costs that are expected to be incurred in the future (regulatory liabilities).
	At September 30, 2013 and 2012, 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,		2013		2012		2013		2012
	Current:
	Gas costs due from/to customers^(a)	$	-	$	16.9	$	23.4	$	11.1
	Interruptible sharing		10.7		0.4		1.9		2.1
	Provision for rate refunds		-		-		-		5.1
	Revenue normalization mechanisms for MD and VA		0.1		23.3		1.5		-
	Plant recovery mechanisms		-		0.1		0.2		2.4
	Other		-		0.1		-		-
	Total current	$	10.8	$	40.8	$	27	$	20.7
	Deferred:
	Accrued asset removal costs	$	-	$	-	$	321.3	$	325.6
	Deferred gas costs^(a)		94		-		-		19.5
	Pension and other post-retirement benefits
	Other post-retirement benefit costs—trackers^(b)		0.7		1.1		-		-
	Deferred pension costs/income—trackers^(b)		51		45.2		-		-
	ASC Topic 715 unrecognized costs/income^(a)(c)
	Pensions		155.1		289.6		-		-
	Other post-retirement benefits		34		99.2		-		-
	Total pension and other post-retirement benefits		240.8		435.1		-		-
	Other
	Income tax-related amounts due from/to customers^(d)		24.9		28.8		4.5		5
	Losses/gains on issuance and extinguishments of
	debt and interest-rate derivative instruments^(a)(e)		11.6		12.5		0.6		0.9
	Deferred gain on sale of assets^(a)		-		-		1.7		2
	Environmental response costs^(a)		0.6		4.4		-		-
	Rights-of-way fees		-		-		1.6		0.6
	Other costs—Business process outsourcing ^(a)		1.4		1.8		-		-
	Nonretirement postemployment benefits^(a)(f)		15.4		16.3		-		-
	Other regulatory expenses^(g)		11.9		4.6		5.1		6.5
	Total other	$	65.8	$	68.4	$	13.5	$	15
	Total deferred	$	400.6	$	503.5	$	334.8	$	360.1
	Total	$	411.4	$	544.3	$	361.8	$	380.8
	(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) The balance includes a $7.9 million asset related to the recoverable portion of the Chillum LNG facility.
	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, 2013 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
Accounts Payable and Other Accrued Liabilities	Sep. 30, 2013
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 Holdings and Washington Gas.

		WGL Holdings, Inc.
				September 30,
		(In millions)		2013		2012
		Accounts payable—trade	$	216.3	$	217
		Employee benefits and payroll accruals		23.4		20.3
		Embedded derivatives and other accrued liabilities		30.9		33.1
		Total	$	270.6	$	270.4

		Washington Gas Light Company
				September 30,
		(In millions)		2013		2012
		Accounts payable—trade	$	99.7	$	112.7
		Employee benefits and payroll accruals		21.4		18.2
		Embedded derivatives and other accrued liabilities		11.7		11.3
		Total	$	132.8	$	142.2

ShortTerm_Debt

Short-Term Debt	12 Months Ended
Short-Term Debt	Sep. 30, 2013
Short-Term Debt [Abstract]	'
Short-Term Debt	'
	NOTE 4. SHORT-TERM DEBT
	WGL Holdings 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 Holdings' 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, 2013 and 2012.
	Committed Credit Available (In millions)
	30-Sep-13	WGL Holdings ^(b)		Washington Gas		Total Consolidated
	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
	30-Sep-12
	Committed credit agreements
	Unsecured revolving credit facility, expires April 3, 2017^(a)	$	450	$	350	$	800
	Less: Commercial Paper		-148.9		-98.8		-247.7
	Net committed credit available	$	301.1	$	251.2	$	552.3

	(a)Both WGL Holdings and Washington Gas have the right to request extensions with the banks’ approval. WGL Holdings’ 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, 2013 and 2012, WGL Holdings had outstanding notes payable in the form of commercial paper of $373.1 million and $247.7 million, respectively, at a weighted average interest rate of 0.19% and 0.26%, respectively. At September 30, 2013 and 2012, Washington Gas had outstanding notes payable in the form of commercial paper of $124.5 million and $98.8 million, respectively, at a weighted average interest rate of 0.13% and 0.23%, respectively. At September 30, 2013 and 2012, there were no outstanding bank loans from WGL Holdings' or Washington Gas' revolving credit facilities.
	Depending on the type of borrowing option chosen under our revolving credit facilities, loans may bear interest at variable rates based on the Eurodollar rate, the higher of the prime lending rate or the Fed Funds effective rate, or at a competitive rate determined through auction. Facility fees for both companies are based on the long-term debt ratings of Washington Gas. If the long-term debt of Washington Gas were downgraded below certain levels, WGL Holdings and Washington Gas would be required to pay higher facility fees.
	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 Holdings 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 Holdings 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, 2013, WGL Holdings and Washington Gas were in compliance with all of the covenants under their revolving credit facilities.

LongTerm_Debt

Long-Term Debt	12 Months Ended
Long-Term Debt	Sep. 30, 2013
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, 2013 and 2012. Any FMBs that may be issued in the future will represent indebtedness of Washington Gas.
	SHELF REGISTRATION
	At September 30, 2013, Washington Gas had the capacity under a shelf registration to issue up to $450.0 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. There were no MTN or private placement issuances for the years ended September 30, 2013 and 2012. At September 30, 2013 and 2012, both outstanding MTNs and private placement notes were $583.0 million at a weighted average interest rate of 5.91%, respectively.
	The indenture for the unsecured MTNs and the note purchase agreement for the private placement notes provide that Washington Gas will not issue any FMBs under its Mortgage without securing all MTNs and the subject private placement notes with the Mortgage.
	Certain of Washington Gas' outstanding MTNs and private placement notes have a make-whole call feature that pays the holder a premium based on a spread over the yield to maturity of a U.S. Treasury security having a comparable maturity, when that particular note is called by Washington Gas before its stated maturity date. With the exception of this make-whole call feature, Washington Gas is not required to pay call premiums for calling debt prior to the stated maturity date.
	There were no MTN or private placement retirements for the year ended September 30, 2013. The table below shows MTN and private placement retirements for the year ended September 30, 2012.
		MTN and Private Placement Issuances and Retirements
		($ In millions)	Principal			Interest Rate		Nominal Maturity Date
		Year Ended September 30, 2012
		Retirements:
		10/17/11	$	7		6.05%		10/17/11
		10/19/11		15		6.00%		10/19/11
		10/19/11		5		6.00%		10/19/11
		2/27/12		25		6.00%		2/27/12
		6/19/12		25		5.90%		6/19/12
		Total	$	77
	LONG-TERM DEBT MATURITIES
	Maturities of long-term debt for each of the next five fiscal years and thereafter as of September 30, 2013 are summarized in the following table.
		Long-Term Debt Maturities^(a)
		(In millions)	MTNs		Other		Total
		2014	$	67	$	-	$	67
		2015		20		-		20
		2016		25		-		25
		2017		-		-		-⁺
		2018		-		-		-⁺
		Thereafter		471		-		471.0⁺
		Total (before project debt financing)	$	583	$	-	$	583
		Project debt financing^(b)		-		8.1		8.1⁺
		Total	$	583	$	8.1	$	591.1
		Less: current maturities		67		-		67
		Total non-current	$	516	$	8.1	$	524.1
		(a)Excludes unamortized discounts of $29,907 at September 30, 2013.
		(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, 2013
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]	'
Common Stock	'
	NOTE 6. COMMON STOCK — WGL HOLDINGS

	COMMON STOCK OUTSTANDING

	Shares of common stock outstanding were 51,774,204 and 51,611,647 at September 30, 2013 and 2012, respectively.

	COMMON STOCK RESERVES

	At September 30, 2013, there were 4,769,154 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)	1,054,437
	Dividend reinvestment and common stock purchase plan	2,963,895
	Employee savings plans	637,196
	Directors’ stock compensation plan	113,626
	Total common stock reserves	4,769,154
	(a)Effective March 1, 2007, WGL Holdings 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 295,973 shares dedicated to performance shares granted but not vested and include 26,372 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
Preferred Stock	Sep. 30, 2013
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
Earnings Per Share	Sep. 30, 2013
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, 2013, 2012 and 2011.
	Basic and Diluted EPS
		Years Ended September 30,
	(In thousands, except per share data)		2013		2012		2011
	Basic earnings per average common share:
	Net income applicable to common stock	$	80,253	$	139,818	$	117,050
	Average common shares outstanding—basic		51,697		51,522		51,195
	Basic earnings per average common share	$	1.55	$	2.71	$	2.29
	Diluted earnings per average common share:
	Net income applicable to common stock	$	80,253	$	139,818	$	117,050
	Average common shares outstanding—basic		51,697		51,522		51,195
	Stock-based compensation plans		111		67		100
	Total average common shares outstanding—diluted		51,808		51,589		51,295
	Diluted earnings per average common share	$	1.55	$	2.71	$	2.28

Income_Taxes

Income Taxes	12 Months Ended
Income Taxes	Sep. 30, 2013
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	NOTE 9. INCOME TAXES
	WGL Holdings files consolidated federal and District of Columbia returns and various state income tax returns. We are no longer subject to income tax examinations by the Internal Revenue Service for years before September 30, 2007. Substantially all state income tax years in major jurisdictions are closed for years before September 30, 2006.
	WGL Holdings 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 Holdings, are allocated to the subsidiaries that have taxable income. In fiscal year 2013, Washington Gas shared $1.3 million of tax benefits from the tax sharing agreement that was reflected as a tax decrease on Washington Gas' Statements of Income. For fiscal year 2012, Washington Gas realized tax savings of $0.3 million as a result of this tax sharing agreement, and for 2011, the tax effect of sharing was minimal. 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 returns for fiscal year ended September 30, 2012, we filed a combined unitary return for California, District of Columbia, Texas and West Virginia due to recent law changes.
	On March 23 and March 30, 2010 the Patient Protection and Affordable Care Act and the Health Care and Education Reconciliation Act, respectively (collectively “the PPACA”) became law resulting in comprehensive healthcare reform legislation that affect the accounting for employer provided benefits.
	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 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 PPACA became law and eliminated future Med D tax benefits for Washington Gas' tax years beginning after September 30, 2013. Washington Gas expects its future annual effective tax rate to increase over the pre-Healthcare reform rate by approximately 1%. Based on positions taken by the staff of 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 the Med D tax benefit. 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. On March 30, 2012, based on positions taken by the PSC of MD in Washington Gas' rate case during the fiscal year ended September 30, 2012, we determined that it was not probable that the PSC of MD would permit recovery of the asset either. Therefore, the Maryland portion of the regulatory asset related to the Med D benefit was charged to tax expense resulting in an increase in the effective tax rate for the fiscal year ended September 30, 2012. In June of 2013, the District of Columbia approved a five 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 19, 2013, the IRS issued final regulations regarding the tax treatment of amounts paid to acquire, produce or improve tangible property. These regulations are effective for WGL Holdings and Washington Gas for tax years beginning October 1, 2014, however, we do not expect them to have a material impact on the financial statements.
	The tables below provide the following for WGL Holdings 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, 2013 and 2012.
	WGL Holdings, Inc.
	Components of Income Tax Expense
		Years Ended September 30,
	(In thousands)		2013		2012		2011
	INCOME TAX EXPENSE
	Current:
	Federal	$	41,425	$	-13,188	$	18,531
	State		11,258		-30		10,899
	Total current		52,683		-13,218		29,430
	Deferred:
	Federal
	Accelerated depreciation		33,394		45,506		37,924
	Other		-31,173		44,727		12,067
	State
	Accelerated depreciation		6,795		9,412		6,689
	Other		-7,585		8,054		2,014
	Total deferred		1,431		107,699		58,694
	Amortization of investment tax credits		-1,822		-1,132		-974
	Total income tax expense	$	52,292	$	93,349	$	87,150
	WGL Holdings, Inc.
	Reconciliation Between the Statutory Federal Income Tax Rate and Effective Tax Rate
			Years Ended September 30,
	($ In thousands)		2013				2012				2011
	Income taxes at statutory federal income tax rate	$	46,853	35	%	$	82,070	35	%	$	71,932	35	%
	Increase (decrease) in income taxes resulting from:
	Accelerated depreciation less amount deferred		2,106	1.57			1,178	0.5			1,981	0.96
	Amortization of investment tax credits		-1,822	-1.36			-1,132	-0.48			-974	-0.47
	Cost of removal		-2,356	-1.76			-2,291	-0.98			-1,160	-0.56
	State income taxes-net of federal benefit		7,448	5.56			12,068	5.15			10,631	5.17
	Medicare Part D adjustment		-	-			2,827	1.21			4,714	2.29
	Other items-net		63	0.05			-1,371	-0.59			26	0.02
	Total income tax expense and effective tax rate	$	52,292	39.06	%	$	93,349	39.81	%	$	87,150	42.41	%
	WGL Holdings, Inc.
	Components of Deferred Income Tax Assets (Liabilities)
			September 30,
	(In thousands)		2013				2012
	ACCUMULATED DEFERRED INCOME TAXES	Current		Non-current		Current		Non-current
	Deferred income tax assets:
	Pensions	$	-	$	17,362	$	-	$	56,053
	Other post-retirement benefits		-		18,510		-		46,814
	Uncollectible accounts		8,127		-		7,891		-
	Inventory overheads		6,431		-		7,104		-
	Capital gains/losses-net		2		-		155		-
	Valuation allowance		-2		-		-155		-
	Employee compensation and benefits		5,876		37,301		5,355		26,145
	Customer advances		-		197		-		198
	Derivatives		-		7,872		-		-
	Deferred gas costs		4,911		-		-		-
	Other		816		4,161		810		1,172
	Total assets		26,161		85,403		21,160		130,382
	Deferred income tax liabilities:
	Accelerated depreciation and other plant related items		-		596,754		-		545,006
	Losses/gains on reacquired debt		-		1,567		-		1,758
	Income taxes recoverable through future rates		-		112,222		-		194,149
	Deferred gas costs		-		4,667		4,670		3,522
Derivatives		1,639		-		4,086		7,398
Total liabilities		1,639		715,210		8,756		751,833
Net accumulated deferred income tax assets (liabilities)	$	24,522	$	-629,807	$	12,404	$	-621,451
Washington Gas Light Company
Components of Income Tax Expense
			Years Ended September 30,
(In thousands)			2013		2012		2011
INCOME TAX EXPENSE
Current:
Federal		$	40,492	$	-13,155	$	9,415
State			7,515		-3,332		7,162
Total current			48,007		-16,487		16,577
Deferred:
Federal
Accelerated depreciation			34,518		45,661		37,363
Other			-35,982		27,851		-3,216
State
Accelerated depreciation			6,770		9,423		6,595
Other			-8,221		6,197		-640
Total deferred			-2,915		89,132		40,102
Amortization of investment tax credits			-895		-898		-893
Total income tax expense		$	44,197	$	71,747	$	55,786
Washington Gas Light Company
Reconciliation Between the Statutory Federal Income Tax Rate and Effective Tax Rate
		Years Ended September 30,
($ In thousands)		2013				2012				2011
Income taxes at statutory federal income tax rate	$	40,782	35	%	$	63,628	35	%	$	43,882	35	%
Increase (decrease) in income taxes resulting from:
Accelerated depreciation less amount deferred		2,106	1.81			1,178	0.65			1,981	1.58
Amortization of investment tax credits		-895	-0.77			-898	-0.49			-893	-0.71
Cost of removal		-2,356	-2.02			-2,291	-1.26			-1,160	-0.93
State income taxes-net of federal benefit		5,487	4.71			8,916	4.9			6,390	5.1
Consolidated tax sharing allocation		-1,290	-1.11			-309	-0.17			15	0.01
Medicare Part D adjustment		-	-			2,827	1.56			4,714	3.76
Other items-net		363	0.31			-1,304	-0.72			857	0.68
Total income tax expense and effective tax rate	$	44,197	37.93	%	$	71,747	39.47	%	$	55,786	44.49	%
Washington Gas Light Company
Components of Deferred Income Tax Assets (Liabilities)
		Years Ended September 30,
(In thousands)		2013				2012
ACCUMULATED DEFERRED INCOME TAXES	Current		Non-current		Current		Non-current
Deferred income tax assets:
Pensions	$	-	$	16,768	$	-	$	55,289
Other post-retirement benefits		-		18,474		-		46,502
Uncollectible accounts		6,948		-		6,823		-
Inventory overheads		6,431		-		7,105		-
Employee compensation and benefits		5,756		27,125		5,205		25,613
Customer advances		-		197		-		197
Derivatives		2,138		7,872		-		-
Deferred gas costs		4,911		-		-		-
Other		816		2,039		810		-
Total assets		27,000		72,475		19,943		127,601
Deferred income tax liabilities:
Accelerated depreciation and other plant related items		-		565,996		-		527,633
Losses/gains on reacquired debt		-		1,567		-		1,758
Income taxes recoverable through future rates		-		111,698		-		193,076
Deferred gas costs		-		4,667		4,670		3,521
Derivatives		-		-		857		7,399
Other		-		-		-		152
Total liabilities		-		683,928		5,527		733,539
Net accumulated deferred income tax assets (liabilities)	$	27,000	$	-611,453	$	14,416	$	-605,938
In June 2013, we filed our tax return for the year ended September 30, 2012.
The following table summarizes the change in unrecognized tax benefits during fiscal year 2013 and our total unrecognized tax benefits at September 30, 2013 under the provisions of ASC Topic 740, Income Taxes:
Unrecognized Tax Benefits
(In thousands)
Total unrecognized tax benefits, October 1, 2012	$	22,082
Increases in tax positions relating to current year		5,251
Decreases in tax positions relating to prior year		-2,282
Total unrecognized tax benefits, September 30, 2013	$	25,051

Unrecognized Tax Benefits
(In thousands)
Total unrecognized tax benefits, October 1, 2011	$	20,699
Increases in tax positions relating to current year		3,396
Decreases in tax positions relating to prior year		-2,013
Total unrecognized tax benefits, September 30, 2012	$	22,082
During the year, the unrecognized tax benefits for WGL Holdings and Washington Gas increased by approximately $3.0 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 Holdings' 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 Holdings 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, 2013, expense for interest on uncertain tax positions was minimal. During the fiscal year ended September 30, 2012, we reversed $1.6 million of interest previously accrued based on the completion of the IRS audit relating to the repairs project. During the fiscal year ended September 30, 2011, we accrued $0.7 million in expense for interest on uncertain tax positions.

Pension_and_Other_PostRetireme

Pension and Other Post-Retirement Benefit Plans	12 Months Ended
Pension and Other Post-Retirement Benefit Plans	Sep. 30, 2013
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. Employees hired on or after January 1, 2009 who are covered under collective bargaining agreements with the International Brotherhood of Teamsters Local 96 and the Office and Professional Employees International Union (“OPEIU”) Local 2 are not eligible to participate in the qualified pension plan. Employees hired on or after January 1, 2010 and covered under the collective bargaining agreement with the International Brotherhood of Electrical Workers Union (“IBEW”) Local 1900 are not eligible to participate in the qualified pension plan. Management employees hired on or after July 1, 2009 are not eligible to participate in the qualified pension plan. In addition, beginning January 1, 2010, 65 management employees elected to cease accruing additional benefits in the qualified pension plan. Their pension benefit is frozen based on the years of service accrued and salary as of December 31, 2009. However, their years of service continue to accrue for eligibility for early retirement.
	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.
	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 715-60, Compensation-Retirement Benefits—Defined Benefit Plans-Other Postretirement. 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 ending in 2013.
	Certain of our 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. Total matching contributions to the Washington Gas plan were $3.5 million, $3.4 million and $3.2 million during fiscal years 2013, 2012 and 2011, 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 $0.8 million and $0.6 million during fiscal years ended September 30, 2013 and 2012, respectively.
	Total matching contributions to the WGEServices plan were $0.8 million, $0.4 million and $0.4 million during fiscal years 2013, 2012 and 2011, respectively.
	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				Benefits
	Year Ended September 30,			2013		2012		2013		2012
	Change in projected benefit obligation
	Benefit obligation at beginning of year		$	937.2	$	787	$	480.1	$	502
	Service cost			17		12.9		9.6		8
	Interest cost			36.6		40.5		18.8		25.1
	Actuarial loss (gain)			-110		142.8		-62.3		-36.1
	Retiree contributions			-		-		4.6		3.9
	Benefits paid			-43.4		-46		-21		-22.8
	Projected benefit obligation at end of year		$	837.4	$	937.2	$	429.8	$	480.1
	Change in plan assets
	Fair value of plan assets at beginning of year		$	750.6	$	600	$	358.3	$	296.5
	Actual return on plan assets			38.6		117.1		19.9		57.7
	Company contributions			1.8		82		18		24.2
	Retiree contributions and Medicare Part D reimbursements			-		-		5.7		2.7
	Expenses			-2.4		-2.5		-		-
	Benefits paid			-43.4		-46		-21		-22.8
	Fair value of plan assets at end of year		$	745.2	$	750.6	$	380.9	$	358.3
	Funded status at end of year		$	-92.2	$	-186.6	$	-48.9	$	-121.8
	Total amounts recognized on balance sheet
	Current liability		$	-3.5	$	-3	$	-	$	-
	Accrued benefit liability			-88.7		-183.6		-48.9		-121.8
	Total recognized		$	-92.2	$	-186.6	$	-48.9	$	-121.8
	The projected benefit obligation (PBO) and accumulated benefit obligation (ABO) for the qualified pension plan was $788.7 million and $737.2 million, respectively, as of September 30, 2013, and $888.4 million and $819.9 million, respectively, at September 30, 2012. The PBO and ABO for the non-funded DB SERP was $47.8 million and $43.9 million, respectively, as of September 30, 2013, and $48.0 million and $40.6 million, respectively, as of September 30, 2012. The PBO and ABO for the non-funded DB Restoration were $0.8 million and $0.5 million, respectively, as of September 30, 2013 and $0.7 million and $0.3 million, respectively, as of September 30, 2012. The DB SERP and DB Restoration, included in pension benefits in the table above, have no assets.

	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, 2013 and 2012:
	Unrecognized Costs/Income Recorded on the Balance Sheet
	(In millions)				Pension Benefits				Health and Life Benefits
	September 30,			2013		2012		2013		2012
	Unrecognized actuarial net loss			$	171.1	$	304	$	55.3	$	128
	Unrecognized prior service cost (credit)				1.3		2.4		-22.4		-26.4
	Unrecognized transition obligation				-		-		-		1.1
	Total			$	172.4	$	306.4	$	32.9	$	102.7
	Regulatory asset			$	155.1	$	289.6	$	31.3	$	99.2
	Accumulated other comprehensive loss (pre-tax)^(a)				17.3		16.8		1.6		3.5
	Total			$	172.4	$	306.4	$	32.9	$	102.7
	(a)The total amount of accumulated other comprehensive loss recorded on our balance sheets at September 30, 2013 and 2012 is net of an income tax benefit of $7.9 million and $8.8 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 2013.
	Amounts Recognized During Fiscal Year 2013
		Regulatory assets/liabilities					Accumulated other comprehensive loss
	(In millions)	Pension Benefits		Health and Life Benefits			Pension Benefits		Health and Life Benefits
	Actuarial net loss	$	27.2	$	8.9		$	1.5	$	0.3
	Prior service cost (credit)		0.9		-3.8			0.1		-0.1
	Transition obligation		-		0.8			-		0.2
	Total	$	28.1	$	5.9		$	1.6	$	0.4
	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 2014.
	Amounts to be 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	$	-7.5		$	1.3	$	-0.3
	Prior service cost (credit)		0.2		3.2			0.1		0.1
Transition obligation		-		-			-		-
Total	$	15.7	$	-4.3		$	1.4	$	-0.2
The decrease in the actuarial net loss for pension benefits and health and life benefits to be recognized in fiscal year 2014 when compared to fiscal year 2013 is primarily due to an increase in the discount rate for our qualified pension and health and life plans.
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, 2013, 2012 and 2011 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,			2013		2012		2011		2013		2012		2011
Service cost		$	17	$	12.9	$	12.1	$	9.6	$	8	$	7.4
Interest cost			36.6		40.5		41.3		18.8		25.1		25.1
Expected return on plan assets			-41.9		-43.5		-44.6		-18.3		-18.8		-18.5
Recognized prior service cost			1		1		1.1		-3.9		-3.9		-3.9
Recognized actuarial loss			28.7		16.1		14.7		9.2		13.3		11.2
Amortization of transition obligation			-		-		-		1.1		1.1		1.1
Net periodic benefit cost			41.4		27		24.6		16.5		24.8		22.4
Amount allocated to construction projects			-5.7		-3.4		-2.9		-2.8		-3.7		-3.5
Amount deferred as regulatory asset (liability)-net			-3.7		-7.5		-7.1		2.4		1.5		2.1
Amount charged to expense		$	32	$	16.1	$	14.6	$	16.1	$	22.6	$	21
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.
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,			2013	2012		2013	2012
Discount rate^(a)			4.50%-5.00%	4.00%		5.10%	4.00%
Rate of compensation increase			3.85%-5.15%	3.85%-5.15%		3.85%	3.85%
(a)The increase in the discount rate in fiscal year 2013 compared to prior years primarily reflects the increase in long-term interest rates.
Net Periodic Benefit Cost Assumptions

	Pension Benefits				Health and Life Benefits
Years Ended September 30,	2013	2012	2011		2013	2012	2011
Discount rate^(a)	4.00%	5.30%	5.50%		4.00%	5.10%	5.75%
Expected long-term return on plan assets^(b)	6.75%	7.50%	7.50%		6.75%	7.40%	7.50%
Rate of compensation increase^(c)	3.85%-5.15%	3.85%-5.15%	3.25%		3.85%	3.85%-5.15%	3.25%
(a) The decrease in the discount rates over the last two fiscal years primarily reflects the decrease 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 Medicare and non-Medicare eligible retirees to be 7.5% for both fiscal years 2013 and 2012. Washington Gas expects these rates to decrease gradually to 5.0% in 2018 and remain at those levels thereafter.
Healthcare Trends
(In millions)	One Percentage-Point Increase				One Percentage-Point Decrease
Increase (decrease) total service and interest cost components	$	6.1			$	-4.6
Increase (decrease) post-retirement benefit obligation	$	61			$	-50.2
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, the 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.

For the qualified pension plan trust, the target asset allocations as of September 30, 2013 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 and Cash.

For healthcare and life insurance benefits for retired employees, Washington Gas' portion of the benefits is funded through two trusts: (i) the Washington Gas Light Company Postretirement Benefit Master Trust for Retired Previously Union-Eligible Employees and (ii) the Washington Gas Light Company Postretirement Benefit Master Trust for Retired Management Employees. The target asset allocations for the healthcare and life insurance benefit trust for retired union-eligible employees are 50% U.S. Large-Cap Equities and 50% Fixed Income and Cash for the union eligible trust and are 60% U.S. Large-Cap Equities and 40% Fixed Income and Cash 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.

Commingled funds make up the total portfolio of the healthcare and life insurance benefit trust for retired union-eligible employees. Commingled funds and separately managed portfolios are used for both the qualified pension plan and the healthcare and life insurance benefit trust for retired management employees.
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, 2013 and 2012:
	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	0
	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 Partnership^(e)			-		33.3		-		33.3	4.5
	Derivatives
		Futures Contracts^(f)		-		-0.3		-		-0.3	0
	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	%
Pension Plan Assets
										% of
($ In millions)		Level 1		Level 2		Level 3		Total		Total
At September 30, 2012
Cash and cash equivalents		$	0.8	$	-	$	-	$	0.8	0.1	%
Equity securities
	U.S. Small Cap		32		-		-		32	4.3
	Preferred Securities		-		0.1		-		0.1	-
Fixed income securities
	U.S. Treasuries		-		115.6		-		115.6	15.4
	U.S. Corporate Debt		-		84.2		-		84.2	11.2
	U.S. Agency Obligations and Government Sponsored Entities		-		20.1		-		20.1	2.7
	Asset-Backed Securities and Collateralized Mortgage Obligations		-		1.9		-		1.9	0.2
	Municipalities		-		9.4		-		9.4	1.2
	Non-U.S. Corporate Debt		-		11.7		-		11.7	1.6
	Repurchase Agreements^(a)		-		19.1		-		19.1	2.5
	Other^(b)		-		8.1		-		8.1	1.1
Mutual Funds^(c)			32.1		75.9		-		108	14.4
Commingled Funds and Pooled Separate Accounts^(d)			-		345.9		18.7		364.6	48.6
Derivatives
	Futures Contracts^(f)		-		-0.3		-		-0.3	-
Total fair value of plan investments		$	64.9	$	691.7	$	18.7	$	775.3	103.3	%
Receivable (payable)^(g)									-24.7	-3.3
Total plan assets at fair value								$	750.6	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, 2013 and September 30, 2012, investments in mutual funds consisted primarily of 70% corporate debt in the banking and finance, industrials, and utilities sectors and 30% equity securities of non-U.S. companies located in the countries comprising the Morgan Stanley Capital International EAFE Index, plus Canada.
(d)	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. At September 30, 2012, investments in commingled funds and pooled separate accounts consisted primarily of 71% common stock of large-cap U.S. companies; 11% short-term money market investments; 8% equity securities of non-U.S. companies; and 10% income producing properties located in the United States.
(e)	At September 30, 2013, investments in private equity/limited partnership consisted of common stock of international companies.
(f)	This category includes long-term U.S. Treasury interest rate futures contracts.
(g)	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, 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^(a)		-		4.6		-		4.6	1.2
	Others		-		5.3		-		5.3	1.4
Commingled Funds^(b)			-		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	%
At September 30, 2012
Cash and Cash Equivalents		$	0.3	$	-	$	-	$	0.3	0.1	%
Fixed Income Securities
	U.S Agency Obligations		-		4.6		-		4.6	1.3	%
	U.S. Treasuries		-		61.1		-		61.1	17.1
	U.S. Corporate Debt		-		60.7		-		60.7	17
	Municipalities		-		9.6		-		9.6	2.7
	Non-U.S. Corporate Debt		-		10.5		-		10.5	2.9
	Others		-		9.1		-		9.1	2.6
Commingled Funds^(b)			-		200.9		-		200.9	56.3
Total fair value of plan investments		$	0.3	$	356.5	$	-	$	356.8	100	%
Receivable (payable)									1.5	-
Total plan assets at fair value								$	358.3	100	%
(a)	This category primarily includes Yankee bonds and non-U.S. government bonds.
(b)	Investments in commingled funds consisted primarily of 66% common stock of large-cap U.S. companies and 34% U.S. agency obligations and government sponsored entities.
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 2013 and 2012:
	(In millions)
	Years Ended September 30,			2013			2012
	Balance, beginning of year			$	18.7		$	16.8
	Actual return on plan assets:
		Assets still held at year end			2.4			1.9
	Balance, end of year			$	21.1		$	18.7
Benefit Contribution
During fiscal year 2013, 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 2014, Washington Gas does not expect to make a contribution to its qualified pension plan and expects to make a payment of $3.5 million to its non-funded DB SERP. During fiscal year 2013, Washington Gas contributed $18.0 million to its health and life insurance benefit plans. Washington Gas expects to contribute $10.0 million to its health and life insurance benefit plans during fiscal year 2014.
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
	2014	$	48.4		$	18.7
	2015		49.6			19.7
	2016		50.4			20.8
	2017		51.9			21.8
	2018		53			22.7
	2019—2023		281.8			121.3
MEDICARE SUBSIDY RECEIPTS
As a sponsor of a retiree health care benefit plan that is at least actuarially equivalent to Medicare (Medicare Part D), Washington Gas is eligible to receive a federal subsidy under the Medicare Prescription Drug, Improvement and Modernization Act of 2003. All amounts received related to this subsidy are contributed by Washington Gas to its retiree healthcare plan. Washington Gas does not expect to receive amounts attributable to the Medicare subsidy in 2014
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.

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

The PSC of MD has not rendered a decision that specifically addresses recovery of post-retirement medical and life insurance benefit costs determined in accordance with GAAP. In Washington Gas' pending base rate case the Public Utility Law Judge issued a proposed order recommending that 50% of the expenses of the SERP allocable to Maryland not be recovered through rates. A final decision by the PSC of MD is expected on November 22, 2013. However, the PSC of MD has approved a level of rates sufficient to recover all other costs and pension costs as determined under GAAP.

Stock_Based_Compensation

Stock Based Compensation	12 Months Ended
Stock Based Compensation	Sep. 30, 2013
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 issued stock options and performance shares under our shareholder-approved 1999 Incentive Compensation Plan, as amended and restated (1999 Plan). The 1999 Plan allows WGL Holdings to issue up to 2,000,000 shares of common stock to persons, including officers and key employees, designated by the Human Resources Committee of the Board of Directors. Effective March 1, 2007, WGL Holdings adopted a shareholder-approved Omnibus Incentive Compensation Plan (Omnibus Plan). The Omnibus Plan was adopted to replace, on a prospective basis, the 1999 Plan. The Omnibus Plan provides similar benefits as provided under the 1999 Plan. Stock options, stock appreciation rights, restricted stock, deferred stock, stock granted 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 Holdings 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 Holdings for amounts remaining to be issued under these plans.
	During the fiscal year ended September 30, 2013, we granted performance shares and performance units under the Omnibus Plan; however, we did not issue any stock options. We have not issued stock options since October 2006. As of September 30, 2013, 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, we impose performance goals based on certain market conditions, which if unattained, may result in no performance shares or units being earned for the applicable performance period. These performance awards generally vest over three years from the date of grant. The actual number of performance shares and units that may be earned varies based on the total shareholder return of WGL Holdings relative to a selected peer group of companies over the three year performance period. Performance shares earned will be paid in shares of common stock of WGL Holdings. Performance units earned pursuant to terms of the grant will be paid in cash and are valued at $1.00 per performance unit. Our stock options generally have a vesting period of three years and expire ten years from the date of the grant. Performance units, performance shares and stock option awards provide for accelerated vesting upon a change in control of WGL Holdings. Additionally, 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, 2013, 2012 and 2011, we recognized stock-based compensation expense of $6.5 million, $3.6 million and $4.4 million, net of related income tax benefits of $2.6 million, $1.4 million and $1.8 million, respectively.
	As of September 30, 2013, total unrecognized compensation expense related to stock-based awards granted was $8.1 million. Performance shares and performance units comprised $3.8 million and $4.3 million of total unrecognized compensation expense, respectively. The total unrecognized compensation expense is expected to be recognized over a weighted average 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, 2013.
	Performance Share Activity
		Year Ended
		30-Sep-13
		Number of Shares^(a)		Weighted Average Grant-Date Fair Value
	Non-vested and outstanding, beginning of year	272,172		$	38.2
	Granted	109,665			39.73
	Vested	-			-
	Cancelled/forfeited	-85,864			34.37
	Non-vested and outstanding, end of year	295,973		$	39.88
	(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.
	There were no performance shares vested during the year ended September 30, 2013. The total intrinsic value of performance shares vested during the years ended 2012 and 2011 was $3.3 million and $4.6 million, respectively.

	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,	2013			2012			2011
	Expected stock-price volatility		19.4	%		27.8	%		29	%
	Dividend yield		3.98	%		3.97	%		4	%
	Weighted average grant-date fair value	$	39.73		$	38.99		$	41.14
	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, 2013.

	Performance Unit Activity
		Year Ended
		30-Sep-13
		Number of Units
	Non-vested and outstanding, beginning of year	10,034,413
	Granted	4,413,992
	Cancelled/forfeited	-2,865,849
	Non-vested and outstanding, end of year	11,582,556

	The total fair value of performance units outstanding at September 30, 2013 for the units expected to vest was $3.2 million. As of September 30, 2013, 2012 and 2011, we recorded a liability of $4.9 million, $2.1 million and $4.7 million, respectively, related to our performance units. The current and non-current portion of this liability is recorded in “Current Liabilities—other” and “Deferred Credits—other”, respectively. During fiscal year September 30, 2013, we did not make any cash payments to settle performance unit awards. During the fiscal years ended September 30, 2012 and 2011, we paid $2.8 million and $4.2 million in cash to settle performance unit awards, respectively.
	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-13
		10/1/2012 Grant	10/1/2011 Grant
	Expected stock-price volatility	17.80%	16.70%
	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, 2013.
	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, 2012	26,372			$	31.34	4.01	$	235
	Granted	-				-	-		-
	Exercised	-				-	-		-
	Cancelled/forfeited	-				-	-		-
	Outstanding at September 30, 2013	26,372			$	31.34	4.01	$	235
	Exercisable at September 30, 2013	26,372			$	31.34	4.01	$	235
	There were no stock options exercised during the year ended September 30, 2013 and no related tax benefits realized. We received $0.8 million and $4.1 million from the exercise of stock options during the years ended September 30, 2012 and 2011, respectively. The related tax benefits realized for the fiscal years ended September 30, 2012 and 2011 were $0.1 million and $0.4 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 16,600, 11,900 and 14,800 for the fiscal years ended September 30, 2013, 2012 and 2011, respectively. For those years, the weighted average fair value of the stock on the grant dates was $40.46, $44.30, and $36.74, 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 the year ended September 30, 2013, WGL Holdings recognized stock-based compensation expense related to these stock grants of $0.7 million, net of a related income tax benefits of $0.3 million. For each of the years ended September 30, 2012 and 2011, WGL Holdings recognized stock-based compensation expense related to these stock grants of $0.5 million, net of related income tax benefits of $0.2 million.

Environmental_Matters

Environmental Matters	12 Months Ended
Environmental Matters	Sep. 30, 2013
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 September 30, 2013 and 2012, Washington Gas recorded a liability of $8.5 million and $8.4 million, respectively, on an undiscounted basis related to future environmental response costs, which included the estimated costs for the ten 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, 2013 and 2012, Washington Gas estimated the maximum liability associated with all of its sites to be approximately $20.5 million and $17.3 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 September 30, 2013 and 2012, Washington Gas reported a regulatory asset of $0.6 million and $4.4 million, respectively, 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
Commitments and Contingencies	Sep. 30, 2013
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)
		2014	$	5.7
		2015		5.8
		2016		4.9
		2017		4
		2018		3.6
		Thereafter		1.8
		Total	$	25.8
	Rent expense totaled $5.6 million, $5.2 million and $5.0 million in fiscal years ended September 30, 2013, 2012 and 2011, respectively.

	REGULATED UTILITY OPERATIONS

	Natural Gas Contracts—Minimum Commitments

	At September 30, 2013, 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 2014 to 2029, 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 2014 to 2027. These agreements were entered into based on current estimates of growth of the Washington Gas system, together with other factors, such as current expectations of the timing and extent of unbundling initiatives in the Washington Gas service territory.

	The following table summarizes the minimum contractual payments that Washington Gas will make under its pipeline transportation, storage and peaking contracts during the next five fiscal years and thereafter.
		Washington Gas Contract Minimums
		(In millions)	Pipeline Contracts
		2014	$	187.9
		2015		197.1
		2016		226.9
		2017		220.8
		2018		213.1
		Thereafter		1,383.10
		Total	$	2,428.90
	Not included in the table above are short-term minimum commitments of $94.8 million to purchase natural gas in fiscal year 2014 at prices based on market conditions at the time the natural gas is purchased. These commitments relate to purchases of natural gas to serve utility customers. Additionally, excluded from the table above are purchases under our asset optimization program totaling 1,186.5 million therms from 2014-2028, which are partially offset by matching sales contracts of 96.9 million therms over that same period. Contracts under our asset optimization program are accounted for as derivatives (refer to Note 1—Accounting Policies for a description of our asset optimization program and Note 14—Derivative and Weather-Related Instruments for a discussion of our derivative instruments).
	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 Holdings 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.
	Maryland Jurisdiction
	Maryland Base Rate Case. On April 26, 2013, Washington Gas filed a request with the PSC of MD for a $30.8 million annual increase in revenues. The $30.8 million revenue increase requested in this application includes a proposed overall rate of return of 8.70% and a return on common equity of 10.70%. On May 31, 2013, Washington Gas revised the requested increase in revenues to $28.3 million. Among the proposals by Washington Gas are adjustments to amortize the effects of the change in the tax treatment of Medicare Part D and to amortize the costs to initiate the outsourcing agreement with Accenture LLP. These two items are also pending appeal of the last rate case decision.
	On October 10, 2013, the Public Utility Law Judge issued a Proposed Order recommending an $8.8 million increase in annual revenues based on an overall rate of return of 7.54% and a return on common equity of 9.25%. In addition, the Proposed Order recommended that Washington Gas be allowed to amortize the costs related to the change in tax treatment related to Medicare Part D and disallowed recovery of the costs to initiate the outsourcing agreement with Accenture LLP. The proposed order recommended the Washington Gas be allowed to recover the costs incurred related to the proposed Chillum liquefied natural gas facility, but did not recommend the unamortized balance be included in rate base. On October 24, 2013, the Washington Gas and other parties to the case filed appeal memoranda on the proposed order. Washington Gas requested the PSC of MD accept Washington Gas' proposed capital structure and approve a rate of return on equity of no less than 9.60%. Washington Gas also requested the PSC of MD approve the amortization the costs to achieve related to the outsourcing, to correct mathematical problems and clarify other issues in the case. On November 4, 2013 Washington Gas and other parties filed reply memoranda on appeal. A final order from the PSC of MD on Washington Gas' application is expected by November 22, 2013.
	Virginia Jurisdiction
	Affiliate Transactions. On June 16, 2011, Washington Gas submitted an application to the SCC of VA requesting approval of three affiliate transactions with WGL Midstream: (i) the transfer to WGL Midstream of the remainder of the term of two agreements for natural gas storage service at the Washington Storage Service ("WSS") and Eminence Storage Service ("ESS") storage fields; (ii) the sale to WGL Midstream of any storage gas balances associated with the WSS and ESS agreements and (iii) the assignment to WGL Midstream of Washington Gas' rights to buy base gas in the WSS storage field. Washington Gas proposed to make these affiliate transactions by September 30, 2011, coincident with the expiration of its PBR plan approved by the SCC of VA in a separate proceeding. On September 14, 2011, the SCC of VA issued an order denying Washington Gas' application to transfer Washington Gas' contracts for certain storage capacity resources to its affiliate, WGL Midstream. On October 4, 2011, Washington Gas filed a petition for reconsideration on this proceeding. On October 5, 2011, the SCC of VA granted Washington Gas' request that the matter be reconsidered.
	On August 30, 2013, Staff filed its response to the Company's petition. Staff argued that the transaction at debate in this proceeding is appropriately regulated by the Commission. On September 27, 2013, the Company filed its response to Staff's argument. The Senior Hearing Examiner's findings, issued in his October 31, 2013 report, was that the proposed transfer is not preempted by FERC and is subject to Commission jurisdiction under the Affiliates Act.
	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.
	The following table summarizes the contractual obligations and minimum commitments of WGL Midstream and WGEServices for both natural gas and electricity for the next five years and thereafter:
		Contract Minimums
		WGEServices						WGL Midstream
	(In millions)	Gas Purchase Commitments^(a)		Pipeline Contracts		Electric Purchase Commitments^(b)		Gas Purchase Commitments		Pipeline Contracts			Total
	2014	$	162.7	$	2.5	$	391.5	$	16.2	$	17	$	589.9
	2015		66.5		0.6		180.9		5.6		13		266.6
	2016		19.7		0.6		48.5		2.4		17.7		88.9
	2017		2.4		0.6		2.6		28.1		16.2		49.9
	2018		-		0.6		0.2		29		14.9		44.7
	Thereafter		-		1.8		-		397.5		121.3		520.6
	Total	$	251.3	$	6.7	$	623.7	$	478.8	$	200.1	$	1,560.60
	(a)Represents fixed price commitments with city gate equivalent deliveries.
	(b)Includes $7.2 million of commitments related to renewable energy credits.

	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, 2013 and 2012, work on these construction projects that was not completed or accepted by customers was valued at $6.7 million and $6.2 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, 2013 or September 30, 2012.

	Financial Guarantees

WGL Holdings 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, 2013, these guarantees totaled $305.4 million and $193.2 million for WGEServices and WGL Midstream, respectively. The amount of such guarantees is periodically adjusted to reflect changes in the level of financial exposure related to these purchase commitments. We also receive financial guarantees or other collateral from counterparties when required by our credit policy (refer to the section entitled “Credit Risk” for a further discussion of our credit policy). WGL Holdings also issued guarantees totaling $7.8 million at September 30, 2013 on behalf of certain of our non-utility subsidiaries and unconsolidated investments associated with their banking transactions. Of the total guarantees of $506.4 million, $6.0 million expired in October 2013. The remaining guarantees do not have specific maturity dates. For all of its financial guarantees, WGL Holdings may cancel any or all future obligations upon written notice to the counterparty, but WGL Holdings would continue to be responsible for the obligations created under the guarantees prior to the effective date of the cancellation.

Derivative_and_Weather_Related

Derivative and Weather Related Instruments	12 Months Ended
Derivative and Weather Related Instruments	Sep. 30, 2013
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 to lock-in operating margins that Washington Gas will ultimately realize. The derivatives used under this program are subject to mark-to-market accounting treatment.

	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 will ultimately realize from these transactions.

	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, 2013 was a loss of $33.2 million including an unrealized loss of $45.4 million. During the fiscal year ended September 30, 2012 we recorded a gain of $28.3 million including an unrealized gain of $15.9 million. During the fiscal year ended September 30, 2011 we recorded a gain of $1.9 million including an unrealized derivative loss of $13.2 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, which is typically over the life of the newly issued debt.

	Non-Utility Operations

	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. Washington Gas Resources has warrants to purchase stock from ASD Holdings, Inc., 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.

	Consolidated Operations

	Reflected in the tables below is information for WGL Holdings as well as Washington Gas. The information for WGL Holdings includes derivative instruments for both utility and non-utility operations.

	At September 30, 2013 and 2012, respectively, the absolute notional amounts of our derivatives are as follows:

	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 9/30/13.
		Absolute Notional Amounts
		of Open Positions on Derivative Instruments
		30-Sep-12		Notional Amounts
		Derivative transactions	WGL Holdings			Washington Gas
		Natural Gas (In millions of therms)
		Asset Optimization		4,798.50			3,039.10
		Retail sales		126.1			-
		Other risk-management activities		537.1			206.5
		Electricity (In millions of kWhs)
		Retail sales		5,080.50			-
		Other risk-management activities		16,898.00			-
		Warrants (In millions of shares)		4.4			-
	As of September 30, 2013, the increase in volume of asset optimization related derivatives is primarily the result of new long-term gas purchase contracts for Washington Gas and WGL Midstream.

	The following tables present the balance sheet classification for all derivative instruments as of September 30, 2013 and 2012.
	WGL Holdings, Inc.
	Balance Sheet Classification of Derivative Instruments
	(In millions)
	As of September 30, 2013	Derivative Assets		Derivative Liabilities		Netting of Collateral		Total
	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
As of September 30, 2012
Current Assets—Derivatives	$	80.4	$	-36.1	$	-1.1	$	43.2
Deferred Charges and Other Assets—Derivatives		103.9		-42.1		-		61.8
Accounts payable and other accrued liabilities		-0.2		-		-		-0.2
Current Liabilities—Derivatives		4.3		-40.8		-		-36.5
Deferred Credits—Derivatives		2.8		-18.6		2.6		-13.2
Total	$	191.2	$	-137.6	$	1.5	$	55.1
Washington Gas Light Company
Balance Sheet Classification of Derivative Instruments
(In millions)
As of September 30, 2013	Derivative Assets		Derivative Liabilities		Netting of Collateral		Total
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
As of September 30, 2012
Current Assets—Derivatives	$	20.7	$	-10.4	$	-1.1	$	9.2
Deferred Charges and Other Assets—Derivatives		92.8		-41.8		-		51
Current Liabilities—Derivatives		1.6		-12.1		-		-10.5
Deferred Credits—Derivatives		1.6		-5.1		-		-3.5
Total	$	116.7	$	-69.4	$	-1.1	$	46.2
The following tables present all gains and losses associated with derivative instruments for the years ended September 30, 2013, 2012 and 2011.
WGL Holdings, Inc. Gains and Losses on Derivative Instruments
(In millions)
Fiscal Year Ended September 30,		2013		2012		2011
Recorded to income
Operating revenues—non-utility	$	-9.9	$	19.2	$	-6.8
Utility cost of gas		-45.9		22.3		-9.4
Non-utility cost of energy-related sales		-2.4		-34.2		19.2
Other income-net		0.2		0.9		-
Recorded to regulatory assets
Gas costs		-115.1		42.2		-18.9
Other		-		-		6.2
Total	$	-173.1	$	50.4	$	-9.7
Washington Gas Gains and Losses on Derivative Instruments
(In millions)
Fiscal Year Ended September 30,		2013		2012		2011
Recorded to income
Utility cost of gas	$	-45.9	$	22.3	$	-9.4
Recorded to regulatory assets
Gas costs		-115.1		42.2		-18.9
Other		-		0		6.2
Total	$	-161	$	64.5	$	-22.1
Collateral
In accordance with ASC 815, WGL Holdings offsets the fair value of derivative instruments against the right to reclaim or obligation to return collateral for derivative instruments executed under the same master netting arrangement. 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. At September 30, 2012, Washington Gas, WGEServices and WGL Midstream posted $4.0 million, $8.2 million and $3.7 million, respectively, of collateral deposits with counterparties that were not offset against open and settled derivative contracts. In addition, at September 30, 2013 and 2012, Washington Gas held $4.6 million and $9.3 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 WGL Holdings 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, 2013, WGEServices posted $3.6 million of collateral related to its derivative liabilities that contained credit-related contingent features. At September 30, 2012, WGEServices posted $2.6 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, 2013 and 2012. 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, 2013 and 2012, respectively.


Potential Collateral Requirements for Derivative Liabilities
with Credit-risk-Contingent Features
(In millions)	WGL Holdings			Washington Gas
30-Sep-13
Derivative liabilities with credit-risk-contingent features	$	77		$	44.7
Maximum potential collateral requirements		33.6			1.7
30-Sep-12
Derivative liabilities with credit-risk-contingent features	$	101.2		$	60.8
Maximum potential collateral requirements		35.7			3.4
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 that reflect certain agreements with wholesale counterparties. Our credit policies are designed to mitigate this credit risk by requiring credit enhancements including, but not limited to, letters of credit, parent guarantees and cash collateral when deemed necessary. For certain counterparties or their guarantors that meet our specified creditworthiness criteria, Washington Gas, WGEServices and WGL Midstream grant unsecured credit, which we continuously monitor. Additionally, Washington Gas, WGEServices and WGL Midstream have separate agreements with wholesale counterparties that contain netting provisions to allow offsetting of the receivable and payable exposure related to each counterparty. At September 30, 2013, three counterparties each represented over 10% of Washington Gas' credit exposure to wholesale derivative counterparties for a total credit risk of $15.5 million; one counterparty represented over 10% of WGEServices' credit exposure to wholesale derivative counterparties for a total credit risk of $0.1 million; and three counterparties each represented over 10% of WGL Midstream's credit exposure to wholesale counterparties for a total credit risk of $7.2 million.

WEATHER-RELATED INSTRUMENTS

During the fiscal years ended September 30, 2013, 2012 and 2011, 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, 2012 and 2011, Washington Gas recorded a pre-tax net gain of $0.8 million and $7.9 million, and a pre-tax net loss of $2.8 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, 2013, 2012 and 2011, WGEServices recorded a pre-tax loss of $0.8 million, a pre-tax gain of $11.8 million and a pre-tax loss of $8.5 million, respectively, related to these instruments.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
Fair Value Measurements	Sep. 30, 2013
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 Holdings. 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, 2013 and 2012, 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 the WGL Holdings Chief Financial Officer. In accordance with WGL Holdings' 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, 2013 and 2012, Level 3 derivative assets and liabilities included: (i) physical contracts valued with significant basis adjustments to observable market data when delivery is to inactive market locations; (ii) long-dated positions where observable pricing is not available over the life of the contract; (iii) contracts valued using historical 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, 2013 and September 30, 2012, 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, 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
	At September 30, 2012
	Assets
	Natural gas related derivatives	$	-	$	85.9	$	80.7	$	166.6
	Electricity related derivatives		-		0.3		23.4		23.7
	Warrants		-		-		0.9		0.9
	Weather related instruments		-		-		1.5		1.5
	Total Assets	$	-	$	86.2	$	106.5	$	192.7
	Liabilities
	Natural gas related derivatives	$	-	$	-62.5	$	-41.1	$	-103.6
	Electricity related derivatives		-		-13.3		-20.6		-33.9
	Weather related instruments		-		-		-2		-2
	Total Liabilities	$	-	$	-75.8	$	-63.7	$	-139.5
	Washington Gas Light Company
	Fair Value Measurements Under the Fair Value Hierarchy
	(In millions)	Level 1		Level 2		Level 3		Total
	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
	At September 30, 2012
	Assets
	Natural gas related derivatives	$	-	$	41.4	$	75.3	$	116.7
	Weather related instruments		-		-		1.5		1.5
	Total Assets	$	-	$	41.4	$	76.8	$	118.2
	Liabilities
	Natural gas related derivatives	$	-	$	-29.7	$	-39.7	$	-69.4
	Weather related instruments		-		-		-2		-2
	Total Liabilities	$	-	$	-29.7	$	-41.7	$	-71.4
The following tables include 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, 2013 and September 30, 2012.


Quantitative Information about Level 3 Fair Value Measurements
(In millions)	Net Fair Value September 30, 2013	Valuation Techniques	Unobservable Inputs	Range
WGL Holdings
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
		Option Model	Annualized Volatility of Spot Market Natural Gas	34.6% -	276.60%
Electricity related derivatives	$2.40	Discounted Cash Flow	Electricity Congestion Price (per mega watt hour)	($1.995) -	$64.15
Washington Gas
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
		Option Model	Annualized Volatility of Spot Market Natural Gas	46.8% -	276.60%

Quantitative Information about Level 3 Fair Value Measurements
(In millions)	Net Fair Value September 30, 2012	Valuation Techniques	Unobservable Inputs	Range
WGL Holdings
Natural gas related derivatives	$39.60	Discounted Cash Flow	Natural Gas Basis Price (per dekatherm)	($0.250) -	$1.18

		Option Model	Natural Gas Basis Price (per dekatherm)	$0.050 -	$1.18
		Option Model	Annualized Volatility of Spot Market Natural Gas	37.80% -	236.03%
Electricity related derivatives	$2.80	Discounted Cash Flow	Electricity Congestion Price (per mega watt hour)	($2.204) -	$64.70
Washington Gas
Natural gas related derivatives	$35.60	Discounted Cash Flow	Natural Gas Basis Price (per dekatherm)	($0.250) -	$1.18

		Option Model	Natural Gas Basis Price (per dekatherm)	$0.090 -	$0.86
		Option Model	Annualized Volatility of Spot Market Natural Gas	37.80% -	236.03%
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, 2013 and 2012, respectively.


WGL Holdings 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


WGL Holdings 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, 2012
Balance at October 1, 2011	$	-3.9	$	-6.8	$	-1.4	$	-	$	-12.1
Realized and unrealized gains (losses)
Recorded to income		22.1		-47.7		7.9		0.9		-16.8
Recorded to regulatory assets - gas costs		25.7		-		-		-		25.7
Transfers out of Level 3		-1.6		-		-6.3		-		-7.9
Sales		-		-		-2.1		-		-2.1
Purchases		-		4.1		1.4		-		5.5
Settlements		-2.7		53.2		-		-		50.5
Balance at September 30, 2012	$	39.6	$	2.8	$	-0.5	$	0.9	$	42.8


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


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, 2012
Balance at October 1, 2011	$	-4.9	$	-	$	-1.4	$	-	$	-6.3
Realized and unrealized gains (losses)
Recorded to income		14.3		-		7.9		-		22.2
Recorded to regulatory assets - gas costs		25.7		-		-		-		25.7
Transfers out of Level 3		-0.3		-		-6.3		-		-6.6
Sales		-		-		-2.1		-		-2.1
Purchases		-		-		1.4		-		1.4
Settlements		0.8		-		-		-		0.8
Balance at September 30, 2012	$	35.6	$	-	$	-0.5	$	-	$	35.1

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 Holdings and Washington Gas net derivative assets transferred out of Level 3 during the fiscal year ended September 30, 2013 reflected an increase in 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, 2013, 2012 and 2011, related to fair value measurements using significant level 3 inputs.
WGL Holdings 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 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
WGL Holdings, Inc. Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements
(In millions)
Fiscal Year Ended September 30, 2011
Operating revenues—non-utility	$	-15.2
Utility cost of gas		-4.4
Non-utility cost of energy-related sales		15.8
Operation and maintenance expense		-3.4
Total	$	-7.2
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 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
Utility cost of gas	$	14.3	$	-	$	-	$	-	$	14.3
Operation and maintenance expense		-		-		7.9		-		7.9
Total	$	14.3	$	-	$	7.9	$	-	$	22.2
Washington Gas Light Company Realized and Unrealized Gains (Losses) Recorded for Level 3 Measurements
(In millions)
Fiscal Year Ended September 30, 2011
Utility cost of gas	$	-4.4
Operation and maintenance expense		-3.4
Total	$	-7.8
Unrealized gains (losses) for the fiscal years ended September 30, 2013, September 30, 2012 and September 30, 2011 attributable to derivative assets and liabilities measured using significant Level 3 inputs were recorded as follows, respectively:
WGL Holdings 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 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
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
WGL Holdings, Inc. Unrealized Gains (Losses) Recorded for Level 3 Measurements
(In millions)
Fiscal Year Ended September 30, 2011
Recorded to income
Operating revenues—non-utility	$	4
Utility cost of gas		-3.9
Non-utility cost of energy-related sales		2.9
Operation and maintenance expense		-0.7
Recorded to regulatory assets—gas costs		-11.4
Total	$	-9.1
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 Year 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
Washington Gas Light Company Unrealized Gains (Losses) Recorded for Level 3 Measurements
(In millions)
Fiscal Years Ended September 30, 2011
Recorded to income—Utility cost of gas	$	-3.9
Operation and maintenance expense		-0.7
Recorded to regulatory assets—gas costs		-11.4
Total	$	-16
The following table presents the carrying amounts and estimated fair values of our financial instruments at September 30, 2013 and 2012.
WGL Holdings Fair Value of Financial Instruments
At September 30,	2013				2012
(In millions)		Carrying Amount		Fair Value		Carrying Amount		Fair Value
Money market funds ^(a)	$	6.5	$	6.5	$	7.2	$	7.2
Other short- term investments^(a)	$	0.1	$	0.1	$	0.8	$	0.8
Commercial paper ^(b)	$	373.1	$	373.1	$	247.7	$	247.7
Long-term debt^(c)	$	524.1	$	630.2	$	589.2	$	758.9

Washington Gas Light Company Fair Value of Financial Instruments
At September 30,	2013				2012
(In millions)		Carrying Amount		Fair Value		Carrying Amount		Fair Value
Money market funds ^(a)	$	3.1	$	3.1	$	4.1	$	4.1
Other short- term investments^(a)	$	0.1	$	0.1	$	0.8	$	0.8
Commercial paper ^(b)	$	124.5	$	124.5	$	98.8	$	98.8
Long-term debt^(c)	$	524.1	$	630.2	$	589.2	$	758.9
(a)Balance located in cash and cash equivalents in the accompanying balance sheets.
(b)Balance is located in notes payable in the accompanying balance sheets.
(c)Excludes 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, 2013 and 2012 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, 2013, Washington Gas impaired its previous operations 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. During the fiscal year ended September 30, 2012, Washington Gas impaired this facility from a carrying amount of $29.9 million down to its fair value of $24.9 million, with an impairment charge of $5.0 million (refer to Note 1 -- Accounting Policies for a discussion of this impairment). The fair value of this facility is a level 3 measurement. The valuation of the facility was valued using the discounted cash value model that incorporates the anticipated sale proceeds as indicated through a comparable analysis, incorporating expected market trends, prepared by an independent consultant and the estimated costs to the carry the asset until a sale is completed.

Operating_Segment_Reporting

Operating Segment Reporting	12 Months Ended
Operating Segment Reporting	Sep. 30, 2013
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. Our four segments are summarized below.
	During fiscal year 2013, we made certain changes to our operating segments to reflect the recent growth of our non-utility business activities and the impact of those activities on our financial performance. All activities of WGSW are reported within the Commercial Energy Systems segment. WGSW had previously been reported within “Other Activities”. WGSW is a holding company formed to invest in alternative energy assets. As these operations align with those of the Commercial Energy Systems segment, and our chief operating decision maker reviews the operations of these units together, their combination for reporting purposes was deemed appropriate. Prior period operating segment information has been recast to conform to current period presentation. In the fourth quarter, we changed the segment name of Wholesale Energy Services to Midstream Energy Services to reflect changes in the nature of our wholesale business operations. In response to significant changes in market dynamics, our operations in this segment are now focused on the investment, acquisition and asset optimization of midstream infrastructure assets.


	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, 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 Holdings and Washington Gas Resources are included in this segment.

	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.

	The following tables present operating segment information for the fiscal years ended September 30, 2013, 2012 and 2011.
	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			242,819		49,574		6,875		8,683		9,344		-197		317,098
		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	$	1,047,727	$	1,226,373	$	34,046	$	9,281	$	9,441	$	-27,070	$	2,299,798
	Operating Income (Loss)				152,630		52,991		1,171		-29,671		-9,441		-1,340		166,340
	Equity in Earnings of Unconsolidated Affiliates				-		-		1,070		312		128		-		1,510
	Other Income (Expense)—Net				1,017		273		778		-		644		-686		2,026
	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	$	6,448	$	-	$	-	$	61,425
	(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 represents 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 and will expense them at that time.
	Operating Segment Financial Information
							Non-Utility Operations
	(In thousands)				Regulated Utility		Retail Energy-Marketing	Commercial Energy Systems		Midstream Energy Services		Other Activities		Eliminations		Consolidated
	Year Ended September 30, 2012
	Operating Revenues^(a)			$	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			226,852		52,161		5,414		2,860		3,660		-1,093		289,854
		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		50,821		4,071		280		240		16		-1		55,427
		Total Operating Expenses	$	920,948	$	1,201,905	$	58,112	$	3,216	$	3,676	$	-28,530	$	2,159,327
Operating Income (Loss)				216,718		65,165		2,213		-14,437		-3,676		-		265,983
Equity in Earnings of Unconsolidated Affiliates				-		-		947		-		293		-		1,240
Other Income (Expense)—Net				2,574		43		-32		-		1,145		-38		3,692
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.
Operating Segment Financial Information
						Non-Utility Operations
(In thousands)				Regulated Utility		Retail Energy-Marketing	Commercial Energy Systems		Midstream Energy Services		Other Activities		Eliminations		Consolidated
Year Ended September 30, 2011
Operating Revenues			$	1,288,539	$	1,443,156	$	39,190	$	4,574	$	-	$	-23,958	$	2,751,501
Operating Expenses:
	Cost of Energy-Related Sales			619,637		1,300,887		33,885		-		-		-23,958		1,930,451
	Operation			229,206		52,024		5,249		1,015		3,743		-		291,237
	Maintenance			48,292		-		-		-		-		-		48,292
	Depreciation and Amortization			90,289		650		351		35		-		-		91,325
	General Taxes and Other Assessments:
		Revenue Taxes		83,729		5,551		-		-		-		-		89,280
		Other		52,635		4,210		238		28		30		-		57,141
		Total Operating Expenses	$	1,123,788	$	1,363,322	$	39,723	$	1,078	$	3,773	$	-23,958	$	2,507,726
Operating Income (Loss)				164,751		79,834		-533		3,496		-3,773		-		243,775
Equity in Earnings of Unconsolidated Affiliates				-		-		-549		-		-		-		-549
Other Income—Net				2,577		28		15		-		306		-86		2,840
Interest Expense				40,462		53		-		-		117		-86		40,546
Dividends on Washington Gas Preferred Stock				1,320		-		-		-		-		-		1,320
Income Tax Expense (Benefit)				56,374		30,839		-543		1,313		-833		-		87,150
Net Income (Loss) Applicable to Common Stock			$	69,172	$	48,970	$	-524	$	2,183	$	-2,751	$	-	$	117,050
Total Assets at September 30, 2011			$	3,392,003	$	333,414	$	58,603	$	87,400	$	85,217	$	-147,603	$	3,809,034
Capital Expenditures			$	180,668	$	1,107	$	26,800	$	520	$	-	$	-	$	209,095
Equity Method Investments at September 30, 2011			$	-	$	-	$	7,551	$	-	$	-	$	-	$	7,551
(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.

Other_Investments

Other Investments	12 Months Ended
Other Investments	Sep. 30, 2013
Other Investments [Abstract]	'
Investment [Text Block]	'
	NOTE 17. OTHER INVESTMENTS
	Variable Interest Entities

	WGL Holdings assesses its contractual arrangements to determine control, and, by extension, correct classification of its investments. In most cases, control can be determined based on majority ownership or voting interests. However, there are certain entities known as variable interest entities (VIEs) for which control is difficult to discern based on ownership or voting interests alone. WGL Holdings and its subsidiaries first determine if an entity is a VIE. A VIE is an entity that does not have sufficient equity at risk to finance its activities without additional subordinated financial support from other parties, or whose equity investors, as a group, lack the characteristics of a controlling financial interest.

	At September 30, 2013, 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 EchoFirst Finance Company LLC (Echofirst) and Skyline Innovations, Inc (Skyline) for sale/leaseback arrangements for residential and commercial solar systems. WGSW is also a limited partner in ASD Solar LP, a partnership formed to own and operate a portfolio of residential solar projects, primarily rooftop photovoltaic power generation systems. As a limited partner, WGSW provides funding to the partnership but is excluded from involvement in the partnership's operations.

	At September 30, 2013, Washington Gas Resources owned 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.

	We have determined that we have a variable interest in four investments that qualify as VIEs. The four investments are:


	Echofirst,
	Skyline,
	ASD Solar LP, and
	Crab Run.


	An enterprise that has a controlling financial interest in a VIE is known as the VIE's primary beneficiary and is required to consolidate the VIE. A primary beneficiary has the obligation to absorb expected losses or the right to receive expected gains that could potentially be significant to the VIE and has decision-making rights associated with the activities that are most significant to the VIE's economic performance, including the power to design the VIE.

	In determining whether the Company is the primary beneficiary of a VIE, we assess which variable interest holder has control over the VIE's significant economic activities, such as the design of the companies, vendor selection, operation activities, construction, customer selection, and re-marketing activities after the termination of customer leases. For each of the VIEs identified above, it was determined that another entity controlled the economic activities and had the obligation to absorb expected losses or the right to receive expected gains that could be significant to the VIE. Our maximum financial exposure from 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. At September 30, 2013, we have determined that WGL Holdings and its subsidiaries are not the primary beneficiary for any of the above VIEs, therefore we have not consolidated any of the VIE entities.

	Skyline/Echofirst

	Our agreements with Skyline and Echofirst are accounted for as directing financing leases. WGSW records lease receipts and associated interest in the "Other Income" line in the accompanying Consolidated Statement of Income. WGSW held a $29.2 million and $3.4 million combined investment in direct financing leases at September 30, 2013 and 2012, respectively, of which $5.8 million and $0.7 million are current receivables recorded in "Other Current Assets" in the accompanying Consolidated Balance Sheets at September 30, 2013 and 2012, respectively.

	Minimum future lease payments receivable under direct financing leases over the next five years and thereafter are as follows:

		Minimum Payments Receivable for Direct Financing Leases
		(In millions)
		2014	$	5.8
		2015		1.2
		2016		1.2
		2017		1.2
		2018		1.2
		Thereafter		13.2
		Total	$	23.8

		Minimum payments receivable include $0.7 million of unearned income recognized as interest and exclude $5.4 million of residual values. The initial direct costs (incurred in FY 2012) associated with these investments was $0.7 million.
	ASD Solar, LP

	Our investment in ASD Solar, LP is accounted for under the equity method of accounting referred to as the hypothetical liquidation at book value method (HLBV) for allocating profits and losses; any profits and losses are included in “Earnings from Equity Method Investments” in the accompanying Consolidated Statement of Income and are added to or subtracted from the carrying amount of WGSW's investment balance.

	ASD Solar, LP is consolidated by the general partner, Solar Direct LLC. Solar Direct LLC is a wholly owned subsidiary of American Solar Direct Inc. (ASDI). The carrying amount of WGSW's investment in ASD Solar, LP exceeds the amount of the underlying equity in net assets by $30.4 million due to WGSW recording additions to its investment in ASD Solar, LP'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

	Crab Run is accounted for under the equity method of accounting; any profits and losses are included in “Earnings from Equity Method Investments” in the accompanying Consolidated Statement of Income and are added to or subtracted from the carrying amount of WGL Holdings' investment balance.

	Non-VIE Investments

	ASDHI

	Washington Gas Resources held a $5.6 million investment in American Solar Direct Holdings Inc. (ASDHI), at both September 30, 2013 and 2012. This investment is recorded at cost. The profits and losses are included in "Other Income" in the accompanying Consolidated Statement of Income. No identified events or changes in circumstances that many have a significant effect on the carrying value of this investment have occurred. At September 30, 2013 and 2012, Washington Gas Resources also held $1.1 million in warrants of ASDHI 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 $68 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 from the Marcellus region in northern Pennsylvania to major northeastern markets. Constitution is accounted for under the equity method of accounting; any profits and losses are included in “Earnings from Equity Method Investments” in the accompanying Consolidated Statement of Income and are added to or subtracted from the carrying amount of WGL Holdings' 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 and Income Statement location of the investments discussed in this footnote at September 30, 2013 and 2012 are as follows:

	As of September 30, 2013 *(in millions)*		VIEs		Non-VIEs		Total
	Assets
Non-Consolidated Investments	$	55.4	$	12.1	$	67.5
Direct financing leases receivable		23.4		-		23.4
Derivatives		-		1.1		1.1
Other		5.8		-		5.8
Total assets	$	84.6	$	13.2	$	97.8

Liabilities
Other	$	8.5	$	-	$	8.5
Total liabilities	$	8.5	$	-	$	8.5

Fiscal Year Ended September 30, 2013 *(in millions)*
Earnings from equity method investments	$	1	$	0.5	$	1.5
Depreciation expense		0.1		-		0.1
Other income		1.4		-		1.4
Net income	$	2.3	$	0.5	$	2.8

As of September 30, 2012 (in millions)
Assets
Non-Consolidated Investments	$	23.7	$	5.6	$	29.3
Direct financing leases receivable		2.7		-		2.7
Derivatives		-		0.9		0.9
Other		0.7		-		0.7
Total assets	$	27.1	$	6.5	$	33.6

Liabilities
Other	$	1	$	-	$	1
Total liabilities	$	1	$	-	$	1

Fiscal Year Ended September 30, 2012 (in millions)
Earnings from equity method investments	$	1.2	$	-	$	1.2
Other income		0.2		0.7		0.9
Net income	$	1.4	$	0.7	$	2.1

Related_Party_Transactions

Related Party - Transactions	12 Months Ended
Related Party - Transactions	Sep. 30, 2013
Related Party Transactions [Abstract]	'
Related Party Transactions Disclosure Text Block	'
	NOTE 18. RELATED PARTY TRANSACTIONS
	WGL Holdings 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 Holdings, 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 on Washington Gas' balance sheets for the fiscal years ended September 30, 2013 and 2012.
	Receivables / Payables from Associated Companies
	(In millions)	30-Sep-13			30-Sep-12
	Receivables from Associated Companies	$	7.2		$	5.5
	Payables to Associated Companies	$	20.6		$	28.5

	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 Holdings. 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)		2013		2012		2011
	Gas balancing service charge	$	25	$	26.8	$	24

	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 account payable from Washington Gas in the amount of $1.0 million and a receivable in the amount of $2.8 million at September 30, 2013 and 2012, respectively, related to an imbalance in gas volumes. Due to regulatory treatment, these receivables are not eliminated in the consolidated financial statements of WGL Holdings. Refer to Note 1—Accounting Policies for further discussion of these imbalance transactions.

	Washington Gas participates in a Purchase of Receivables (POR) program as approved by the Maryland Public Service Commission (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 Holdings. At September 30, 2013 and 2012, Washington Gas purchased $106.6 million and $95.7 million, respectively, of receivables from WGEServices.

Schedule_II

Schedule II	12 Months Ended
Schedule II	Sep. 30, 2013
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, 2013, 2012 and 2011
			Balance at		Additions Charged To						Balance
			Beginning		Costs and		Other				at End of
	(In thousands)		of Period		Expenses		Accounts^(a)		Deductions^(b)		Period
	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
	2011
	Valuation and Qualifying Accounts
	Deducted from Assets in the Balance Sheet:
	Allowance for Doubtful Accounts	$	20,306	$	18,455	$	3,761	$	24,553	$	17,969
	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, 2013, 2012 and 2011
			Balance at		Additions Charged To						Balance at
			Beginning		Costs and		Other				End of
	(In thousands)		of Period		Expenses		Accounts^(a)		Deductions^(b)		Period
	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
	2011
	Valuation and Qualifying Accounts
	Deducted from Assets in the Balance Sheet:
	Allowance for Doubtful Accounts	$	16,704	$	13,800	$	3,761	$	18,402	$	15,863
	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
Quarterly Financial Information	Sep. 30, 2013
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.
	Quarter Ended
	(In thousands, except per share data)	December 31			March 31		June 30	30-Sep
	Fiscal Year 2013
	WGL Holdings, Inc.
	Operating revenues	$	686,736	$	891,383	$	478,118	$	409,901
	Operating income (loss)	$	94,745	$	155,715	$	-8,981	$	-75,139
	Net income (loss) applicable to common stock	$	52,388	$	89,505	$	-10,015	$	-51,625
	Earnings (loss) per average share of common stock:
	Basic^(a)	$	1.01	$	1.73	$	-0.19	$	-1
	Diluted^(a)	$	1.01	$	1.73	$	-0.19	$	-1
	Washington Gas Light Company
	Operating revenues	$	355,817	$	535,950	$	180,882	$	127,708
	Operating income (loss)	$	72,167	$	134,490	$	-235	$	-55,289
	Net income (loss) applicable to common stock	$	38,387	$	76,935	$	-4,531	$	-39,789

	Fiscal Year 2012
	WGL Holdings, Inc.
	Operating revenues	$	727,757	$	839,444	$	438,326	$	419,783
	Operating income	$	93,925	$	138,411	$	20,533	$	13,114
	Net income applicable to common stock	$	50,438	$	74,179	$	7,457	$	7,744
	Earnings per average share of common stock:
	Basic^(a)	$	0.98	$	1.44	$	0.14	$	0.15
	Diluted^(a)	$	0.98	$	1.44	$	0.14	$	0.15

	Washington Gas Light Company
	Operating revenues	$	370,893	$	471,057	$	164,667	$	131,049
	Operating income (loss)	$	84,219	$	135,657	$	-2,691	$	-1,917
	Net income (loss) applicable to common stock	$	44,176	$	72,142	$	-6,061	$	-1,531
	(a)The sum of quarterly per share amounts may not equal annual per share amounts as quarterly calculations are based on varying numbers of common shares.
	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 the Chillum LNG storage facility. During the third quarter of fiscal year 2012, Washington Gas recorded an impairment charge of $5.0 million related to the Springfield Operations Center. Refer to Note 1—Accounting Policies of the Notes to Consolidated Financial Statements for further discussion of the impairment. During the fourth quarter of fiscal year 2012, Washington Gas recorded an adjustment of $2.8 million to reverse a regulatory asset that was established for future tax benefits related to Medicare Part D and one-time adjustments of $2.3 million and $0.5 million as a result of charges associated with regulatory proceedings.

Accounting_Policies_Policies

Accounting Policies (Policies)	12 Months Ended
Accounting Policies (Policies)	Sep. 30, 2013
Organization And Significant Accounting Policies [Abstract]	'
Consolidation, Policy [Policy Text Block]	'

	CONSOLIDATION OF FINANCIAL STATEMENTS
	The consolidated financial statements include the accounts of WGL Holdings 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.

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) is stated at original cost, including labor, materials, taxes and overhead costs incurred during the construction period. The cost of utility and other 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, 2013, 2012 and 2011 were 5.43%, 7.40% and 5.50%, respectively. Due to lower construction balances and significant decreases in short-term debt interest rates during fiscal year ended September 30, 2013, Washington Gas decreased capitalized AFUDC by $0.6 million. During fiscal year ended September 30, 2012, Washington Gas increased capitalized AFUDC by $0.7 million.
	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 2.86%, 2.87% and 2.84% during fiscal years 2013, 2012 and 2011, 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. Refer to Note 13—Commitments and Contingencies for a discussion of depreciation-related contingencies.
	At September 30, 2013 and 2012, 95.6% and 97.7%, respectively, of WGL Holdings' 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, 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.
	At September 30, 2013, Washington Gas recorded a $0.5 million impairment loss for the unrecoverable portion of the Chillum LNG storage facility. At September 30, 2013 and 2012, Washington Gas applied a discounted cash value model to the anticipated proceeds from a future sale of its Springfield Operations Center and recorded an impairment charge of $2.6 million and $5.0 million, respectively, in operation and maintenance expense.. Washington Gas is actively marketing the unused operations facility for sale.

Lease, Policy [Policy Text Block]	'
	OPERATING LEASES
	We have classified the lease of our corporate headquarters as an operating lease. We amortize to 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, 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 Holdings or our subsidiaries as of September 30, 2013 and 2012.

Revenue Recognition Accounting Policy, Gross and Net Revenue Disclosure [Policy Text Block]	'
	REVENUE AND COST RECOGNITION

	Regulated Utility Operations

	Revenues. For regulated deliveries of natural gas, Washington Gas reads meters and bills customers on a 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 on 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 delivered 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. The customer portion does not affect earnings.
	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.

	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.

	Commercial Energy Systems Segment. WGESystems recognizes income and expenses for all construction contracts using the percentage-of-completion method in “Operating Revenues—Non-utility” and “Non-Utility cost of energy-related sales.” Commercial Energy Systems also recognizes income from its solar assets based on the terms of the related power purchase agreements. WGSW recognizes income on its investments in solar 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 solar assets associated with the Skyline and EchoFirst associations.
	Midstream Energy Sevices 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 will recognize income on its investment using the cost approach of investment accounting.

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 years ended September 30, 2013, 2012 and 2011, WGL Holdings recorded a reduction of net income of $10.1 million, $22.4 million and $0.8 million, respectively, for lower-of-cost or market adjustment.
	In conjunction with optimizing Washington Gas' storage capacity, storage gas inventory may be subject to lower-of-cost or market adjustments. Washington Gas did not record any lower-of-cost or market adjustments related to its storage gas inventory for the fiscal year ended September 30, 2013. For the fiscal years ended 2012 and 2011, Washington Gas recorded a lower-of-cost or market adjustment related to its storage gas inventory, after the effects of regulatory sharing of $1.4 million and $0.3 million, respectively, which was recorded to “Utility cost of gas.”
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 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, 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 substantially to lock-in operating margins that Washington Gas will 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 will ultimately 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, Derivatives and Hedging. 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.

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, 2013 and 2012. 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 (ASC Topic 718) 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 asset retirement obligations (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.
New Accounting Pronouncements, Policy [Policy Text Block]	'
	ACCOUNTING STANDARDS ADOPTED IN FISCAL YEAR 2013
	Comprehensive Income. In June 2011, the FASB issued ASU 2011-05, Comprehensive Income (Topic 220): Presentation of Comprehensive Income. ASU 2011-05 intended to improve financial reporting by requiring companies to present items of net income in either one continuous statement, or in two separate but consecutive statements of net income and other comprehensive income. The new guidance removed the current presentation options in ASC Topic 220. The requirements of ASU 2011-05 did not change the components of comprehensive income that are recognized in net income or other comprehensive income, nor did the update change the computation of earnings per share (EPS). In December 2011, the FASB issued ASU 2011-12, Comprehensive Income (Topic 220): Deferral of the Effective Date for Amendments to the Presentation of Reclassifications of Items Out of Accumulated Other Comprehensive Income in Accounting Standards Update No. 2011-05. ASU 2011-12 indefinitely deferred the provisions requiring reclassification adjustments out of other comprehensive income (OCI) to be presented on the face of the financial statements. ASU 2011-05, as amended by ASU 2011-12, was effective for us on October 1, 2012. As a result of the standard, we presented comprehensive income in two separate but consecutive statements of net income and other comprehensive income. The adoption of this standard did not have a material effect on our financial statements.

	OTHER NEWLY ISSUED ACCOUNTING STANDARDS
	Balance Sheet Offsetting. In December 2011, the FASB issued ASU 2011-11, Disclosures about Offsetting Assets and Liabilities. This standard amends the disclosure requirements on offsetting in ASC Topic 210 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. In January 2013, the FASB issued ASU 2013-01, Clarifying the Scope of the Disclosures about Offsetting Assets and Liabilities. ASU 2013-01 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 2011-11 and ASU 2013-01 will be effective for us on October 1, 2013. We do not expect the adoption of these standards to have a material effect on our financial statements.

	Comprehensive Income. In February 2013, the FASB issued ASU 2013-02, Comprehensive Income (Topic 220): Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income. This 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. ASU 2013-02 will be effective for us on October 1, 2013. We do not expect the adoption of this standard to have a material effect on our financial statements.

	Income Taxes. In July 2013, the FASB issued 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. This standard amends the disclosure requirement of ASC Topic 740 by requiring an unrecognized tax benefit, or a portion of an unrecognized tax benefit be presented in the financial statements as a reduction to a deferred tax asset in most circumstances. ASU 2013-11 will be effective for us for the fiscal year beginning on October 1, 2014. We do not expect the adoption of this standard to have a material effect on our financial statements.
FairValueMeasurementPolicyPolicyTextBlock	'
	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 Holdings. 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]	'
	Our agreements with Skyline and Echofirst are accounted for as directing financing leases. WGSW records lease receipts and associated interest in the "Other Income" line in the accompanying Consolidated Statement of Income.
	Our investment in ASD Solar, LP is accounted for under the equity method of accounting referred to as the hypothetical liquidation at book value method (HLBV) for allocating profits and losses; any profits and losses are included in “Earnings from Equity Method Investments” 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 “Earnings from Equity Method Investments” in the accompanying Consolidated Statement of Income and are added to or subtracted from the carrying amount of WGL Holdings' investment balance.
	Washington Gas Resources held a $5.6 million investment in American Solar Direct Holdings Inc. (ASDHI), at both September 30, 2013 and 2012. This investment is recorded at cost. The profits and losses are included in "Other Income" in the accompanying Consolidated Statement of Income.
	Constitution is accounted for under the equity method of accounting; any profits and losses are included in “Earnings from Equity Method Investments” in the accompanying Consolidated Statement of Income and are added to or subtracted from the carrying amount of WGL Holdings' 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.

Accounting_Policies_Tables

Accounting Policies (Tables)	12 Months Ended
Accounting Policies (Tables)	Sep. 30, 2013
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,		2013			2012
	($ In millions)		Dollars	%		Dollars	%
	Regulated utility segment
	Distribution, transmission and storage	$	3,356.10	81.5	$	3,176.40	83.4
	General, miscellaneous and intangibles		430.6	10.4		428.3	11.3
	Construction work in progress (CWIP)		150.8	3.7		113.2	3
	Total regulated utility segment		3,937.50	95.6		3,717.90	97.7
	Unregulated segments		180.6	4.4		89.1	2.3
	Total	$	4,118.10	100	$	3,807.00	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)		2013		2012
		Asset retirement obligations at beginning of year	$	72.7	$	69.5
		Liabilities incurred in the period		1.2		1.9
		Liabilities settled in the period		-1		-1
		Accretion expense		3.3		3.3
		Revisions in estimated cash flows^(a)		27.8		-1
		Asset retirement obligations at the end of the year^(b)	$	104	$	72.7

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)		2013		2012
		Asset retirement obligations at beginning of year	$	71.5	$	68.3
		Liabilities incurred in the period		1.1		1.9
		Liabilities settled in the period		-1		-1
		Accretion expense		3.3		3.3
		Revisions in estimated cash flows^(a)		27.8		-1
		Asset retirement obligations at the end of the year^(b)	$	102.7	$	71.5
		(a) WGL revised its assumptions regarding the timing and amounts related to its obligation to cut, cap and purge pipeline. The revision is primarily driving by our accelerated pipeline replacement programs.
		(b) Includes short-term asset retirement obligations of $2.7 million and $1.3 million for fiscal year 2013 and 2012, respectively.

Regulated_Operations_Table

Regulated Operations (Table)	12 Months Ended
Regulated Operations (Table)	Sep. 30, 2013
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,		2013		2012		2013		2012
	Current:
	Gas costs due from/to customers^(a)	$	-	$	16.9	$	23.4	$	11.1
	Interruptible sharing		10.7		0.4		1.9		2.1
	Provision for rate refunds		-		-		-		5.1
	Revenue normalization mechanisms for MD and VA		0.1		23.3		1.5		-
	Plant recovery mechanisms		-		0.1		0.2		2.4
	Other		-		0.1		-		-
	Total current	$	10.8	$	40.8	$	27	$	20.7
	Deferred:
	Accrued asset removal costs	$	-	$	-	$	321.3	$	325.6
	Deferred gas costs^(a)		94		-		-		19.5
	Pension and other post-retirement benefits
	Other post-retirement benefit costs—trackers^(b)		0.7		1.1		-		-
	Deferred pension costs/income—trackers^(b)		51		45.2		-		-
	ASC Topic 715 unrecognized costs/income^(a)(c)
	Pensions		155.1		289.6		-		-
	Other post-retirement benefits		34		99.2		-		-
	Total pension and other post-retirement benefits		240.8		435.1		-		-
	Other
	Income tax-related amounts due from/to customers^(d)		24.9		28.8		4.5		5
	Losses/gains on issuance and extinguishments of
	debt and interest-rate derivative instruments^(a)(e)		11.6		12.5		0.6		0.9
	Deferred gain on sale of assets^(a)		-		-		1.7		2
	Environmental response costs^(a)		0.6		4.4		-		-
	Rights-of-way fees		-		-		1.6		0.6
	Other costs—Business process outsourcing ^(a)		1.4		1.8		-		-
	Nonretirement postemployment benefits^(a)(f)		15.4		16.3		-		-
	Other regulatory expenses^(g)		11.9		4.6		5.1		6.5
	Total other	$	65.8	$	68.4	$	13.5	$	15
	Total deferred	$	400.6	$	503.5	$	334.8	$	360.1
	Total	$	411.4	$	544.3	$	361.8	$	380.8
	(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) The balance includes a $7.9 million asset related to the recoverable portion of the Chillum LNG facility.

Accounts_Payable_and_Other_Acc1

Accounts Payable and Other Accrued Liabilities (Tables)	12 Months Ended
Accounts Payable and Other Accrued Liabilities (Tables)	Sep. 30, 2013
WGL Holdings, Inc.	'
Accounts Payable and Other Accrued Liabilities	'
		WGL Holdings, Inc.
				September 30,
		(In millions)		2013		2012
		Accounts payable—trade	$	216.3	$	217
		Employee benefits and payroll accruals		23.4		20.3
		Embedded derivatives and other accrued liabilities		30.9		33.1
		Total	$	270.6	$	270.4

Washington Gas Light Company	'
Accounts Payable and Other Accrued Liabilities	'
		Washington Gas Light Company
				September 30,
		(In millions)		2013		2012
		Accounts payable—trade	$	99.7	$	112.7
		Employee benefits and payroll accruals		21.4		18.2
		Embedded derivatives and other accrued liabilities		11.7		11.3
		Total	$	132.8	$	142.2

ShortTerm_Debt_Tables

Short-Term Debt (Tables)	12 Months Ended
Short-Term Debt (Tables)	Sep. 30, 2013
Short Term Debt Tables [Abstract]	'
Commited Credit Available	'
	Committed Credit Available (In millions)
	30-Sep-13	WGL Holdings ^(b)		Washington Gas		Total Consolidated
	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
	30-Sep-12
	Committed credit agreements
	Unsecured revolving credit facility, expires April 3, 2017^(a)	$	450	$	350	$	800
	Less: Commercial Paper		-148.9		-98.8		-247.7
	Net committed credit available	$	301.1	$	251.2	$	552.3

	(a)Both WGL Holdings and Washington Gas have the right to request extensions with the banks’ approval. WGL Holdings’ 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
Long Term Debt (Tables)	Sep. 30, 2013
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, 2012
		Retirements:
		10/17/11	$	7		6.05%		10/17/11
		10/19/11		15		6.00%		10/19/11
		10/19/11		5		6.00%		10/19/11
		2/27/12		25		6.00%		2/27/12
		6/19/12		25		5.90%		6/19/12
		Total	$	77
Long Term Debt Maturities	'
		Long-Term Debt Maturities^(a)
		(In millions)	MTNs		Other		Total
		2014	$	67	$	-	$	67
		2015		20		-		20
		2016		25		-		25
		2017		-		-		-⁺
		2018		-		-		-⁺
		Thereafter		471		-		471.0⁺
		Total (before project debt financing)	$	583	$	-	$	583
		Project debt financing^(b)		-		8.1		8.1⁺
		Total	$	583	$	8.1	$	591.1
		Less: current maturities		67		-		67
		Total non-current	$	516	$	8.1	$	524.1
		(a)Excludes unamortized discounts of $29,907 at September 30, 2013.
		(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
Derivative and Weather Related Instruments (Tables)	Sep. 30, 2013
Absolute Notional Amounts of Open Positions on Derivative Instruments	'
	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 9/30/13.
		Absolute Notional Amounts
		of Open Positions on Derivative Instruments
		30-Sep-12		Notional Amounts
		Derivative transactions	WGL Holdings			Washington Gas
		Natural Gas (In millions of therms)
		Asset Optimization		4,798.50			3,039.10
		Retail sales		126.1			-
		Other risk-management activities		537.1			206.5
		Electricity (In millions of kWhs)
		Retail sales		5,080.50			-
		Other risk-management activities		16,898.00			-
		Warrants (In millions of shares)		4.4			-
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			Washington Gas
	30-Sep-13
	Derivative liabilities with credit-risk-contingent features	$	77		$	44.7
	Maximum potential collateral requirements		33.6			1.7
	30-Sep-12
	Derivative liabilities with credit-risk-contingent features	$	101.2		$	60.8
	Maximum potential collateral requirements		35.7			3.4
WGL Holdings, Inc.	'
Balance Sheet Classification of Derivative Instruments	'
	WGL Holdings, Inc.
	Balance Sheet Classification of Derivative Instruments
	(In millions)
	As of September 30, 2013	Derivative Assets		Derivative Liabilities		Netting of Collateral		Total
	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
	As of September 30, 2012
	Current Assets—Derivatives	$	80.4	$	-36.1	$	-1.1	$	43.2
	Deferred Charges and Other Assets—Derivatives		103.9		-42.1		-		61.8
	Accounts payable and other accrued liabilities		-0.2		-		-		-0.2
	Current Liabilities—Derivatives		4.3		-40.8		-		-36.5
	Deferred Credits—Derivatives		2.8		-18.6		2.6		-13.2
	Total	$	191.2	$	-137.6	$	1.5	$	55.1
Gains and (Losses) on Derivative Instruments	'
	WGL Holdings, Inc. Gains and Losses on Derivative Instruments
	(In millions)
	Fiscal Year Ended September 30,		2013		2012		2011
	Recorded to income
	Operating revenues—non-utility	$	-9.9	$	19.2	$	-6.8
	Utility cost of gas		-45.9		22.3		-9.4
	Non-utility cost of energy-related sales		-2.4		-34.2		19.2
	Other income-net		0.2		0.9		-
	Recorded to regulatory assets
	Gas costs		-115.1		42.2		-18.9
	Other		-		-		6.2
	Total	$	-173.1	$	50.4	$	-9.7
Washington Gas Light Company	'
Balance Sheet Classification of Derivative Instruments	'
	Washington Gas Light Company
	Balance Sheet Classification of Derivative Instruments
	(In millions)
	As of September 30, 2013	Derivative Assets		Derivative Liabilities		Netting of Collateral		Total
	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
	As of September 30, 2012
	Current Assets—Derivatives	$	20.7	$	-10.4	$	-1.1	$	9.2
	Deferred Charges and Other Assets—Derivatives		92.8		-41.8		-		51
	Current Liabilities—Derivatives		1.6		-12.1		-		-10.5
	Deferred Credits—Derivatives		1.6		-5.1		-		-3.5
	Total	$	116.7	$	-69.4	$	-1.1	$	46.2
Gains and (Losses) on Derivative Instruments	'
	Washington Gas Gains and Losses on Derivative Instruments
	(In millions)
	Fiscal Year Ended September 30,		2013		2012		2011
	Recorded to income
	Utility cost of gas	$	-45.9	$	22.3	$	-9.4
	Recorded to regulatory assets
	Gas costs		-115.1		42.2		-18.9
	Other		-		0		6.2
	Total	$	-161	$	64.5	$	-22.1

Common_Stock_Tables

Common Stock (Tables)	12 Months Ended
	Sep. 30, 2013
Common Stock Tables [Abstract]	'
Common Stock Reserves	'
	Common Stock Reserves
	Reserve for:	Number of Shares
	Omnibus incentive compensation plan^(a)	1,054,437
	Dividend reinvestment and common stock purchase plan	2,963,895
	Employee savings plans	637,196
	Directors’ stock compensation plan	113,626
	Total common stock reserves	4,769,154
	(a)Effective March 1, 2007, WGL Holdings 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 295,973 shares dedicated to performance shares granted but not vested and include 26,372 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
Preferred Stock (Tables)	Sep. 30, 2013
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
Earnings Per Share (Tables)	Sep. 30, 2013
Earnings Per Share Tables [Abstract]	'
Earnings per Share	'
	Basic and Diluted EPS
		Years Ended September 30,
	(In thousands, except per share data)		2013		2012		2011
	Basic earnings per average common share:
	Net income applicable to common stock	$	80,253	$	139,818	$	117,050
	Average common shares outstanding—basic		51,697		51,522		51,195
	Basic earnings per average common share	$	1.55	$	2.71	$	2.29
	Diluted earnings per average common share:
	Net income applicable to common stock	$	80,253	$	139,818	$	117,050
	Average common shares outstanding—basic		51,697		51,522		51,195
	Stock-based compensation plans		111		67		100
	Total average common shares outstanding—diluted		51,808		51,589		51,295
	Diluted earnings per average common share	$	1.55	$	2.71	$	2.28

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
Income Taxes (Tables)	Sep. 30, 2013
Unrecognized Tax Benefits	'
	Unrecognized Tax Benefits
	(In thousands)
	Total unrecognized tax benefits, October 1, 2012	$	22,082
	Increases in tax positions relating to current year		5,251
	Decreases in tax positions relating to prior year		-2,282
	Total unrecognized tax benefits, September 30, 2013	$	25,051

	Unrecognized Tax Benefits
	(In thousands)
	Total unrecognized tax benefits, October 1, 2011	$	20,699
	Increases in tax positions relating to current year		3,396
	Decreases in tax positions relating to prior year		-2,013
	Total unrecognized tax benefits, September 30, 2012	$	22,082
WGL Holdings, Inc.	'
Components of Income Tax Expense	'
	WGL Holdings, Inc.
	Components of Income Tax Expense
		Years Ended September 30,
	(In thousands)		2013		2012		2011
	INCOME TAX EXPENSE
	Current:
	Federal	$	41,425	$	-13,188	$	18,531
	State		11,258		-30		10,899
	Total current		52,683		-13,218		29,430
	Deferred:
	Federal
	Accelerated depreciation		33,394		45,506		37,924
	Other		-31,173		44,727		12,067
	State
	Accelerated depreciation		6,795		9,412		6,689
	Other		-7,585		8,054		2,014
	Total deferred		1,431		107,699		58,694
	Amortization of investment tax credits		-1,822		-1,132		-974
	Total income tax expense	$	52,292	$	93,349	$	87,150
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)		2013				2012				2011
	Income taxes at statutory federal income tax rate	$	46,853	35	%	$	82,070	35	%	$	71,932	35	%
	Increase (decrease) in income taxes resulting from:
	Accelerated depreciation less amount deferred		2,106	1.57			1,178	0.5			1,981	0.96
	Amortization of investment tax credits		-1,822	-1.36			-1,132	-0.48			-974	-0.47
	Cost of removal		-2,356	-1.76			-2,291	-0.98			-1,160	-0.56
	State income taxes-net of federal benefit		7,448	5.56			12,068	5.15			10,631	5.17
	Medicare Part D adjustment		-	-			2,827	1.21			4,714	2.29
	Other items-net		63	0.05			-1,371	-0.59			26	0.02
	Total income tax expense and effective tax rate	$	52,292	39.06	%	$	93,349	39.81	%	$	87,150	42.41	%
Components of Deferred Income Tax Assets (Liabilities)	'
	WGL Holdings, Inc.
	Components of Deferred Income Tax Assets (Liabilities)
			September 30,
	(In thousands)		2013				2012
	ACCUMULATED DEFERRED INCOME TAXES	Current		Non-current		Current		Non-current
	Deferred income tax assets:
	Pensions	$	-	$	17,362	$	-	$	56,053
	Other post-retirement benefits		-		18,510		-		46,814
	Uncollectible accounts		8,127		-		7,891		-
	Inventory overheads		6,431		-		7,104		-
	Capital gains/losses-net		2		-		155		-
	Valuation allowance		-2		-		-155		-
	Employee compensation and benefits		5,876		37,301		5,355		26,145
	Customer advances		-		197		-		198
	Derivatives		-		7,872		-		-
	Deferred gas costs		4,911		-		-		-
	Other		816		4,161		810		1,172
	Total assets		26,161		85,403		21,160		130,382
	Deferred income tax liabilities:
	Accelerated depreciation and other plant related items		-		596,754		-		545,006
	Losses/gains on reacquired debt		-		1,567		-		1,758
	Income taxes recoverable through future rates		-		112,222		-		194,149
	Deferred gas costs		-		4,667		4,670		3,522
	Derivatives		1,639		-		4,086		7,398
	Total liabilities		1,639		715,210		8,756		751,833
	Net accumulated deferred income tax assets (liabilities)	$	24,522	$	-629,807	$	12,404	$	-621,451
Washington Gas Light Company	'
Components of Income Tax Expense	'
	Washington Gas Light Company
	Components of Income Tax Expense
				Years Ended September 30,
	(In thousands)			2013		2012		2011
	INCOME TAX EXPENSE
	Current:
	Federal		$	40,492	$	-13,155	$	9,415
	State			7,515		-3,332		7,162
	Total current			48,007		-16,487		16,577
	Deferred:
	Federal
	Accelerated depreciation			34,518		45,661		37,363
	Other			-35,982		27,851		-3,216
	State
	Accelerated depreciation			6,770		9,423		6,595
	Other			-8,221		6,197		-640
	Total deferred			-2,915		89,132		40,102
	Amortization of investment tax credits			-895		-898		-893
	Total income tax expense		$	44,197	$	71,747	$	55,786
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)		2013				2012				2011
	Income taxes at statutory federal income tax rate	$	40,782	35	%	$	63,628	35	%	$	43,882	35	%
	Increase (decrease) in income taxes resulting from:
	Accelerated depreciation less amount deferred		2,106	1.81			1,178	0.65			1,981	1.58
	Amortization of investment tax credits		-895	-0.77			-898	-0.49			-893	-0.71
	Cost of removal		-2,356	-2.02			-2,291	-1.26			-1,160	-0.93
	State income taxes-net of federal benefit		5,487	4.71			8,916	4.9			6,390	5.1
	Consolidated tax sharing allocation		-1,290	-1.11			-309	-0.17			15	0.01
	Medicare Part D adjustment		-	-			2,827	1.56			4,714	3.76
	Other items-net		363	0.31			-1,304	-0.72			857	0.68
	Total income tax expense and effective tax rate	$	44,197	37.93	%	$	71,747	39.47	%	$	55,786	44.49	%
Components of Deferred Income Tax Assets (Liabilities)	'
	Washington Gas Light Company
	Components of Deferred Income Tax Assets (Liabilities)
			Years Ended September 30,
	(In thousands)		2013				2012
	ACCUMULATED DEFERRED INCOME TAXES	Current		Non-current		Current		Non-current
	Deferred income tax assets:
	Pensions	$	-	$	16,768	$	-	$	55,289
	Other post-retirement benefits		-		18,474		-		46,502
	Uncollectible accounts		6,948		-		6,823		-
	Inventory overheads		6,431		-		7,105		-
	Employee compensation and benefits		5,756		27,125		5,205		25,613
	Customer advances		-		197		-		197
	Derivatives		2,138		7,872		-		-
	Deferred gas costs		4,911		-		-		-
	Other		816		2,039		810		-
	Total assets		27,000		72,475		19,943		127,601
	Deferred income tax liabilities:
	Accelerated depreciation and other plant related items		-		565,996		-		527,633
	Losses/gains on reacquired debt		-		1,567		-		1,758
	Income taxes recoverable through future rates		-		111,698		-		193,076
	Deferred gas costs		-		4,667		4,670		3,521
	Derivatives		-		-		857		7,399
	Other		-		-		-		152
	Total liabilities		-		683,928		5,527		733,539
	Net accumulated deferred income tax assets (liabilities)	$	27,000	$	-611,453	$	14,416	$	-605,938

Pension_and_Other_PostRetireme1

Pension and Other Post-Retirement Benefit Plans (Tables)	12 Months Ended
Pension and Other Post-Retirement Benefit Plans (Tables)	Sep. 30, 2013
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,			2013		2012		2011		2013		2012		2011
	Service cost		$	17	$	12.9	$	12.1	$	9.6	$	8	$	7.4
	Interest cost			36.6		40.5		41.3		18.8		25.1		25.1
	Expected return on plan assets			-41.9		-43.5		-44.6		-18.3		-18.8		-18.5
	Recognized prior service cost			1		1		1.1		-3.9		-3.9		-3.9
	Recognized actuarial loss			28.7		16.1		14.7		9.2		13.3		11.2
	Amortization of transition obligation			-		-		-		1.1		1.1		1.1
	Net periodic benefit cost			41.4		27		24.6		16.5		24.8		22.4
	Amount allocated to construction projects			-5.7		-3.4		-2.9		-2.8		-3.7		-3.5
	Amount deferred as regulatory asset (liability)-net			-3.7		-7.5		-7.1		2.4		1.5		2.1
	Amount charged to expense		$	32	$	16.1	$	14.6	$	16.1	$	22.6	$	21
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,			2013		2012		2013		2012
	Unrecognized actuarial net loss			$	171.1	$	304	$	55.3	$	128
	Unrecognized prior service cost (credit)				1.3		2.4		-22.4		-26.4
	Unrecognized transition obligation				-		-		-		1.1
	Total			$	172.4	$	306.4	$	32.9	$	102.7
	Regulatory asset			$	155.1	$	289.6	$	31.3	$	99.2
	Accumulated other comprehensive loss (pre-tax)^(a)				17.3		16.8		1.6		3.5
	Total			$	172.4	$	306.4	$	32.9	$	102.7
	(a)The total amount of accumulated other comprehensive loss recorded on our balance sheets at September 30, 2013 and 2012 is net of an income tax benefit of $7.9 million and $8.8 million, respectively.
Amount Recognized During Current Year [Table Text Block]	'
	Amounts Recognized During Fiscal Year 2013
		Regulatory assets/liabilities					Accumulated other comprehensive loss
	(In millions)	Pension Benefits		Health and Life Benefits			Pension Benefits		Health and Life Benefits
	Actuarial net loss	$	27.2	$	8.9		$	1.5	$	0.3
	Prior service cost (credit)		0.9		-3.8			0.1		-0.1
	Transition obligation		-		0.8			-		0.2
	Total	$	28.1	$	5.9		$	1.6	$	0.4
Post Retirement Benefits	'
	Post-Retirement Benefits
								Health and Life
	(In millions)			Pension Benefits				Benefits
	Year Ended September 30,			2013		2012		2013		2012
	Change in projected benefit obligation
	Benefit obligation at beginning of year		$	937.2	$	787	$	480.1	$	502
	Service cost			17		12.9		9.6		8
	Interest cost			36.6		40.5		18.8		25.1
	Actuarial loss (gain)			-110		142.8		-62.3		-36.1
	Retiree contributions			-		-		4.6		3.9
	Benefits paid			-43.4		-46		-21		-22.8
	Projected benefit obligation at end of year		$	837.4	$	937.2	$	429.8	$	480.1
	Change in plan assets
	Fair value of plan assets at beginning of year		$	750.6	$	600	$	358.3	$	296.5
	Actual return on plan assets			38.6		117.1		19.9		57.7
	Company contributions			1.8		82		18		24.2
	Retiree contributions and Medicare Part D reimbursements			-		-		5.7		2.7
	Expenses			-2.4		-2.5		-		-
	Benefits paid			-43.4		-46		-21		-22.8
	Fair value of plan assets at end of year		$	745.2	$	750.6	$	380.9	$	358.3
	Funded status at end of year		$	-92.2	$	-186.6	$	-48.9	$	-121.8
	Total amounts recognized on balance sheet
	Current liability		$	-3.5	$	-3	$	-	$	-
	Accrued benefit liability			-88.7		-183.6		-48.9		-121.8
	Total recognized		$	-92.2	$	-186.6	$	-48.9	$	-121.8
Amount Recognized During Next Fiscal Year	'
	Amounts to be 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	$	-7.5		$	1.3	$	-0.3
	Prior service cost (credit)		0.2		3.2			0.1		0.1
	Transition obligation		-		-			-		-
	Total	$	15.7	$	-4.3		$	1.4	$	-0.2
Benefit Obligations Assumptions/Net Periodic Benefits Assumptions	'
	Benefit Obligations Assumptions
				Pension Benefits			Health and Life Benefits
	September 30,			2013	2012		2013	2012
	Discount rate^(a)			4.50%-5.00%	4.00%		5.10%	4.00%
	Rate of compensation increase			3.85%-5.15%	3.85%-5.15%		3.85%	3.85%
	(a)The increase in the discount rate in fiscal year 2013 compared to prior years primarily reflects the increase in long-term interest rates.
	Net Periodic Benefit Cost Assumptions

		Pension Benefits				Health and Life Benefits
	Years Ended September 30,	2013	2012	2011		2013	2012	2011
	Discount rate^(a)	4.00%	5.30%	5.50%		4.00%	5.10%	5.75%
	Expected long-term return on plan assets^(b)	6.75%	7.50%	7.50%		6.75%	7.40%	7.50%
	Rate of compensation increase^(c)	3.85%-5.15%	3.85%-5.15%	3.25%		3.85%	3.85%-5.15%	3.25%
	(a) The decrease in the discount rates over the last two fiscal years primarily reflects the decrease 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	$	6.1			$	-4.6
	Increase (decrease) post-retirement benefit obligation	$	61			$	-50.2
Valuation Methods Level 3 assets	'
		(In millions)
		Years Ended September 30,			2013			2012
		Balance, beginning of year			$	18.7		$	16.8
		Actual return on plan assets:
			Assets still held at year end			2.4			1.9
		Balance, end of year			$	21.1		$	18.7
Expected Benefit Payments	'
		Expected Benefit Payments
		(In millions)	Pension Benefits			Health and Life Benefits
		2014	$	48.4		$	18.7
		2015		49.6			19.7
		2016		50.4			20.8
		2017		51.9			21.8
		2018		53			22.7
		2019—2023		281.8			121.3
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, 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	0
		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 Partnership^(e)			-		33.3		-		33.3	4.5
		Derivatives
			Futures Contracts^(f)		-		-0.3		-		-0.3	0
		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	%
	Pension Plan Assets
											% of
	($ In millions)		Level 1		Level 2		Level 3		Total		Total
	At September 30, 2012
	Cash and cash equivalents		$	0.8	$	-	$	-	$	0.8	0.1	%
	Equity securities
		U.S. Small Cap		32		-		-		32	4.3
		Preferred Securities		-		0.1		-		0.1	-
	Fixed income securities
		U.S. Treasuries		-		115.6		-		115.6	15.4
		U.S. Corporate Debt		-		84.2		-		84.2	11.2
		U.S. Agency Obligations and Government Sponsored Entities		-		20.1		-		20.1	2.7
		Asset-Backed Securities and Collateralized Mortgage Obligations		-		1.9		-		1.9	0.2
		Municipalities		-		9.4		-		9.4	1.2
		Non-U.S. Corporate Debt		-		11.7		-		11.7	1.6
		Repurchase Agreements^(a)		-		19.1		-		19.1	2.5
		Other^(b)		-		8.1		-		8.1	1.1
	Mutual Funds^(c)			32.1		75.9		-		108	14.4
	Commingled Funds and Pooled Separate Accounts^(d)			-		345.9		18.7		364.6	48.6
	Derivatives
		Futures Contracts^(f)		-		-0.3		-		-0.3	-
	Total fair value of plan investments		$	64.9	$	691.7	$	18.7	$	775.3	103.3	%
	Receivable (payable)^(g)									-24.7	-3.3
	Total plan assets at fair value								$	750.6	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, 2013 and September 30, 2012, investments in mutual funds consisted primarily of 70% corporate debt in the banking and finance, industrials, and utilities sectors and 30% equity securities of non-U.S. companies located in the countries comprising the Morgan Stanley Capital International EAFE Index, plus Canada.
	(d)	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. At September 30, 2012, investments in commingled funds and pooled separate accounts consisted primarily of 71% common stock of large-cap U.S. companies; 11% short-term money market investments; 8% equity securities of non-U.S. companies; and 10% income producing properties located in the United States.
	(e)	At September 30, 2013, investments in private equity/limited partnership consisted of common stock of international companies.
	(f)	This category includes long-term U.S. Treasury interest rate futures contracts.
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, 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^(a)		-		4.6		-		4.6	1.2
		Others		-		5.3		-		5.3	1.4
	Commingled Funds^(b)			-		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	%
	At September 30, 2012
	Cash and Cash Equivalents		$	0.3	$	-	$	-	$	0.3	0.1	%
	Fixed Income Securities
		U.S Agency Obligations		-		4.6		-		4.6	1.3	%
		U.S. Treasuries		-		61.1		-		61.1	17.1
		U.S. Corporate Debt		-		60.7		-		60.7	17
		Municipalities		-		9.6		-		9.6	2.7
		Non-U.S. Corporate Debt		-		10.5		-		10.5	2.9
		Others		-		9.1		-		9.1	2.6
	Commingled Funds^(b)			-		200.9		-		200.9	56.3
	Total fair value of plan investments		$	0.3	$	356.5	$	-	$	356.8	100	%
	Receivable (payable)									1.5	-
	Total plan assets at fair value								$	358.3	100	%
	(a)	This category primarily includes Yankee bonds and non-U.S. government bonds.
	(b)	Investments in commingled funds consisted primarily of 66% common stock of large-cap U.S. companies and 34% U.S. agency obligations and government sponsored entities.

Stock_Based_Compensation_Table

Stock Based Compensation (Tables)	12 Months Ended
Stock Based Compensation (Tables)	Sep. 30, 2013
Performance Share Activity	'
	Performance Share Activity
		Year Ended
		30-Sep-13
		Number of Shares^(a)		Weighted Average Grant-Date Fair Value
	Non-vested and outstanding, beginning of year	272,172		$	38.2
	Granted	109,665			39.73
	Vested	-			-
	Cancelled/forfeited	-85,864			34.37
	Non-vested and outstanding, end of year	295,973		$	39.88
	(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,	2013			2012			2011
	Expected stock-price volatility		19.4	%		27.8	%		29	%
	Dividend yield		3.98	%		3.97	%		4	%
	Weighted average grant-date fair value	$	39.73		$	38.99		$	41.14
Performance Unit Activity	'
	Performance Unit Activity
		Year Ended
		30-Sep-13
		Number of Units
	Non-vested and outstanding, beginning of year	10,034,413
	Granted	4,413,992
	Cancelled/forfeited	-2,865,849
	Non-vested and outstanding, end of year	11,582,556
Performance Units Fair Value Assumptions	'
	Fair Value Assumptions
		30-Sep-13
		10/1/2012 Grant	10/1/2011 Grant
	Expected stock-price volatility	17.80%	16.70%
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, 2012	26,372			$	31.34	4.01	$	235
	Granted	-				-	-		-
	Exercised	-				-	-		-
	Cancelled/forfeited	-				-	-		-
	Outstanding at September 30, 2013	26,372			$	31.34	4.01	$	235
	Exercisable at September 30, 2013	26,372			$	31.34	4.01	$	235

Committments_and_Contingencies

Committments and Contingencies (Tables)	12 Months Ended
Committments and Contingencies (Tables)	Sep. 30, 2013
Commitments and Contingencies [Line Items]	'
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	'
		Minimum Payments Under Operating Leases
		(In millions)
		2014	$	5.7
		2015		5.8
		2016		4.9
		2017		4
		2018		3.6
		Thereafter		1.8
		Total	$	25.8
Washington Gas Light Company	'
Commitments and Contingencies [Line Items]	'
Long-term Purchase Commitment [Table Text Block]	'
		Washington Gas Contract Minimums
		(In millions)	Pipeline Contracts
		2014	$	187.9
		2015		197.1
		2016		226.9
		2017		220.8
		2018		213.1
		Thereafter		1,383.10
		Total	$	2,428.90
Retail Energy Marketing [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		Electric Purchase Commitments^(b)		Gas Purchase Commitments		Pipeline Contracts			Total
	2014	$	162.7	$	2.5	$	391.5	$	16.2	$	17	$	589.9
	2015		66.5		0.6		180.9		5.6		13		266.6
	2016		19.7		0.6		48.5		2.4		17.7		88.9
	2017		2.4		0.6		2.6		28.1		16.2		49.9
	2018		-		0.6		0.2		29		14.9		44.7
	Thereafter		-		1.8		-		397.5		121.3		520.6
	Total	$	251.3	$	6.7	$	623.7	$	478.8	$	200.1	$	1,560.60
	(a)Represents fixed price commitments with city gate equivalent deliveries.
	(b)Includes $7.2 million of commitments related to renewable energy credits.

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
Fair Value Measurements (Tables)	Sep. 30, 2013
Quantitative Information about Level 3 Fair Value Measurements	'

	Quantitative Information about Level 3 Fair Value Measurements
	(In millions)	Net Fair Value September 30, 2013	Valuation Techniques	Unobservable Inputs	Range
	WGL Holdings
	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
			Option Model	Annualized Volatility of Spot Market Natural Gas	34.6% -	276.60%
	Electricity related derivatives	$2.40	Discounted Cash Flow	Electricity Congestion Price (per mega watt hour)	($1.995) -	$64.15
	Washington Gas
	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
			Option Model	Annualized Volatility of Spot Market Natural Gas	46.8% -	276.60%

	Quantitative Information about Level 3 Fair Value Measurements
	(In millions)	Net Fair Value September 30, 2012	Valuation Techniques	Unobservable Inputs	Range
	WGL Holdings
	Natural gas related derivatives	$39.60	Discounted Cash Flow	Natural Gas Basis Price (per dekatherm)	($0.250) -	$1.18

			Option Model	Natural Gas Basis Price (per dekatherm)	$0.050 -	$1.18
			Option Model	Annualized Volatility of Spot Market Natural Gas	37.80% -	236.03%
	Electricity related derivatives	$2.80	Discounted Cash Flow	Electricity Congestion Price (per mega watt hour)	($2.204) -	$64.70
	Washington Gas
	Natural gas related derivatives	$35.60	Discounted Cash Flow	Natural Gas Basis Price (per dekatherm)	($0.250) -	$1.18

			Option Model	Natural Gas Basis Price (per dekatherm)	$0.090 -	$0.86
			Option Model	Annualized Volatility of Spot Market Natural Gas	37.80% -	236.03%
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, 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
	At September 30, 2012
	Assets
	Natural gas related derivatives	$	-	$	85.9	$	80.7	$	166.6
	Electricity related derivatives		-		0.3		23.4		23.7
	Warrants		-		-		0.9		0.9
	Weather related instruments		-		-		1.5		1.5
	Total Assets	$	-	$	86.2	$	106.5	$	192.7
	Liabilities
	Natural gas related derivatives	$	-	$	-62.5	$	-41.1	$	-103.6
	Electricity related derivatives		-		-13.3		-20.6		-33.9
	Weather related instruments		-		-		-2		-2
	Total Liabilities	$	-	$	-75.8	$	-63.7	$	-139.5
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'

	WGL Holdings 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


	WGL Holdings 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, 2012
	Balance at October 1, 2011	$	-3.9	$	-6.8	$	-1.4	$	-	$	-12.1
	Realized and unrealized gains (losses)
	Recorded to income		22.1		-47.7		7.9		0.9		-16.8
	Recorded to regulatory assets - gas costs		25.7		-		-		-		25.7
	Transfers out of Level 3		-1.6		-		-6.3		-		-7.9
	Sales		-		-		-2.1		-		-2.1
	Purchases		-		4.1		1.4		-		5.5
	Settlements		-2.7		53.2		-		-		50.5
	Balance at September 30, 2012	$	39.6	$	2.8	$	-0.5	$	0.9	$	42.8

Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'
	WGL Holdings 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 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
	WGL Holdings, Inc. Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements
	(In millions)
	Fiscal Year Ended September 30, 2011
	Operating revenues—non-utility	$	-15.2
	Utility cost of gas		-4.4
	Non-utility cost of energy-related sales		15.8
	Operation and maintenance expense		-3.4
	Total	$	-7.2
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'
	WGL Holdings 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 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
	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
	WGL Holdings, Inc. Unrealized Gains (Losses) Recorded for Level 3 Measurements
	(In millions)
	Fiscal Year Ended September 30, 2011
	Recorded to income
	Operating revenues—non-utility	$	4
	Utility cost of gas		-3.9
	Non-utility cost of energy-related sales		2.9
	Operation and maintenance expense		-0.7
	Recorded to regulatory assets—gas costs		-11.4
	Total	$	-9.1
Fair Value of Financial Instruments	'
	WGL Holdings Fair Value of Financial Instruments
	At September 30,	2013				2012
	(In millions)		Carrying Amount		Fair Value		Carrying Amount		Fair Value
	Money market funds ^(a)	$	6.5	$	6.5	$	7.2	$	7.2
	Other short- term investments^(a)	$	0.1	$	0.1	$	0.8	$	0.8
	Commercial paper ^(b)	$	373.1	$	373.1	$	247.7	$	247.7
	Long-term debt^(c)	$	524.1	$	630.2	$	589.2	$	758.9

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, 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
	At September 30, 2012
	Assets
	Natural gas related derivatives	$	-	$	41.4	$	75.3	$	116.7
	Weather related instruments		-		-		1.5		1.5
	Total Assets	$	-	$	41.4	$	76.8	$	118.2
	Liabilities
	Natural gas related derivatives	$	-	$	-29.7	$	-39.7	$	-69.4
	Weather related instruments		-		-		-2		-2
	Total Liabilities	$	-	$	-29.7	$	-41.7	$	-71.4
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, 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


	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, 2012
	Balance at October 1, 2011	$	-4.9	$	-	$	-1.4	$	-	$	-6.3
	Realized and unrealized gains (losses)
	Recorded to income		14.3		-		7.9		-		22.2
	Recorded to regulatory assets - gas costs		25.7		-		-		-		25.7
	Transfers out of Level 3		-0.3		-		-6.3		-		-6.6
	Sales		-		-		-2.1		-		-2.1
	Purchases		-		-		1.4		-		1.4
	Settlements		0.8		-		-		-		0.8
	Balance at September 30, 2012	$	35.6	$	-	$	-0.5	$	-	$	35.1

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, 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 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
	Utility cost of gas	$	14.3	$	-	$	-	$	-	$	14.3
	Operation and maintenance expense		-		-		7.9		-		7.9
	Total	$	14.3	$	-	$	7.9	$	-	$	22.2
	Washington Gas Light Company Realized and Unrealized Gains (Losses) Recorded for Level 3 Measurements
	(In millions)
	Fiscal Year Ended September 30, 2011
	Utility cost of gas	$	-4.4
	Operation and maintenance expense		-3.4
	Total	$	-7.8
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, 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 Year 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
	Washington Gas Light Company Unrealized Gains (Losses) Recorded for Level 3 Measurements
	(In millions)
	Fiscal Years Ended September 30, 2011
	Recorded to income—Utility cost of gas	$	-3.9
	Operation and maintenance expense		-0.7
	Recorded to regulatory assets—gas costs		-11.4
	Total	$	-16
Fair Value of Financial Instruments	'
	Washington Gas Light Company Fair Value of Financial Instruments
	At September 30,	2013				2012
	(In millions)		Carrying Amount		Fair Value		Carrying Amount		Fair Value
	Money market funds ^(a)	$	3.1	$	3.1	$	4.1	$	4.1
	Other short- term investments^(a)	$	0.1	$	0.1	$	0.8	$	0.8
	Commercial paper ^(b)	$	124.5	$	124.5	$	98.8	$	98.8
	Long-term debt^(c)	$	524.1	$	630.2	$	589.2	$	758.9
	(a)Balance located in cash and cash equivalents in the accompanying balance sheets.
	(b)Balance is located in notes payable in the accompanying balance sheets.
	(c)Excludes current maturities and unamortized discounts.

Operating_Segment_Reporting_Ta

Operating Segment Reporting (Tables)	12 Months Ended
Operating Segment Reporting (Tables)	Sep. 30, 2013
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, 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			242,819		49,574		6,875		8,683		9,344		-197		317,098
		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	$	1,047,727	$	1,226,373	$	34,046	$	9,281	$	9,441	$	-27,070	$	2,299,798
	Operating Income (Loss)				152,630		52,991		1,171		-29,671		-9,441		-1,340		166,340
	Equity in Earnings of Unconsolidated Affiliates				-		-		1,070		312		128		-		1,510
	Other Income (Expense)—Net				1,017		273		778		-		644		-686		2,026
	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	$	6,448	$	-	$	-	$	61,425
	(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 represents 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 and will expense them at that time.
	Operating Segment Financial Information
							Non-Utility Operations
	(In thousands)				Regulated Utility		Retail Energy-Marketing	Commercial Energy Systems		Midstream Energy Services		Other Activities		Eliminations		Consolidated
	Year Ended September 30, 2012
	Operating Revenues^(a)			$	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			226,852		52,161		5,414		2,860		3,660		-1,093		289,854
		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		50,821		4,071		280		240		16		-1		55,427
			Total Operating Expenses	$	920,948	$	1,201,905	$	58,112	$	3,216	$	3,676	$	-28,530	$	2,159,327
	Operating Income (Loss)				216,718		65,165		2,213		-14,437		-3,676		-		265,983
	Equity in Earnings of Unconsolidated Affiliates				-		-		947		-		293		-		1,240
	Other Income (Expense)—Net				2,574		43		-32		-		1,145		-38		3,692
	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.
	Operating Segment Financial Information
							Non-Utility Operations
	(In thousands)				Regulated Utility		Retail Energy-Marketing	Commercial Energy Systems		Midstream Energy Services		Other Activities		Eliminations		Consolidated
	Year Ended September 30, 2011
	Operating Revenues			$	1,288,539	$	1,443,156	$	39,190	$	4,574	$	-	$	-23,958	$	2,751,501
	Operating Expenses:
		Cost of Energy-Related Sales			619,637		1,300,887		33,885		-		-		-23,958		1,930,451
		Operation			229,206		52,024		5,249		1,015		3,743		-		291,237
		Maintenance			48,292		-		-		-		-		-		48,292
		Depreciation and Amortization			90,289		650		351		35		-		-		91,325
		General Taxes and Other Assessments:
			Revenue Taxes		83,729		5,551		-		-		-		-		89,280
		Other		52,635		4,210		238		28		30		-		57,141
		Total Operating Expenses	$	1,123,788	$	1,363,322	$	39,723	$	1,078	$	3,773	$	-23,958	$	2,507,726
Operating Income (Loss)				164,751		79,834		-533		3,496		-3,773		-		243,775
Equity in Earnings of Unconsolidated Affiliates				-		-		-549		-		-		-		-549
Other Income—Net				2,577		28		15		-		306		-86		2,840
Interest Expense				40,462		53		-		-		117		-86		40,546
Dividends on Washington Gas Preferred Stock				1,320		-		-		-		-		-		1,320
Income Tax Expense (Benefit)				56,374		30,839		-543		1,313		-833		-		87,150
Net Income (Loss) Applicable to Common Stock			$	69,172	$	48,970	$	-524	$	2,183	$	-2,751	$	-	$	117,050
Total Assets at September 30, 2011			$	3,392,003	$	333,414	$	58,603	$	87,400	$	85,217	$	-147,603	$	3,809,034
Capital Expenditures			$	180,668	$	1,107	$	26,800	$	520	$	-	$	-	$	209,095
Equity Method Investments at September 30, 2011			$	-	$	-	$	7,551	$	-	$	-	$	-	$	7,551
(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.

Other_Investment_Tables

Other Investment (Tables)	12 Months Ended
Other Investment (Tables)	Sep. 30, 2013
Other Investments [Abstract]	'
Minimum Payments Receivable for Direct Financing Leases	'
		Minimum Payments Receivable for Direct Financing Leases
		(In millions)
		2014	$	5.8
		2015		1.2
		2016		1.2
		2017		1.2
		2018		1.2
		Thereafter		13.2
		Total	$	23.8
Location of Investments	'

	As of September 30, 2013 *(in millions)*		VIEs		Non-VIEs		Total
	Assets
	Non-Consolidated Investments	$	55.4	$	12.1	$	67.5
	Direct financing leases receivable		23.4		-		23.4
	Derivatives		-		1.1		1.1
	Other		5.8		-		5.8
	Total assets	$	84.6	$	13.2	$	97.8

	Liabilities
	Other	$	8.5	$	-	$	8.5
	Total liabilities	$	8.5	$	-	$	8.5

	Fiscal Year Ended September 30, 2013 *(in millions)*
	Earnings from equity method investments	$	1	$	0.5	$	1.5
	Depreciation expense		0.1		-		0.1
	Other income		1.4		-		1.4
	Net income	$	2.3	$	0.5	$	2.8

	As of September 30, 2012 (in millions)
	Assets
	Non-Consolidated Investments	$	23.7	$	5.6	$	29.3
	Direct financing leases receivable		2.7		-		2.7
	Derivatives		-		0.9		0.9
	Other		0.7		-		0.7
	Total assets	$	27.1	$	6.5	$	33.6

	Liabilities
	Other	$	1	$	-	$	1
	Total liabilities	$	1	$	-	$	1

	Fiscal Year Ended September 30, 2012 (in millions)
	Earnings from equity method investments	$	1.2	$	-	$	1.2
	Other income		0.2		0.7		0.9
	Net income	$	1.4	$	0.7	$	2.1

Related_Party_Transactions_Tab

Related Party Transactions (Tables)	12 Months Ended
Related Party Transactions (Tables)	Sep. 30, 2013
Related Party Transactions [Abstract]	'
Receivables and Payables from Associated Companies	'
	Receivables / Payables from Associated Companies
	(In millions)	30-Sep-13			30-Sep-12
	Receivables from Associated Companies	$	7.2		$	5.5
	Payables to Associated Companies	$	20.6		$	28.5

	Washington Gas - Gas Balancing Service Charges
			Years Ended
			September 30,
	(In millions)		2013		2012		2011
	Gas balancing service charge	$	25	$	26.8	$	24

Quarterly_Financial_Informatio1

Quarterly Financial Information (Tables)	12 Months Ended
Quarterly Financial Information (Tables)	Sep. 30, 2013
Quarterly Financial Information Disclosure [Abstract]	'
Schedule Of Quarterly Financial Information [Table Text Block]	'
	Quarter Ended
	(In thousands, except per share data)	December 31			March 31		June 30	30-Sep
	Fiscal Year 2013
	WGL Holdings, Inc.
	Operating revenues	$	686,736	$	891,383	$	478,118	$	409,901
	Operating income (loss)	$	94,745	$	155,715	$	-8,981	$	-75,139
	Net income (loss) applicable to common stock	$	52,388	$	89,505	$	-10,015	$	-51,625
	Earnings (loss) per average share of common stock:
	Basic^(a)	$	1.01	$	1.73	$	-0.19	$	-1
	Diluted^(a)	$	1.01	$	1.73	$	-0.19	$	-1
	Washington Gas Light Company
	Operating revenues	$	355,817	$	535,950	$	180,882	$	127,708
	Operating income (loss)	$	72,167	$	134,490	$	-235	$	-55,289
	Net income (loss) applicable to common stock	$	38,387	$	76,935	$	-4,531	$	-39,789

	Fiscal Year 2012
	WGL Holdings, Inc.
	Operating revenues	$	727,757	$	839,444	$	438,326	$	419,783
	Operating income	$	93,925	$	138,411	$	20,533	$	13,114
	Net income applicable to common stock	$	50,438	$	74,179	$	7,457	$	7,744
	Earnings per average share of common stock:
	Basic^(a)	$	0.98	$	1.44	$	0.14	$	0.15
	Diluted^(a)	$	0.98	$	1.44	$	0.14	$	0.15

	Washington Gas Light Company
	Operating revenues	$	370,893	$	471,057	$	164,667	$	131,049
	Operating income (loss)	$	84,219	$	135,657	$	-2,691	$	-1,917
	Net income (loss) applicable to common stock	$	44,176	$	72,142	$	-6,061	$	-1,531
	(a)The sum of quarterly per share amounts may not equal annual per share amounts as quarterly calculations are based on varying numbers of common shares.

Accounting_Policies_Narrative_

Accounting Policies (Narrative) (Details) (USD $)	12 Months Ended
Accounting Policies (Narrative) (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Accounting Policies Details Narrative [Abstract]	'	'	'
Increase (Decrease) In Allowance For Equity Funds Used During Constructio	($600,000)	$700,000	'
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	2.86%	2.87%	2.84%
Pretax AFUDC Rate	5.43%	7.40%	5.50%
Duration Of Cost Of Gas Recovered Or Refunded	'12 months	'	'
Indexed Or Fixed Rate Customer Contracts Terms	'Customer contracts, which typically have terms less than 24 months, but may extend up to five years.	'	'
WGL Holdings, Inc.	'	'	'
Inventory Adjustments [Abstract]	'	'	'
Lower Of Cost Or Market Adjustment Storage Gas Inventory	10,100,000	22,400,000	800,000
Washington Gas Light Company	'	'	'
Inventory Adjustments [Abstract]	'	'	'
Lower Of Cost Or Market Adjustment Storage Gas Inventory	0	1,400,000	300,000
Natural Gas Customers [Member] \| WGL Holdings, Inc.	'	'	'
Customer Related Information [Abstract]	'	'	'
WGEServices Number Of Customers	168,000	'	'
Chillum Member [Member]	'	'	'
Accounting Policies Details Narrative [Abstract]	'	'	'
Impairment loss	500,000	0	0
Springfield Operations Center [Member] \| WGL Holdings, Inc.	'	'	'
Accounting Policies Details Narrative [Abstract]	'	'	'
Impairment loss	2,600,000	5,015,000	0
Springfield Operations Center [Member] \| Washington Gas Light Company	'	'	'
Accounting Policies Details Narrative [Abstract]	'	'	'
Impairment loss	$2,600,000	$5,015,000	0
Interruptible Customers [Member] \| Washington Gas Light Company	'	'	'
Customer Related Information [Abstract]	'	'	'
Percentage Of Total Gas Deliveries	15.20%	'	'
Firm Customer [Member] \| Washington Gas Light Company	'	'	'
Customer Related Information [Abstract]	'	'	'
Percentage Of Total Gas Deliveries	74.70%	'	'
Electric Generation Customers [Member] \| Washington Gas Light Company	'	'	'
Customer Related Information [Abstract]	'	'	'
Percentage Of Total Gas Deliveries	10.10%	'	'
Electricity Customers [Member] \| WGL Holdings, Inc.	'	'	'
Customer Related Information [Abstract]	'	'	'
WGEServices Number Of Customers	180,000	'	'

Accounting_Policies_Tables_Det

Accounting Policies (Tables) (Details) (USD $)	12 Months Ended
Accounting Policies (Tables) (Details) (USD $)	Sep. 30, 2013		Sep. 30, 2012
Asset Retirement Obligations Details [Line Items]	'		'
Short Term Asset Retirement Obligation	$2,700,000		$1,300,000
Schedule Of Property Plant And Equipment At Original Cost [Line Items]	'		'
Public Utilities, Property, Plant and Equipment, Transmission, Distribution and Storage	3,356,100,000		3,176,400,000
Public Utilities Property Plant And Equipment Construction Work In Progress	150,800,000		113,200,000
General, miscellaneous and intangibles	430,600,000		428,300,000
Transmission And Distribution Percentage	81.50%		83.40%
General, miscellaneous and intangibles percentage	10.40%		11.30%
Construction Work In Progress Percentage	3.70%		3.00%
Property Plant And Equipment Percentage for Segments	95.60%		97.70%
Property Plant And Equipment Total Percentage	100.00%		100.00%
Regulated Operation [Member]	'		'
Schedule Of Property Plant And Equipment At Original Cost [Line Items]	'		'
Total Property, Plant and Equipment for Segments	3,937,500,000		3,717,900,000
Property Plant And Equipment Percentage for Segments	95.60%		97.70%
Unregulated Operation [Member]	'		'
Schedule Of Property Plant And Equipment At Original Cost [Line Items]	'		'
Total Property, Plant and Equipment for Segments	180,600,000		89,100,000
Property Plant And Equipment Percentage for Segments	4.40%		2.30%
WGL Holdings, Inc.	'		'
Asset Retirement Obligations Details [Line Items]	'		'
Asset Retirement Obligation, Beginning Balance	72,700,000	[1]	69,500,000
Asset Retirement Obligation, Liabilities Incurred	1,200,000		1,900,000
Asset Retirement Obligation, Liabilities Settled	-1,000,000		-1,000,000
Asset Retirement Obligation, Accretion Expense	3,300,000		3,300,000
Asset Retirement Obligation, Revision of Estimate	27,800,000	[2]	-1,000,000	[2]
Asset Retirement Obligation, Ending Balance	104,000,000	[1]	72,700,000	[1]
Schedule Of Property Plant And Equipment At Original Cost [Line Items]	'		'
Property, Plant and Equipment, Gross, Total	4,118,149,000		3,807,036,000
Washington Gas Light Company	'		'
Asset Retirement Obligations Details [Line Items]	'		'
Asset Retirement Obligation, Beginning Balance	71,500,000	[1]	68,300,000
Asset Retirement Obligation, Liabilities Incurred	1,100,000		1,900,000
Asset Retirement Obligation, Liabilities Settled	-1,000,000		-1,000,000
Asset Retirement Obligation, Accretion Expense	3,300,000		3,300,000
Asset Retirement Obligation, Revision of Estimate	27,800,000	[2]	-1,000,000	[2]
Asset Retirement Obligation, Ending Balance	102,700,000	[1]	71,500,000	[1]
Schedule Of Property Plant And Equipment At Original Cost [Line Items]	'		'
Property, Plant and Equipment, Gross, Total	$3,903,482,000		$3,686,192,000

[1]	Includes short-term asset retirement obligations of $2.7 million and $1.3 million for fiscal year 2013 and 2012, 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 driving by our accelerated pipeline replacement programs.

Accounting_Policies_Operating_

Accounting Policies - Operating Leases (Details) (Leasehold Improvements [Member])	12 Months Ended
	Sep. 30, 2013
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, 2013		Sep. 30, 2012
Asset Recoverable Gas Costs	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Current	$0	[1]	$16,900,000	[1]
Regulatory Liabilities, Current	23,400,000	[1]	11,100,000	[1]
Interruptible Sharing	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Current	10,700,000		400,000
Regulatory Liabilities, Current	1,900,000		2,100,000
Revenue Subject to Refund	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Current	0		0
Regulatory Liabilities, Current	0		5,100,000
Conservation And Rate Making Efficiency Adjustment	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Current	100,000		23,300,000
Regulatory Liabilities, Current	1,500,000		0
Plant Recovery Mechanisms	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Current	0		100,000
Regulatory Liabilities, Current	200,000		2,400,000
Other Current Regulatory Assets Or Liabilities	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Current	0		100,000
Regulatory Liabilities, Current	0		0
Total current	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Current	10,800,000		40,800,000
Regulatory Liabilities, Current	27,000,000		20,700,000
Accrued Asset Removal Costs	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	0		0
Regulatory Liability, Noncurrent	321,300,000		325,600,000
Deferred Fuel Costs	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	94,000,000	[1]	0	[1]
Regulatory Liability, Noncurrent	0	[1]	19,500,000	[1]
Other PostretirementBenefit	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	700,000	[2]	1,100,000	[2]
Regulatory Liability, Noncurrent	0	[2]	0	[2]
Pension Costs	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	51,000,000	[2]	45,200,000	[2]
Regulatory Liability, Noncurrent	0	[2]	0	[2]
Total pension and other post-retirement benefits	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	240,800,000		435,100,000
Regulatory Liability, Noncurrent	0		0
Income tax-related amounts due from to customers	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets	24,900,000	[3]	28,800,000	[3]
Regulatory Liabilities	4,500,000	[3]	5,000,000	[3]
Unrecognized Pension Cost	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	155,100,000	[1],[4]	289,600,000	[1],[4]
Regulatory Liability, Noncurrent	0	[1],[4]	0	[1],[4]
Unrecognized Other Post Retirement Benefits	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	34,000,000	[1],[4]	99,200,000	[1],[4]
Regulatory Liability, Noncurrent	0	[1],[4]	0	[1],[4]
Deferred Gain (Loss) on Early Extinguishment of Debt	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets	11,600,000	[1],[5]	12,500,000	[1],[5]
Regulatory Liabilities	600,000	[1],[5]	900,000	[1],[5]
Deferred Gain On Sale Of Assets	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets	0	[1]	0	[1]
Regulatory Liabilities	1,700,000	[1]	2,000,000	[1]
Environmental response costs	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets	600,000	[1]	4,400,000	[1]
Regulatory Liabilities	0	[1]	0	[1]
Rights Of Way Fee	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets	0		0
Regulatory Liabilities	1,600,000		600,000
Other Costs Business Process Outsourcing	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets	1,400,000	[1]	1,800,000	[1]
Regulatory Liabilities	0	[1]	0	[1]
Non Retirement Postemployment Benefits	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets	15,400,000	[1],[6]	16,300,000	[1],[6]
Regulatory Liabilities	0	[1],[6]	0	[1],[6]
Other Regulatory Expenses	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets	11,900,000	[7]	4,600,000	[7]
Regulatory Liabilities	5,100,000	[7]	6,500,000	[7]
Other Regulatory Expenses \| Chillum LNG	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets	7,900,000	[7]	'
Total Other	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	65,800,000		68,400,000
Regulatory Liability, Noncurrent	13,500,000		15,000,000
Total Deferred	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets, Noncurrent	400,600,000		503,500,000
Regulatory Liability, Noncurrent	334,800,000		360,100,000
Total	'		'
Schedule of Regulatory Assets and Liabilities [Line Items]	'		'
Regulatory Assets	411,400,000		544,300,000
Regulatory Liabilities	$361,800,000		$380,800,000

[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]	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.
[4]	Refer to Note 10-Pension and Other Post-Retirement Benefit Plans for a further discussion of these amounts.
[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]	The balance includes a $7.9 million asset related to the recoverable portion of the Chillum LNG facility.

Accounts_Payable_and_Other_Acc2

Accounts Payable and Other Accrued Liabilities (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012
WGL Holdings, Inc.	'	'
Accounts payable - trade	$216,300,000	$217,000,000
Employee benefits and payroll accruals	23,400,000	20,300,000
Embedded derivatives and other accrued liabilities	30,900,000	33,100,000
Accounts Payable and Accrued Liabilities, Current, Total	270,658,000	270,387,000
Washington Gas Light Company	'	'
Accounts payable - trade	99,700,000	112,700,000
Employee benefits and payroll accruals	21,400,000	18,200,000
Embedded derivatives and other accrued liabilities	11,700,000	11,300,000
Accounts Payable and Accrued Liabilities, Current, Total	$132,814,000	$142,193,000

ShortTerm_Debt_Details

Short-Term Debt (Details) (USD $)	Sep. 30, 2013		Sep. 30, 2012
Line Of Credit Facility [Line Items]	'		'
Unsecured revolving credit facility	$800,000,000	[1]	$800,000,000	[2]
Less: Commercial Paper	-373,100,000		-247,700,000
Net committed credit available	426,900,000		552,300,000
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.	'		'
Line Of Credit Facility [Line Items]	'		'
Less: Commercial Paper	373,100,000		247,700,000
Revolving credit facility maximum borrowing capacity	550,000,000		550,000,000
Revolving credit facility additional borrowings	100,000,000		100,000,000
Short-term debt weighted average interest rate	0.19%		0.26%
Washington Gas Light Company	'		'
Line Of Credit Facility [Line Items]	'		'
Unsecured revolving credit facility	350,000,000	[1]	350,000,000	[2]
Less: Commercial Paper	124,500,000		98,800,000
Net committed credit available	225,500,000		251,200,000
Revolving credit facility maximum borrowing capacity	450,000,000		450,000,000
Revolving credit facility additional borrowings	100,000,000		100,000,000
Short-term debt weighted average interest rate	0.13%		0.23%
Non Utility [Member]	'		'
Line Of Credit Facility [Line Items]	'		'
Unsecured revolving credit facility	450,000,000	[1]	450,000,000	[2]
Less: Commercial Paper	-248,600,000		-148,900,000
Net committed credit available	$201,400,000		$301,100,000

[1]	Both WGL Holdings and Washington Gas have the right to request extensions with the banksb approval. WGL Holdingsb 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 $)	Sep. 30, 2013	Sep. 30, 2012
Long Term Debt Narrative [Abstract]	'	'
Debt Instrument Unused Borrowing Capacity Amount	$450,000,000	'
Medium Term Notes	583,000,000	583,000,000
Longterm Debt Weighted Average Interest Rate	5.91%	5.91%
Unamortized Discount on Long Term Debt Maturities	$29,907	'

LongTerm_Debt_Maturities_Detai

Long-Term Debt - Maturities (Details) (USD $)	Sep. 30, 2013
2014	$67,000,000	[1]
2015	20,000,000	[1]
2016	25,000,000	[1]
2017	0	[1]
2018	0	[1]
Thereafter	471,000,000	[1]
Total (before project debt financing)	583,000,000	[1]
Long Term Debt Project Financing	8,100,000	[1],[2]
Total	591,100,000	[1]
Less-current maturities	67,000,000	[1]
Total non-current	524,100,000	[1]
Medium-term Notes [Member]	'
2014	67,000,000	[1]
2015	20,000,000	[1]
2016	25,000,000	[1]
2017	0	[1]
2018	0	[1]
Thereafter	471,000,000	[1]
Total (before project debt financing)	583,000,000	[1]
Long Term Debt Project Financing	0	[1],[2]
Total	583,000,000	[1]
Less-current maturities	67,000,000	[1]
Total non-current	516,000,000	[1]
Other Long Term Debt [Member]	'
2014	0	[1]
2015	0	[1]
2016	0	[1]
2017	0	[1]
2018	0	[1]
Thereafter	0	[1]
Total (before project debt financing)	0	[1]
Long Term Debt Project Financing	8,100,000	[1],[2]
Total	8,100,000	[1]
Less-current maturities	0	[1]
Total non-current	$8,100,000	[1]

[1]	Excludes unamortized discounts of $29,907 at September 30, 2013.
[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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2012
In Millions, unless otherwise specified	FirstMortgageMember	FirstMortgageMember	Issuances [Member]	Issuances [Member]	Retirements [Member]	Retirements [Member]	October 17 2011 [Member]	October 19 2011 [Member]	October 19 2011 B [Member]	February 27 2012 [Member]	June 19 2012 [Member]
							Retirements [Member]	Retirements [Member]	Retirements [Member]	Retirements [Member]	Retirements [Member]
Issuance and Retirements [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Principal	$0	$0	$0	$0	$0	$77	$7	$15	$5	$25	$25
Interest rate	'	'	'	'	'	'	6.05%	6.00%	6.00%	6.00%	5.90%
Nominal Maturity Date	'	'	'	'	'	'	17-Oct-11	19-Oct-11	19-Oct-11	27-Feb-12	19-Jun-12

Common_Stock_Details

Common Stock (Details)	Sep. 30, 2013		Sep. 30, 2012
Common Stock Details Narrative [Abstract]	'		'
Common Stock, Shares, Outstanding	51,774,204		51,611,647
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]	'		'
Omnibus Incentive Compensation Plan	1,054,437	[1]	'
Dividend Reinvestment and Common Stock Purchase Plan	2,963,895		'
Employee Savings Plans	637,196		'
Directors' Stock Compensation Plan	113,626		'
Total Common Stock Reserves Shares	4,769,154		'
Footnote Details [Abstract]	'		'
Incentive Compensation Plan Stock Options	26,372		'
Performance Shares	295,973		'

[1]	Effective MarchB 1, 2007, WGL Holdings 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 295,973B shares dedicated to performance shares granted but not vested and include 26,372 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, 2013	Sep. 30, 2012
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, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2011

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2011

WGL Holdings, Inc.

Earnings Per Share Disclosure [Line Items]

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

($51,625)

($10,015)

$89,505

$52,388

$7,744

$7,457

$74,179

$50,438

$80,253

$139,818

$117,050

Average common shares outstanding-basic

51,697,000

51,522,000

51,195,000

Basic earnings per average common share

($1)

[1]

($0.19)

[1]

$1.73

[1]

$1.01

[1]

$0.15

[1]

$0.14

[1]

$1.44

[1]

$0.98

[1]

$1.55

$2.71

$2.29

Stock-based compensation plan

111

100

Total average common shares outstanding diluted

51,808,000

51,589,000

51,295,000

Diluted EPS

($1)

[1]

($0.19)

[1]

$1.73

[1]

$1.01

[1]

$0.15

[1]

$0.14

[1]

$1.44

[1]

$0.98

[1]

$1.55

$2.71

$2.28

[1]

The sum of quarterly per share amounts may not equal annual per share amounts as quarterly calculations are based on varying numbers of common shares.

Income_Taxes_Narrative_Details

Income Taxes (Narrative) (Details) (Washington Gas Light Company, USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Washington Gas Light Company	'	'	'
Tax savings realized from tax sharing agreement	$1.30	$0.30	'
Expected Increase In Effective Tax Rate Due to Med D Tax Benefit Elimination	1.00%	'	'
Unrecognized Tax Benefits, Period Increase (Decrease)	3	'	'
Interest Expense For Uncertain Tax Position	'	$1.60	$0.70

Income_Taxes_Components_of_Inc

Income Taxes (Components of Income Tax Expense) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
WGL Holdings, Inc.	'	'	'
Current:	'	'	'
Federal	$41,425	($13,188)	$18,531
State	11,258	-30	10,899
Current Income Tax Expense (Benefit), Total	52,683	-13,218	29,430
Deferred	'	'	'
Deferred Income Tax Expense (Benefit), Total	1,431	107,699	58,694
Amortization of investment tax credits	-1,822	-1,132	-974
Income Tax Expense (Benefit), Continuing Operations, Total	52,292	93,349	87,150
Washington Gas Light Company	'	'	'
Current:	'	'	'
Federal	40,492	-13,155	9,415
State	7,515	-3,332	7,162
Current Income Tax Expense (Benefit), Total	48,007	-16,487	16,577
Deferred	'	'	'
Deferred Income Tax Expense (Benefit), Total	-2,915	89,132	40,102
Amortization of investment tax credits	-895	-898	-893
Income Tax Expense (Benefit), Continuing Operations, Total	44,197	71,747	55,786
Accelerated Depreciation [Member] \| WGL Holdings, Inc.	'	'	'
Deferred	'	'	'
Federal	33,394	45,506	37,924
State	6,795	9,412	6,689
Accelerated Depreciation [Member] \| Washington Gas Light Company	'	'	'
Deferred	'	'	'
Federal	34,518	45,661	37,363
State	6,770	9,423	6,595
Other Federal [Member] \| WGL Holdings, Inc.	'	'	'
Deferred	'	'	'
Federal	-31,173	44,727	12,067
State	-7,585	8,054	2,014
Other Federal [Member] \| Washington Gas Light Company	'	'	'
Deferred	'	'	'
Federal	-35,982	27,851	-3,216
State	($8,221)	$6,197	($640)

Income_Taxes_Tax_Rate_Reconcil

Income Taxes (Tax Rate Reconciliation) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
WGL Holdings, Inc.	'	'	'
Income taxes at statutory federal tax rate	$46,853	$82,070	$71,932
Accelerated depreciation less amount deferred	2,106	1,178	1,981
Amortization of investment tax credits	-1,822	-1,132	-974
Cost Of Removal	-2,356	-2,291	-1,160
State income taxes-net of federal benefit	7,448	12,068	10,631
Medicare D adjustment	0	2,827	4,714
Other items-net	63	-1,371	26
Income Tax Expense (Benefit), Continuing Operations, Total	52,292	93,349	87,150
Statutory federal income tax rate (%)	35.00%	35.00%	35.00%
Accelerated depreciation less amount deferred (%)	1.57%	0.50%	0.96%
Amortization of investment tax credits (%)	-1.36%	-0.48%	-0.47%
Cost of removal (%)	-1.76%	-0.98%	-0.56%
State income taxes-net of federal benefit (%)	5.56%	5.15%	5.17%
Medicare D adjustment (%)	0.00%	1.21%	2.29%
Other items-net (%)	0.05%	-0.59%	0.02%
Effective Income Tax Rate, Continuing Operations, Total	39.06%	39.81%	42.41%
Washington Gas Light Company	'	'	'
Income taxes at statutory federal tax rate	40,782	63,628	43,882
Accelerated depreciation less amount deferred	2,106	1,178	1,981
Amortization of investment tax credits	-895	-898	-893
Cost Of Removal	-2,356	-2,291	-1,160
State income taxes-net of federal benefit	5,487	8,916	6,390
Consolidated tax sharing allocation	-1,290	-309	15
Medicare D adjustment	0	2,827	4,714
Other items-net	363	-1,304	857
Income Tax Expense (Benefit), Continuing Operations, Total	$44,197	$71,747	$55,786
Statutory federal income tax rate (%)	35.00%	35.00%	35.00%
Accelerated depreciation less amount deferred (%)	1.81%	0.65%	1.58%
Amortization of investment tax credits (%)	-0.77%	-0.49%	-0.71%
Cost of removal (%)	-2.02%	-1.26%	-0.93%
State income taxes-net of federal benefit (%)	4.71%	4.90%	5.10%
Consolidated tax sharing allocation (%)	-1.11%	-0.17%	0.01%
Medicare D adjustment (%)	0.00%	1.56%	3.76%
Other items-net (%)	0.31%	-0.72%	0.68%
Effective Income Tax Rate, Continuing Operations, Total	37.93%	39.47%	44.49%

Income_Taxes_Components_of_Def

Income Taxes (Components of Deferred Tax Assets) (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Current [Member] \| WGL Holdings, Inc.	'	'
Deferred Income Tax Assets:	'	'
Pensions	$0	$0
Other post-retirement benefits	0	0
Uncollectible accounts	8,127	7,891
Inventory overheads	6,431	7,104
Capital gains/losses-net	2	155
Valuation allowance	-2	-155
Employee compensation and benefits	5,876	5,355
Customer advances	0	0
Derivatives	0	0
Deferred gas costs	4,911	0
Other	816	810
Total assets	26,161	21,160
Deferred Income Tax Liabilities:	'	'
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	0	4,670
Derivatives	1,639	4,086
Total liabilities	1,639	8,756
Net accumulated deferred income tax assets (liabilities)	24,522	12,404
Current [Member] \| Washington Gas Light Company	'	'
Deferred Income Tax Assets:	'	'
Pensions	0	0
Other post-retirement benefits	0	0
Uncollectible accounts	6,948	6,823
Inventory overheads	6,431	7,105
Employee compensation and benefits	5,756	5,205
Customer advances	0	0
Derivatives	2,138	0
Deferred gas costs	4,911	0
Other	816	810
Total assets	27,000	19,943
Deferred Income Tax Liabilities:	'	'
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	0	4,670
Derivatives	0	857
Other	0	0
Total liabilities	0	5,527
Net accumulated deferred income tax assets (liabilities)	27,000	14,416
Non-current [Member] \| WGL Holdings, Inc.	'	'
Deferred Income Tax Assets:	'	'
Pensions	17,362	56,053
Other post-retirement benefits	18,510	46,814
Uncollectible accounts	0	0
Inventory overheads	0	0
Capital gains/losses-net	0	0
Valuation allowance	0	0
Employee compensation and benefits	37,301	26,145
Customer advances	197	198
Derivatives	7,872	0
Deferred gas costs	0	0
Other	4,161	1,172
Total assets	85,403	130,382
Deferred Income Tax Liabilities:	'	'
Accelerated depreciation and other plant related items	596,754	545,006
Losses/gains on reacquired debt	1,567	1,758
Income taxes recoverable through future rates	112,222	194,149
Deferred gas costs	4,667	3,522
Derivatives	0	7,398
Total liabilities	715,210	751,833
Net accumulated deferred income tax assets (liabilities)	-629,807	-621,451
Non-current [Member] \| Washington Gas Light Company	'	'
Deferred Income Tax Assets:	'	'
Pensions	16,768	55,289
Other post-retirement benefits	18,474	46,502
Uncollectible accounts	0	0
Inventory overheads	0	0
Employee compensation and benefits	27,125	25,613
Customer advances	197	197
Derivatives	7,872	0
Deferred gas costs	0	0
Other	2,039	0
Total assets	72,475	127,601
Deferred Income Tax Liabilities:	'	'
Accelerated depreciation and other plant related items	565,996	527,633
Losses/gains on reacquired debt	1,567	1,758
Income taxes recoverable through future rates	111,698	193,076
Deferred gas costs	4,667	3,521
Derivatives	0	7,399
Other	0	152
Total liabilities	683,928	733,539
Net accumulated deferred income tax assets (liabilities)	($611,453)	($605,938)

Income_Taxes_Unrecognized_Tax_

Income Taxes (Unrecognized Tax Benefits) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	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	$22,082	$20,699
Increases resulting from current period tax positions	5,251	3,396
Decreases resulting from prior period tax positions	-2,282	-2,013
Total unrecognized tax benefits, ending balance	$25,051	$22,082

Recovered_Sheet1

Pension and Other Post-retirement Benefit Plans (Narrative) (Details) (USD $)	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Defined Benefit Plan Accumulated Other Comprehensive Income Net Transition Assets Obligations After Tax	$190,600,000	'	'
Contributions by Employer	3,500,000	3,400,000	3,200,000
Defined Contribution Plan Employer Discretionary Contribution Amount	800,000	600,000	'
The projected benefit obligation (PBO)	788,700,000	888,400,000	'
The projected accumulated benefit obligation (ABO)	737,200,000	819,900,000	'
The PBO for the non-funded DB SERP	47,800,000	48,000,000	'
The ABO for the non-funded DB SERP	43,900,000	40,600,000	'
The PBO for the non-funded DB SERP restoration	800,000	700,000	'
The ABO for the non-funded DB SERP restoration	500,000	300,000	'
Percentage Of Prior Years Asset Gains And Losses Recognized	20.00%	'	'
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%	'	'
Health Care Cost Trend Rates For Medicare And Non Medicare Eligible Retirees	7.50%	7.50%	'
Future Healthcare Cost Trend Rates	5.00%	'	'
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%	'	'
Mutual Funds Investment Category [Abstract]	'	'	'
Corporate Debt In The Banking And Finance Industrials And Utilities Sectors	70.00%	70.00%	'
Mutual Funds Equity Securities Of Non US Companies	30.00%	30.00%	'
Investments In Commingled Funds And Pooled Separate Accounts [Abstract]	'	'	'
Common Stock Of Large Cap US Companies	67.00%	71.00%	'
Short Term Money Market Investments	1.00%	11.00%	'
Equity Securities Of Non US Companies	20.00%	8.00%	'
Non Residential Income Producing Properties Located In The United States	12.00%	10.00%	'
Defined Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year 1	0	'	'
Prescription Drug Subsidy Receipts Next Twelve Months	0	'	'
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]	'	'	'
Contributions by Employer	800,000	400,000	400,000
WGL Holdings, Inc.	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Accumulated Other Comprehensive Income (Loss), Net of Tax	-11,048,000	-12,201,000	'
Washington Gas Light Company	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Accumulated Other Comprehensive Income (Loss), Net of Tax	-11,048,000	-12,201,000	'
Pension Plans Defined Benefit [Member]	'	'	'
Investments In Commingled Funds And Pooled Separate Accounts [Abstract]	'	'	'
Defined Benefit Plan Employer Payment Current Fiscal Year	0	'	'
Other PostretirementBenefit Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Assumed Income Tax Rate	41.50%	'	'
Investments In Commingled Funds And Pooled Separate Accounts [Abstract]	'	'	'
Defined Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year 1	10,000,000	'	'
Defined Benefit Plan Employer Payment Current Fiscal Year	18,000,000	'	'
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 [Member]	'	'	'
Investments In Commingled Funds And Pooled Separate Accounts [Abstract]	'	'	'
Defined Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year 1	3,500,000	'	'
Defined Benefit Plan Employer Payment Current Fiscal Year	$1,800,000	'	'

Recovered_Sheet2

Pension and Other Post-retirement Benefit Plans (Table 1) (Details) (USD $)	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Change in plan assets	'	'	'
Fair value of plan assets at end of year	$21,100,000	$18,700,000	$16,800,000
Pension Plans Defined Benefit [Member]	'	'	'
Change in projected benefit obligation	'	'	'
Benefit obligation at beginning of year	937,200,000	787,000,000	'
Service cost	17,000,000	12,900,000	12,100,000
Interest cost	36,600,000	40,500,000	41,300,000
Actuarial Loss	-110,000,000	142,800,000	'
Retiree Contributions	0	0	'
Benefits Paid	-43,400,000	-46,000,000	'
Projected benefit obligation at end of year	837,400,000	937,200,000	787,000,000
Change in plan assets	'	'	'
Fair Value of plan assets at beginning of year	750,600,000	600,000,000	'
Actual return on plan assets	38,600,000	117,100,000	'
Contributions by Employer	1,800,000	82,000,000	'
Retiree Contributions And Medicare Part D Reimbursements	0	0	'
Expenses	-2,400,000	-2,500,000	'
Benefits Paid	-43,400,000	-46,000,000	'
Fair value of plan assets at end of year	745,200,000	750,600,000	600,000,000
Funded status at end of year	-92,200,000	-186,600,000	'
Total Recognized	'	'	'
Current Liability	-3,500,000	-3,000,000	'
Accrued pensions and benefits	-88,700,000	-183,600,000	'
Total Recognized	-92,200,000	-186,600,000	'
Other PostretirementBenefit Plans Defined Benefit [Member]	'	'	'
Change in projected benefit obligation	'	'	'
Benefit obligation at beginning of year	480,100,000	502,000,000	'
Service cost	9,600,000	8,000,000	7,400,000
Interest cost	18,800,000	25,100,000	25,100,000
Actuarial Loss	-62,300,000	-36,100,000	'
Retiree Contributions	4,600,000	3,900,000	'
Benefits Paid	-21,000,000	-22,800,000	'
Projected benefit obligation at end of year	429,800,000	480,100,000	502,000,000
Change in plan assets	'	'	'
Fair Value of plan assets at beginning of year	358,300,000	296,500,000	'
Actual return on plan assets	19,900,000	57,700,000	'
Contributions by Employer	18,000,000	24,200,000	'
Retiree Contributions And Medicare Part D Reimbursements	5,700,000	2,700,000	'
Expenses	0	0	'
Benefits Paid	-21,000,000	-22,800,000	'
Fair value of plan assets at end of year	380,900,000	358,300,000	296,500,000
Funded status at end of year	-48,900,000	-121,800,000	'
Total Recognized	'	'	'
Current Liability	0	0	'
Accrued pensions and benefits	-48,900,000	-121,800,000	'
Total Recognized	($48,900,000)	($121,800,000)	'

Pension_and_Other_Postretireme2

Pension and Other Post-retirement Benefit Plans (Table 2) (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Unrecognized Costs/Income Recorded on the Balance Sheet	'	'
Accumulated Cther Comprehensive Loss Tax Effect	$7.90	$8.80
Pension Plans Defined Benefit [Member]	'	'
Unrecognized Costs/Income Recorded on the Balance Sheet	'	'
Unrecognized actuarial net loss	171.1	304
Unrecognized prior service cost (credit)	1.3	2.4
Unrecognized transition obligation	0	0
Total	172.4	306.4
Regulatory asset	155.1	289.6
Accumulated Cther Comprehensive Loss Tax Effect	17.3	16.8
Defined Benefit Plan Recorded On Balance Sheet Before Tax	172.4	306.4
Other PostretirementBenefit Plans Defined Benefit [Member]	'	'
Unrecognized Costs/Income Recorded on the Balance Sheet	'	'
Unrecognized actuarial net loss	55.3	128
Unrecognized prior service cost (credit)	-22.4	-26.4
Unrecognized transition obligation	0	1.1
Total	32.9	102.7
Regulatory asset	31.3	99.2
Accumulated Cther Comprehensive Loss Tax Effect	1.6	3.5
Defined Benefit Plan Recorded On Balance Sheet Before Tax	$32.90	$102.70

Pension_and_Other_Postretireme3

Pension and Other Post-retirement Benefit Plans (Table 3) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
Pension Plans Defined Benefit [Member] \| Regulatory Assets Liabilities [Member]	'
Amounts Recognized During Fiscal Year	'
Actuarial net loss	$27.20
Prior service cost (credit)	0.9
Transition obligation	0
Total	28.1
Amounts to be Rcognized During Fiscal Year	'
Actuarial net loss	15.5
Prior service cost (credit)	0.2
Transition obligation	0
Total	15.7
Pension Plans Defined Benefit [Member] \| Accumulated Other Comprehensive Loss, Net of Taxes	'
Amounts Recognized During Fiscal Year	'
Actuarial net loss	1.5
Prior service cost (credit)	0.1
Transition obligation	0
Total	1.6
Amounts to be Rcognized During Fiscal Year	'
Actuarial net loss	1.3
Prior service cost (credit)	0.1
Transition obligation	0
Total	1.4
Other PostretirementBenefit Plans Defined Benefit [Member] \| Regulatory Assets Liabilities [Member]	'
Amounts Recognized During Fiscal Year	'
Actuarial net loss	8.9
Prior service cost (credit)	-3.8
Transition obligation	0.8
Total	5.9
Amounts to be Rcognized During Fiscal Year	'
Actuarial net loss	-7.5
Prior service cost (credit)	3.2
Transition obligation	0
Total	-4.3
Other PostretirementBenefit Plans Defined Benefit [Member] \| Accumulated Other Comprehensive Loss, Net of Taxes	'
Amounts Recognized During Fiscal Year	'
Actuarial net loss	0.3
Prior service cost (credit)	-0.1
Transition obligation	0.2
Total	0.4
Amounts to be Rcognized During Fiscal Year	'
Actuarial net loss	-0.3
Prior service cost (credit)	0.1
Transition obligation	0
Total	($0.20)

Pension_and_Other_Postretireme4

Pension and Other Post-retirement Benefit Plans (Table 4) (Details) (USD $)	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
WGL Holdings, Inc.	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Recognized prior service cost	$1,671,000	$640,000	($135,000)
Recognized actuarial loss	-3,399,000	2,125,000	3,743,000
Amortization of transition obligation	-238,000	-239,000	-5,000
Washington Gas Light Company	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Recognized prior service cost	1,671,000	640,000	-135,000
Recognized actuarial loss	-3,399,000	2,125,000	3,743,000
Amortization of transition obligation	-238,000	-239,000	-5,000
Pension Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Service cost	17,000,000	12,900,000	12,100,000
Interest cost	36,600,000	40,500,000	41,300,000
Expected return on plan assets	-41,900,000	-43,500,000	-44,600,000
Recognized prior service cost	1,000,000	1,000,000	1,100,000
Recognized actuarial loss	28,700,000	16,100,000	14,700,000
Amortization of transition obligation	0	0	0
Net periodic benefit cost	41,400,000	27,000,000	24,600,000
Amount allocated to construction projects	-5,700,000	-3,400,000	-2,900,000
Amount deferred as regulatory asset (liability)-net	-3,700,000	-7,500,000	-7,100,000
Amount charged (credited) to expense	32,000,000	16,100,000	14,600,000
Other PostretirementBenefit Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Service cost	9,600,000	8,000,000	7,400,000
Interest cost	18,800,000	25,100,000	25,100,000
Expected return on plan assets	-18,300,000	-18,800,000	-18,500,000
Recognized prior service cost	-3,900,000	-3,900,000	-3,900,000
Recognized actuarial loss	9,200,000	13,300,000	11,200,000
Amortization of transition obligation	1,100,000	1,100,000	1,100,000
Net periodic benefit cost	16,500,000	24,800,000	22,400,000
Amount allocated to construction projects	-2,800,000	-3,700,000	-3,500,000
Amount deferred as regulatory asset (liability)-net	2,400,000	1,500,000	2,100,000
Amount charged (credited) to expense	$16,100,000	$22,600,000	$21,000,000

Pension_and_Other_Postretireme5

Pension and Other Post-retirement Benefit Plans (Table 5) (Details)	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Pension Plans Defined Benefit [Member]	'	'	'
Benefit Obligations Assumptions [Abstract]	'	'	'
Discount rate	'	4.00%	'
Net Periodic Benefit Cost Assumptions [Abstract]	'	'	'
Discount rate	4.00%	5.30%	5.50%
Expected long-term return on plan assets	6.75%	7.50%	7.50%
Rate of compensation increase	'	'	3.25%
Pension Plans Defined Benefit [Member] \| Maximum [Member]	'	'	'
Benefit Obligations Assumptions [Abstract]	'	'	'
Discount rate	5.00%	'	'
Rate of compensation increase	5.15%	5.15%	'
Net Periodic Benefit Cost Assumptions [Abstract]	'	'	'
Rate of compensation increase	5.15%	5.15%	'
Pension Plans Defined Benefit [Member] \| Minimum [Member]	'	'	'
Benefit Obligations Assumptions [Abstract]	'	'	'
Discount rate	4.50%	'	'
Rate of compensation increase	3.85%	3.85%	'
Net Periodic Benefit Cost Assumptions [Abstract]	'	'	'
Rate of compensation increase	3.85%	3.85%	'
Other PostretirementBenefit Plans Defined Benefit [Member]	'	'	'
Benefit Obligations Assumptions [Abstract]	'	'	'
Discount rate	5.10%	4.00%	'
Rate of compensation increase	3.85%	3.85%	'
Net Periodic Benefit Cost Assumptions [Abstract]	'	'	'
Discount rate	4.00%	5.10%	5.75%
Expected long-term return on plan assets	6.75%	7.40%	7.50%
Rate of compensation increase	3.85%	'	3.25%
Other PostretirementBenefit Plans Defined Benefit [Member] \| Maximum [Member]	'	'	'
Net Periodic Benefit Cost Assumptions [Abstract]	'	'	'
Rate of compensation increase	'	5.15%	'
Other PostretirementBenefit Plans Defined Benefit [Member] \| Minimum [Member]	'	'	'
Net Periodic Benefit Cost Assumptions [Abstract]	'	'	'
Rate of compensation increase	'	3.85%	'

Pension_and_Other_Postretireme6

Pension and Other Post-retirement Benefit Plans (Table 6) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]	'
Increase one percentage point total service and interest cost components	$6.10
Decrease one percentage point total service and interest cost components	-4.6
Increase one percentage point post-retirement benefit obligation	61
Decrease one percentage point post-retirement benefit obligation	($50.20)

Pension_and_Other_Postretireme7

Pension and Other Post-retirement Benefit Plans (Table 7) (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan assets at end of year	$21.10	$18.70	$16.80
Pension Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	748.4	775.3	'
Receivable (Payable)	-3.2	-24.7	'
Fair value of plan assets at end of year	745.2	750.6	600
Percentage of fair value of plan investments	100.40%	103.30%	'
Percent Receivable (Payable)	-0.40%	-3.30%	'
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	379.8	356.8	'
Receivable (Payable)	-1.1	-1.5	'
Fair value of plan assets at end of year	380.9	358.3	296.5
Percentage of fair value of plan investments	99.70%	100.00%	'
Percent Receivable (Payable)	-0.30%	0.00%	'
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	32.4	64.9	'
Level 1 [Member] \| Other PostretirementBenefit Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	0.6	0.3	'
Level 2 [Member] \| Pension Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	694.9	691.7	'
Level 2 [Member] \| Other PostretirementBenefit Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	379.2	356.5	'
Level 3 [Member] \| Pension Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	21.1	18.7	'
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	0.9	0.8	'
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	0.6	0.3	'
Percentage of fair value of plan investments	0.20%	0.10%	'
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	0.9	0.8	'
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	0.6	0.3	'
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	31.5	32	'
Percentage of fair value of plan investments	4.20%	4.30%	'
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	31.5	32	'
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	124.5	115.6	'
Percentage of fair value of plan investments	16.70%	15.40%	'
US Treasury Securities [Member] \| Other PostretirementBenefit Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	23.6	61.1	'
Percentage of fair value of plan investments	6.20%	17.10%	'
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	124.5	115.6	'
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	23.6	61.1	'
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	1.7	4.6	'
Percentage of fair value of plan investments	0.40%	1.30%	'
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	1.7	4.6	'
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]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Total plan assets percent	34.00%	'	'
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	19	20.1	'
Percentage of fair value of plan investments	2.50%	2.70%	'
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	19	20.1	'
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	93.6	84.2	'
Percentage of fair value of plan investments	12.60%	11.20%	'
Domestic Corporate Debt Securities [Member] \| Other PostretirementBenefit Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	28.7	60.7	'
Percentage of fair value of plan investments	7.50%	17.00%	'
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	93.6	84.2	'
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	28.7	60.7	'
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	1.9	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	1.9	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	'
US States and Political Subdivisions Debt Securities [Member] \| Pension Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	9	9.4	'
Percentage of fair value of plan investments	1.20%	1.20%	'
US States and Political Subdivisions Debt Securities [Member] \| Other PostretirementBenefit Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	4.1	9.6	'
Percentage of fair value of plan investments	1.10%	2.70%	'
US States and Political Subdivisions 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	'
US States and Political Subdivisions 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 States and Political Subdivisions Debt Securities [Member] \| Level 2 [Member] \| Pension Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	9	9.4	'
US States and Political Subdivisions 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	4.1	9.6	'
US States and Political Subdivisions 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	'
US States and Political Subdivisions 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	'
Foreign Corporate Debt Securities [Member] \| Pension Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	18.4	11.7	'
Percentage of fair value of plan investments	2.50%	1.60%	'
Foreign Corporate Debt Securities [Member] \| Other PostretirementBenefit Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	4.6	10.5	'
Percentage of fair value of plan investments	1.20%	2.90%	'
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	18.4	11.7	'
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	4.6	10.5	'
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	1	19.1	'
Percentage of fair value of plan investments	0.10%	2.50%	'
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	0	'
Repurchase Agreements [Member] \| Level 2 [Member] \| Pension Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	1	19.1	'
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	0	'
Fixed Income Securities Other [Member] \| Pension Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	5.7	8.1	'
Percentage of fair value of plan investments	0.80%	1.10%	'
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	9.1	'
Percentage of fair value of plan investments	1.40%	2.60%	'
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	0	'
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	0	'
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	5.7	8.1	'
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	9.1	'
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	0	'
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	0	'
Mutual Funds [Member] \| Pension Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	93.2	108	'
Percentage of fair value of plan investments	12.50%	14.40%	'
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	32.1	'
Mutual Funds [Member] \| Level 2 [Member] \| Pension Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	93.2	75.9	'
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	0	'
Commingled Funds [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Total plan assets percent	66.00%	'	'
Commingled Funds [Member] \| Other PostretirementBenefit Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	311.2	200.9	'
Percentage of fair value of plan investments	81.70%	56.30%	'
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	0	'
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	311.2	200.9	'
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	0	'
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	316.6	364.6	'
Percentage of fair value of plan investments	42.50%	48.60%	'
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	0	'
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	295.5	345.9	'
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	21.1	18.7	'
Private Equity / Limited Partnership \| Pension Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	33.3	'	'
Percentage of fair value of plan investments	4.50%	'	'
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	'	'
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	33.3	'	'
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	'	'
Futures Contract [Member] \| Pension Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	-0.3	-0.3	'
Percentage of fair value of plan investments	0.00%	0.00%	'
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	0	'
Futures Contract [Member] \| Level 2 [Member] \| Pension Plans Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Information about Plan Assets [Abstract]	'	'	'
Fair value of plan investments	-0.3	-0.3	'
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	$0	'

Pension_and_Other_Postretireme8

Pension and Other Post-retirement Benefit Plans (Table 8) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Changes in fair value of the Level 3 assets [Abstract]	'	'
Fair Value of plan assets at beginning of year	$18.70	$16.80
Assets still held at year end	2.4	1.9
Fair value of plan assets at end of year	$21.10	$18.70

Pension_and_Other_Postretireme9

Pension and Other Post-retirement Benefit Plans (Table 9) (Details) (USD $)	Sep. 30, 2013
In Millions, unless otherwise specified	Sep. 30, 2013
Pension Plans Defined Benefit [Member]	'
Expected Benefit Payments [Abstract]	'
2014	$48.40
2015	49.6
2016	50.4
2017	51.9
2018	53
2019-2023	281.8
Other PostretirementBenefit Plans Defined Benefit [Member]	'
Expected Benefit Payments [Abstract]	'
2014	18.7
2015	19.7
2016	20.8
2017	21.8
2018	22.7
2019-2023	$121.30

Share_Based_Compensation_Narra

Share Based Compensation (Narrative) (Details) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'
Compensation expense recognized	$6.50		$3.60	$4.40
Unrecognized compensation expense	8.1		'	'
Weighted-average period remaining to recognize unrecognized compensation expense	'1 year 8 months		'	'
Tax benefit from compensation expense	2.6		1.4	1.8
Performances Shares [Member]	'		'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'
Unrecognized compensation expense	3.8		'	'
Intrinsic Value Performance Shares Vested	0		3.3	4.6
Minimum percentage of performance shares issued	0.00%		'	'
Maximum percentage of performance shares issued	200.00%		'	'
Shares granted during the period	109,665	[1]	'	'
Weighted-average grant date fair value, vested	$0		'	'
Performance Units [Member]	'		'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'
Unrecognized compensation expense	4.3		'	'
Value of performance units vested	$1		'	'
Fair value of units expected to vest	3.2		'	'
Cash To Settle Performance Unit Awards	0		2.8	4.2
Shares granted during the period	4,413,992		'	'
Liability for Equity Option Awards Outstanding	4.9		2.1	4.7
Stock Option [Member]	'		'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'
Cash received from stock options exercised	0		0.8	4.1
Tax benefit realized from exercised stock options	0		0.1	0.4
Plan 1999 [Member]	'		'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'
Shares authorized for issue under plan	2,000,000		'	'
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		0.5	0.5
Tax benefit from compensation expense	$0.30		$0.20	$0.20
Shares granted during the period	16,600		11,900	14,800
Weighted-average grant date fair value, vested	$40.46		$44.30	$36.74

[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
Stock Based Compensation (Table 1) (Details) (USD $)	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2011
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	272,172	[1]	'		'
Granted	109,665	[1]	'		'
Vested	0	[1]	'		'
Cancelled/Forfeited	-85,864	[1]	'		'
Non-vested and outstanding, end of year	295,973	[1]	272,172	[1]	'
Weighted-average grant date fair value, non-vested and outstanding, beginning of year	$38.20		'		'
Weighted-average grant date fair value, granted	$39.73		$38.99		$41.14
Weighted-average grant date fair value, vested	$0		'		'
Weighted-average grant date fair value, cancelled/forfeited	$34.37		'		'
Weighted-average grant date fair value, non-vested and outstanding, end of year	$39.88		$38.20		'
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	10,034,413		'		'
Granted	4,413,992		'		'
Cancelled/Forfeited	-2,865,849		'		'
Non-vested and outstanding, end of year	11,582,556		'		'

[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
Stock Based Compensation (Table 2) (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Performances Shares [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]	'	'	'
Expected stock-price volatility	19.40%	27.80%	29.00%
Dividend yield	3.98%	3.97%	4.00%
Weighted-average grant date fair value, granted	$39.73	$38.99	$41.14
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	17.80%	'	'
Performance Units [Member] \| Grant 2011 [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]	'	'	'
Expected stock-price volatility	16.70%	'	'

Stock_Based_Compensation_Table3

Stock Based Compensation (Table 3) (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Stock options outstanding, beginning	26,372	'
Stock options granted	0	'
Stock options exercised	0	'
Stock options exercisable	26,372	'
Stock options cancelled/forfeited	0	'
Stock options outstanding, end of year	26,372	26,372
Weighted-average exercise price, outstanding	$31.34	$31.34
Weighted-average exercise price, granted	$0	'
Weighted-average exercise price, exercised	$0	'
Weighted-average exercise price, cancelled/forfeited	$0	'
Weighted-average exercise price, exercisable	$31.34	'
Weighted-average remaining contractual term, outstanding	'4 years 0 months	'4 years 0 months
Weighted-average remaining contractual term, exercisable	'4 years 0 months	'
Aggregate intrinsic value, outstanding	$235	$235
Aggregate intrinsic value, exercisable	235	'
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	0	'
Aggregate Intrinsic Value - Cancelled	$0	'

Environmental_Matter_Narrative

Environmental Matter (Narrative) (Details) (Washington Gas Light Company)	12 Months Ended
	Sep. 30, 2013
Number of Sites	10
DC [Member]	'
RegulatoryAssetRecoveryAssessments	'Rate orders issued by the PSC of DC allow Washington Gas a three-year recovery
MD [Member]	'
RegulatoryAssetRecoveryAssessments	'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

Environmental_Matters_Details

Environmental Matters (Details) (Washington Gas Light Company, USD $)	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Schedule of Regulatory Assets and Liabilities [Line Items]	'	'
Regulatory Assets, Noncurrent	$65,824,000	$68,429,000
Accrual for Environmental Loss Contingencies	8,500,000	8,400,000
Environmental Exit Costs, Reasonably Possible Additional Losses, High Estimate	20,500,000	17,300,000
Environmental response costs	'	'
Schedule of Regulatory Assets and Liabilities [Line Items]	'	'
Regulatory Assets, Noncurrent	$600,000	$4,400,000

Commitments_and_Contingencies_

Commitments and Contingencies (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
	Counterparties	Sep. 30, 2012	Sep. 30, 2011
Commitments and Contingencies [Line Items]	'	'	'
Recorded Unconditional Purchase Obligation	$506.40	'	'
Operating Leases, Rent Expense	5.6	5.2	5
Future purchase commitment of natural gas	94.8	'	'
Construction Project Financing	6.7	6.2	'
Number Of Service Agreements With Pipeline Companies	4	'	'
Maximum [Member]	'	'	'
Commitments and Contingencies [Line Items]	'	'	'
Pipeline Service Agreements Expiration Dates Range	'2029	'	'
Other Agreements And Peaking Services Expiration Dates Range	'2027	'	'
Asset Optimization Pipeline Transportation Storage And Peaking Contracts Range	'2028	'	'
Minimum [Member]	'	'	'
Commitments and Contingencies [Line Items]	'	'	'
Pipeline Service Agreements Expiration Dates Range	'2014	'	'
Other Agreements And Peaking Services Expiration Dates Range	'2014	'	'
Asset Optimization Pipeline Transportation Storage And Peaking Contracts Range	'2014	'	'
Retail Energy Marketing [Member]	'	'	'
Commitments and Contingencies [Line Items]	'	'	'
Recorded Unconditional Purchase Obligation	305.4	'	'
Subsidiary of Common Parent [Member]	'	'	'
Commitments and Contingencies [Line Items]	'	'	'
Recorded Unconditional Purchase Obligation	193.2	'	'
Other Non Utility [Member]	'	'	'
Commitments and Contingencies [Line Items]	'	'	'
Recorded Unconditional Purchase Obligation	7.8	'	'
October 2013 [Member]	'	'	'
Commitments and Contingencies [Line Items]	'	'	'
Recorded Unconditional Purchase Obligation	6	'	'
MD [Member] \| April 26 2013	'	'	'
Commitments and Contingencies [Line Items]	'	'	'
Requested Overall Rate Of Return	8.70%	'	'
Requested Rate Of Return On Common Equity	10.70%	'	'
MD [Member] \| April 26 2013 \| Overall increase [Member]	'	'	'
Commitments and Contingencies [Line Items]	'	'	'
Requested Increase In Utility Revenue	30.8	'	'
MD [Member] \| May 31 2013	'	'	'
Commitments and Contingencies [Line Items]	'	'	'
Requested Increase In Utility Revenue Revision	28.3	'	'
MD [Member] \| October 10 2013	'	'	'
Commitments and Contingencies [Line Items]	'	'	'
Recommended Overall Rate Of Return	7.54%	'	'
Recommended Rate Of Return On Common Equity	9.25%	'	'
Recommended Annual Revenue Increase	$8.80	'	'
MD [Member] \| October 24 2013 [Member]	'	'	'
Commitments and Contingencies [Line Items]	'	'	'
Requested Rate Of Return On Common Equity	9.60%	'	'

Commitments_and_Contingencies_1

Commitments and Contingencies (Narrative - Therms) (Details)	Sep. 30, 2013
	Therms
Commitments and Contingencies Disclosure [Abstract]	'
Purchases Natural Gas Under Asset Optimization	1,186,500,000
Purchases Natural Gas Offset By Matching Sales Contract	96,900,000

Committments_and_Contingencies1

Committments and Contingencies - Tables (Details) (USD $)	Sep. 30, 2013
In Millions, unless otherwise specified	Sep. 30, 2013
Minimum Payments Under Operating Leases [Abstract]	'
Operating Leases, Future Minimum Payments Due, Current	$5.70
Operating Leases, Future Minimum Payments, Due in Two Years	5.8
Operating Leases, Future Minimum Payments, Due in Three Years	4.9
Operating Leases, Future Minimum Payments, Due in Four Years	4
Operating Leases, Future Minimum Payments, Due in Five Years	3.6
Operating Leases, Future Minimum Payments, Due Thereafter	1.8
Operating Leases, Future Minimum Payments Due	25.8
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	589.9
Unrecorded Unconditional Purchase Obligation, Due within Two Years	266.6
Unrecorded Unconditional Purchase Obligation, Due within Three Years	88.9
Unrecorded Unconditional Purchase Obligation, Due within Four Years	49.9
Unrecorded Unconditional Purchase Obligation, Due within Five Years	44.7
Unrecorded Unconditional Purchase Obligation, Due after Five Years	520.6
Unrecorded Unconditional Purchase Obligation	1,560.60
Washington Gas Light Company	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	187.9
Unrecorded Unconditional Purchase Obligation, Due within Two Years	197.1
Unrecorded Unconditional Purchase Obligation, Due within Three Years	226.9
Unrecorded Unconditional Purchase Obligation, Due within Four Years	220.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years	213.1
Unrecorded Unconditional Purchase Obligation, Due after Five Years	1,383.10
Unrecorded Unconditional Purchase Obligation	2,428.90
Gas Purchase Committments [Member]	'
Footnote Details [Abstract]	'
Commitments Related To Renewable Energy Credits	7.2
Gas Purchase Committments [Member] \| Retail Energy Marketing [Member]	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	162.7
Unrecorded Unconditional Purchase Obligation, Due within Two Years	66.5
Unrecorded Unconditional Purchase Obligation, Due within Three Years	19.7
Unrecorded Unconditional Purchase Obligation, Due within Four Years	2.4
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation	251.3
Gas Purchase Committments [Member] \| WGL Midstream	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	16.2
Unrecorded Unconditional Purchase Obligation, Due within Two Years	5.6
Unrecorded Unconditional Purchase Obligation, Due within Three Years	2.4
Unrecorded Unconditional Purchase Obligation, Due within Four Years	28.1
Unrecorded Unconditional Purchase Obligation, Due within Five Years	29
Unrecorded Unconditional Purchase Obligation, Due after Five Years	397.5
Unrecorded Unconditional Purchase Obligation	478.8
Electric Purchase Committments [Member] \| Retail Energy Marketing [Member]	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	391.5
Unrecorded Unconditional Purchase Obligation, Due within Two Years	180.9
Unrecorded Unconditional Purchase Obligation, Due within Three Years	48.5
Unrecorded Unconditional Purchase Obligation, Due within Four Years	2.6
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0.2
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation	623.7
Pipeline Contracts [Member] \| Retail Energy Marketing [Member]	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	2.5
Unrecorded Unconditional Purchase Obligation, Due within Two Years	0.6
Unrecorded Unconditional Purchase Obligation, Due within Three Years	0.6
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0.6
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0.6
Unrecorded Unconditional Purchase Obligation, Due after Five Years	1.8
Unrecorded Unconditional Purchase Obligation	6.7
Pipeline Contracts [Member] \| WGL Midstream	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	17
Unrecorded Unconditional Purchase Obligation, Due within Two Years	13
Unrecorded Unconditional Purchase Obligation, Due within Three Years	17.7
Unrecorded Unconditional Purchase Obligation, Due within Four Years	16.2
Unrecorded Unconditional Purchase Obligation, Due within Five Years	14.9
Unrecorded Unconditional Purchase Obligation, Due after Five Years	121.3
Unrecorded Unconditional Purchase Obligation	$200.10

Derivative_and_Weather_Related2

Derivative and Weather Related Instruments (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Asset Optimization [Abstract]	'	'	'
Gain (Loss) on Asset Optimization Transactions Net Pretax	($33.20)	$28.30	$1.90
Unrealized Gains (Loss) On Asset Optimization Derivative Instruments Net Pretax	-45.4	15.9	-13.2
WGEServices	'	'	'
Derivative, Collateral [Abstract]	'	'	'
Right to Reclaim Cash	12.1	8.2	'
Collateral Already Posted Aggregate Fair Value	3.6	2.6	'
WGL Midstream	'	'	'
Derivative, Collateral [Abstract]	'	'	'
Right to Reclaim Cash	8.1	3.7	'
WGL Holdings, Inc.	'	'	'
Absolute Notional Amounts of Open Positions on Derivative Instruments	'	'	'
Interest Rate Swap Notional Principal Value	75	0	'
Warrant Transaction Volume	4.6	4.4	'
Balance Sheet Classification of Derivative Instruments	'	'	'
Derivative Assets	120.3	191.2	'
Derivative Liabilities	-247.8	-137.6	'
Netting of Collateral	0.9	1.5	'
Total	-126.6	55.1	'
WGL Holdings, Inc. \| Current assets- derivatives	'	'	'
Balance Sheet Classification of Derivative Instruments	'	'	'
Derivative Assets	57.3	80.4	'
Derivative Liabilities	-19.3	-36.1	'
Netting of Collateral	-2.7	-1.1	'
Total	35.3	43.2	'
WGL Holdings, Inc. \| Non current assets- derivatives	'	'	'
Balance Sheet Classification of Derivative Instruments	'	'	'
Derivative Assets	57.4	103.9	'
Derivative Liabilities	-31.1	-42.1	'
Netting of Collateral	0	0	'
Total	26.3	61.8	'
WGL Holdings, Inc. \| Accounts Payable And OtherAccrued Liabilities [Member]	'	'	'
Balance Sheet Classification of Derivative Instruments	'	'	'
Derivative Assets	1.5	-0.2	'
Derivative Liabilities	0	0	'
Netting of Collateral	0	0	'
Total	1.5	-0.2	'
WGL Holdings, Inc. \| Current liabilities- Derivatives	'	'	'
Balance Sheet Classification of Derivative Instruments	'	'	'
Derivative Assets	4.1	4.3	'
Derivative Liabilities	-53.4	-40.8	'
Netting of Collateral	0.9	0	'
Total	-48.4	-36.5	'
WGL Holdings, Inc. \| Non current liabilities- derivatives	'	'	'
Balance Sheet Classification of Derivative Instruments	'	'	'
Derivative Assets	0	2.8	'
Derivative Liabilities	-144	-18.6	'
Netting of Collateral	2.7	2.6	'
Total	-141.3	-13.2	'
WGL Holdings, Inc. \| Asset Optimization [Member]	'	'	'
Absolute Notional Amounts of Open Positions on Derivative Instruments	'	'	'
Natural Gas Derivative Transaction, Volume	13,289,600,000	4,798,500,000	'
WGL Holdings, Inc. \| Retail Sales [Member]	'	'	'
Absolute Notional Amounts of Open Positions on Derivative Instruments	'	'	'
Natural Gas Derivative Transaction, Volume	98,900,000	126,100,000	'
Electricity Derivative Transaction, Volume	4,790,200,000	5,080,500,000	'
WGL Holdings, Inc. \| Other Risk Management Activities [Member]	'	'	'
Absolute Notional Amounts of Open Positions on Derivative Instruments	'	'	'
Natural Gas Derivative Transaction, Volume	1,803,600,000	537,100,000	'
Electricity Derivative Transaction, Volume	17,647,900,000	16,898,000,000	'
Washington Gas Light Company	'	'	'
Derivative, Collateral [Abstract]	'	'	'
Right to Reclaim Cash	3	4	'
Derivative, Collateral, Obligation to Return Cash	4.6	9.3	'
Absolute Notional Amounts of Open Positions on Derivative Instruments	'	'	'
Interest Rate Swap Notional Principal Value	75	0	'
Warrant Transaction Volume	0	0	'
Balance Sheet Classification of Derivative Instruments	'	'	'
Derivative Assets	68	116.7	'
Derivative Liabilities	-175.7	-69.4	'
Netting of Collateral	-2.7	-1.1	'
Total	-110.4	46.2	'
Washington Gas Light Company \| Current assets- derivatives	'	'	'
Balance Sheet Classification of Derivative Instruments	'	'	'
Derivative Assets	19.3	20.7	'
Derivative Liabilities	-12.3	-10.4	'
Netting of Collateral	-2.7	-1.1	'
Total	4.3	9.2	'
Washington Gas Light Company \| Non current assets- derivatives	'	'	'
Balance Sheet Classification of Derivative Instruments	'	'	'
Derivative Assets	47.2	92.8	'
Derivative Liabilities	-31.1	-41.8	'
Netting of Collateral	0	0	'
Total	16.1	51	'
Washington Gas Light Company \| Current liabilities- Derivatives	'	'	'
Balance Sheet Classification of Derivative Instruments	'	'	'
Derivative Assets	1.5	1.6	'
Derivative Liabilities	-26.2	-12.1	'
Netting of Collateral	0	0	'
Total	-24.7	-10.5	'
Washington Gas Light Company \| Non current liabilities- derivatives	'	'	'
Balance Sheet Classification of Derivative Instruments	'	'	'
Derivative Assets	0	1.6	'
Derivative Liabilities	-106.1	-5.1	'
Netting of Collateral	0	0	'
Total	($106.10)	($3.50)	'
Washington Gas Light Company \| Asset Optimization [Member]	'	'	'
Absolute Notional Amounts of Open Positions on Derivative Instruments	'	'	'
Natural Gas Derivative Transaction, Volume	11,115,800,000	3,039,100,000	'
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	1,455,700,000	206,500,000	'
Electricity Derivative Transaction, Volume	0	0	'

Derivative_and_Weather_Related3

Derivative and Weather Related Instruments (Gains and Losses) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
WGL Holdings, Inc.	'	'	'
Gains and (Losses) on Derivative Instruments	'	'	'
Gains (Losses) On Derivative Instruments	($173.10)	$50.40	($9.70)
Potential Collateral Requirements for Derivative Liabilities with Credit-risk-Contingent Features	'	'	'
Derivative liabilities with credit-risk-contingent features	77	101.2	'
Maximum potential collateral requirements	33.6	35.7	'
WGL Holdings, Inc. \| Operating Revenues Non Utility [Member]	'	'	'
Gains and (Losses) on Derivative Instruments	'	'	'
Recorded to income	-9.9	19.2	-6.8
WGL Holdings, Inc. \| Utility Cost Of Gas [Member]	'	'	'
Gains and (Losses) on Derivative Instruments	'	'	'
Recorded to income	-45.9	22.3	-9.4
WGL Holdings, Inc. \| Non Utility Cost Of Energy Related Sales [Member]	'	'	'
Gains and (Losses) on Derivative Instruments	'	'	'
Recorded to income	-2.4	-34.2	19.2
WGL Holdings, Inc. \| Other Income [Member]	'	'	'
Gains and (Losses) on Derivative Instruments	'	'	'
Other income net	0.2	0.9	0
WGL Holdings, Inc. \| Gas Costs [Member]	'	'	'
Gains and (Losses) on Derivative Instruments	'	'	'
Recorded to regulatory assets/liabilities	-115.1	42.2	-18.9
WGL Holdings, Inc. \| Other Regulatory Assets Liability [Member]	'	'	'
Gains and (Losses) on Derivative Instruments	'	'	'
Recorded to regulatory assets/liabilities	0	0	6.2
Washington Gas Light Company	'	'	'
Gains and (Losses) on Derivative Instruments	'	'	'
Gains (Losses) On Derivative Instruments	-161	64.5	-22.1
Potential Collateral Requirements for Derivative Liabilities with Credit-risk-Contingent Features	'	'	'
Derivative liabilities with credit-risk-contingent features	44.7	60.8	'
Maximum potential collateral requirements	1.7	3.4	'
Washington Gas Light Company \| Utility Cost Of Gas [Member]	'	'	'
Gains and (Losses) on Derivative Instruments	'	'	'
Recorded to income	-45.9	22.3	-9.4
Washington Gas Light Company \| Gas Costs [Member]	'	'	'
Gains and (Losses) on Derivative Instruments	'	'	'
Recorded to regulatory assets/liabilities	-115.1	42.2	-18.9
Washington Gas Light Company \| Other Regulatory Assets Liability [Member]	'	'	'
Gains and (Losses) on Derivative Instruments	'	'	'
Recorded to regulatory assets/liabilities	$0	$0	$6.20

Derivative_and_Weather_Related4

Derivative and Weather Related Instruments (Details 2) (USD $)	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
WGEServices	'	'	'
Concentration of Credit Risk	'	'	'
Obligation to counterparties	$0.10	'	'
Percentage Of Credit Exposure	10.00%	'	'
Number of Counterparties	1	'	'
WGEServices \| Weather Instruments [Member]	'	'	'
Gain (Loss) On Derivative Instruments Net Pretax [Abstract]	'	'	'
Gain (losses) on weather related instruments, pretax	-0.8	11.8	-8.5
WGL Midstream	'	'	'
Concentration of Credit Risk	'	'	'
Obligation to counterparties	7.2	'	'
Percentage Of Credit Exposure	10.00%	'	'
Number of Counterparties	3	'	'
Washington Gas Light Company	'	'	'
Concentration of Credit Risk	'	'	'
Obligation to counterparties	15.5	'	'
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	($2.80)

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
WGL Holdings, Inc.	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	$120.30	$192.70
Liabilities	-247.8	-139.5
WGL Holdings, Inc. \| Natural Gas Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	93.8	166.6
Liabilities	-217.8	-103.6
WGL Holdings, Inc. \| Electricity Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	25.4	23.7
Liabilities	-30	-33.9
WGL Holdings, Inc. \| Weather Instruments [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	1.5
Liabilities	0	-2
WGL Holdings, Inc. \| Warrant	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	1.1	0.9
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] \| Weather Instruments [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] \| Warrant	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
WGL Holdings, Inc. \| Level 2 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	72.3	86.2
Liabilities	-48.1	-75.8
WGL Holdings, Inc. \| Level 2 [Member] \| Natural Gas Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	72.3	85.9
Liabilities	-41.1	-62.5
WGL Holdings, Inc. \| Level 2 [Member] \| Electricity Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0.3
Liabilities	-7	-13.3
WGL Holdings, Inc. \| Level 2 [Member] \| Weather Instruments [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
Liabilities	0	0
WGL Holdings, Inc. \| Level 2 [Member] \| Warrant	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
WGL Holdings, Inc. \| Level 3 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	48	106.5
Liabilities	-199.7	-63.7
WGL Holdings, Inc. \| Level 3 [Member] \| Natural Gas Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	21.5	80.7
Liabilities	-176.7	-41.1
WGL Holdings, Inc. \| Level 3 [Member] \| Electricity Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	25.4	23.4
Liabilities	-23	-20.6
WGL Holdings, Inc. \| Level 3 [Member] \| Weather Instruments [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	1.5
Liabilities	0	-2
WGL Holdings, Inc. \| Level 3 [Member] \| Warrant	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	1.1	0.9
Washington Gas Light Company	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	68	118.2
Liabilities	-175.7	-71.4
Washington Gas Light Company \| Natural Gas Related Derivatives [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	68	116.7
Liabilities	-175.7	-69.4
Washington Gas Light Company \| Weather Instruments [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	1.5
Liabilities	0	-2
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 1 [Member] \| Weather Instruments [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	51	41.4
Liabilities	-25.1	-29.7
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	51	41.4
Liabilities	-25.1	-29.7
Washington Gas Light Company \| Level 2 [Member] \| Weather Instruments [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	0
Liabilities	0	0
Washington Gas Light Company \| Level 3 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	17	76.8
Liabilities	-150.6	-41.7
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	17	75.3
Liabilities	-150.6	-39.7
Washington Gas Light Company \| Level 3 [Member] \| Weather Instruments [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]	'	'
Assets	0	1.5
Liabilities	$0	($2)

Fair_Value_Measurements_Reconc

Fair Value Measurements (Reconciliation with Level 3 Inputs) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
WGL Holdings, Inc.	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	$42.80	($12.10)	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	-94.8	-16.8	-7.2
Recorded to regulatory assets-gas costs	-115.3	25.7	'
Transfers out of Level 3	-18.1	-7.9	'
Sales (liability)	0	-2.1	'
Purchases	5.7	5.5	'
Settlements	28	50.5	'
Balance at end of period	-151.7	42.8	-12.1
WGL Holdings, Inc. \| Weather Instruments [Member]	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	-0.5	-1.4	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	1.2	7.9	'
Recorded to regulatory assets-gas costs	0	0	'
Transfers out of Level 3	-0.7	-6.3	'
Sales (liability)	0	-2.1	'
Purchases	0	1.4	'
Settlements	0	0	'
Balance at end of period	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	39.6	-3.9	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	-72.4	22.1	'
Recorded to regulatory assets-gas costs	-115.3	25.7	'
Transfers out of Level 3	-17.4	-1.6	'
Sales (liability)	0	0	'
Purchases	0	0	'
Settlements	10.3	-2.7	'
Balance at end of period	-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	2.8	-6.8	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	-23.8	-47.7	'
Recorded to regulatory assets-gas costs	0	0	'
Transfers out of Level 3	0	0	'
Sales (liability)	0	0	'
Purchases	5.7	4.1	'
Settlements	17.7	53.2	'
Balance at end of period	2.4	2.8	'
WGL Holdings, Inc. \| Warrant	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	0.9	0	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	0.2	0.9	'
Recorded to regulatory assets-gas costs	0	0	'
Transfers out of Level 3	0	0	'
Sales (liability)	0	0	'
Purchases	0	0	'
Settlements	0	0	'
Balance at end of period	1.1	0.9	'
Washington Gas Light Company	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	35.1	-6.3	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	-44.7	22.2	-7.8
Recorded to regulatory assets-gas costs	-115.3	25.7	'
Transfers out of Level 3	-18.1	-6.6	'
Sales (liability)	0	-2.1	'
Purchases	0	1.4	'
Settlements	9.4	0.8	'
Balance at end of period	-133.6	35.1	-6.3
Washington Gas Light Company \| Weather Instruments [Member]	'	'	'
Reconciliation of Fair Value Measurements Using Significant Level 3 Inputs	'	'	'
Balance at beginning of period	-0.5	-1.4	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	1.2	7.9	'
Recorded to regulatory assets-gas costs	0	0	'
Transfers out of Level 3	-0.7	-6.3	'
Sales (liability)	0	-2.1	'
Purchases	0	1.4	'
Settlements	0	0	'
Balance at end of period	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	35.6	-4.9	'
Realized and unrealized gains (losses)	'	'	'
Recorded to income	-45.9	14.3	'
Recorded to regulatory assets-gas costs	-115.3	25.7	'
Transfers out of Level 3	-17.4	-0.3	'
Sales (liability)	0	0	'
Purchases	0	0	'
Settlements	9.4	0.8	'
Balance at end of period	-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	'
Recorded to regulatory assets-gas costs	0	0	'
Transfers out of Level 3	0	0	'
Sales (liability)	0	0	'
Purchases	0	0	'
Settlements	0	0	'
Balance at end of period	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	'
Recorded to regulatory assets-gas costs	0	0	'
Transfers out of Level 3	0	0	'
Sales (liability)	0	0	'
Purchases	0	0	'
Settlements	0	0	'
Balance at end of period	$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, 2013	Sep. 30, 2012	Sep. 30, 2011
WGL Holdings, Inc.	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	($94.80)	($16.80)	($7.20)
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	-111.6	23.2	-11.4
Total Unrealized Gains (Losses)	-175.3	62	-9.1
WGL Holdings, Inc. \| Natural Gas Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-72.4	22.1	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	-111.6	23.2	'
Total Unrealized Gains (Losses)	-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	-23.8	-47.7	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	0	0	'
Total Unrealized Gains (Losses)	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	1.2	7.9	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	0	0	'
Total Unrealized Gains (Losses)	0	0.2	'
WGL Holdings, Inc. \| Warrant	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0.2	0.9	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	0	0	'
Total Unrealized Gains (Losses)	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	-36.1	-11.2	-15.2
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-18.7	9.1	4
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	-27	3	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-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	-9.1	-14.2	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	-45.8	14.3	-4.4
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-44.3	13.8	-3.9
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	-45.8	14.3	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	'
WGL Holdings, Inc. \| OtherIncomeMember	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0.2	0.9	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	'
WGL Holdings, Inc. \| OtherIncomeMember \| Warrant	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	0.2	0.9	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	-14.3	-28.7	15.8
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-0.9	14.8	2.9
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	0.4	4.8	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	-14.7	-33.5	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	1.2	7.9	-3.4
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0.2	-0.7
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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	1.2	7.9	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0	'
Washington Gas Light Company	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-44.7	22.2	-7.8
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	-111.6	23.2	-11.4
Total Unrealized Gains (Losses)	-155.9	37.2	-16
Washington Gas Light Company \| Natural Gas Related Derivatives [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	-45.9	14.3	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	-111.6	23.2	'
Total Unrealized Gains (Losses)	-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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	0	0	'
Total Unrealized Gains (Losses)	0	0	'
Washington Gas Light Company \| Weather Instruments [Member]	'	'	'
Realized and Unrealized Gains (Losses) Recorded to Income for Level 3 Measurements	'	'	'
Recorded to income	1.2	7.9	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	0	0	'
Total Unrealized Gains (Losses)	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to regulatory assets - gas costs	0	0	'
Total Unrealized Gains (Losses)	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	-45.9	14.3	-4.4
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-44.3	13.8	-3.9
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	-45.9	14.3	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	-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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	1.2	7.9	-3.4
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	0	0.2	-0.7
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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	1.2	7.9	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	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	'
Unrealized Gains (Losses) Recorded for Level 3 Measurements	'	'	'
Recorded to income	$0	$0	'

Fair_Value_Measurements_Fair_V

Fair Value Measurements (Fair Value of Financial Instruments) (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Commercial Paper	($373,100,000)	($247,700,000)
WGL Holdings, Inc.	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Commercial Paper	373,100,000	247,700,000
Washington Gas Light Company	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Commercial Paper	124,500,000	98,800,000
Carrying Amount \| WGL Holdings, Inc.	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Money Market Funds	6,500,000	7,200,000
Other Short Term Investments	100,000	800,000
Commercial Paper	373,100,000	247,700,000
Long-term debt	524,100,000	589,200,000
Carrying Amount \| Washington Gas Light Company	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Money Market Funds	3,100,000	4,100,000
Other Short Term Investments	100,000	800,000
Commercial Paper	124,500,000	98,800,000
Long-term debt	524,100,000	589,200,000
Fair Value \| WGL Holdings, Inc.	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Money Market Funds	6,500,000	7,200,000
Other Short Term Investments	100,000	800,000
Commercial Paper	373,100,000	247,700,000
Long-term debt	630,200,000	758,900,000
Fair Value \| Washington Gas Light Company	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Money Market Funds	3,100,000	4,100,000
Other Short Term Investments	100,000	800,000
Commercial Paper	124,500,000	98,800,000
Long-term debt	$630,200,000	$758,900,000

Fair_Value_Measurements_Quanti

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

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Natural Gas Related Derivatives [Member]

Electricity Related Derivatives [Member]

Discounted Cash Flow [Member]

Option Model [Member]

Discounted Cash Flow [Member]

Maximum [Member]

Minimum [Member]

Maximum [Member]

Minimum [Member]

Maximum [Member]

Minimum [Member]

Natural Gas Basis Price [Member]

Annualized Volatility Price [Member]

Natural Gas Basis Price [Member]

Annualized Volatility 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

($151,700,000)

$42,800,000

($12,100,000)

($155,200,000)

$39,600,000

($3,900,000)

$2,400,000

$2,800,000

($6,800,000)

Input Price

$2.21

$1.18

($1.78)

($0.25)

$0.63

$1.18

($0.18)

$0.05

$64.15

$64.70

($2.00)

($2.20)

Option Volatility Percentage

276.60%

236.03%

34.60%

37.80%

Fair_Value_Measurements_Quanti1

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

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Natural Gas Related Derivatives [Member]

Discounted Cash Flow [Member]

Option Model [Member]

Maximum [Member]

Minimum [Member]

Maximum [Member]

Minimum [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

($133,600,000)

$35,100,000

($6,300,000)

($133,600,000)

$35,600,000

($4,900,000)

Input Price

$2.21

$1.18

($1.78)

($0.25)

$0.63

$0.86

$0.02

$0.09

Option Volatility Percentage

276.60%

236.03%

46.80%

37.80%

Fair_Value_Measurements_Nonrec

Fair Value Measurements (Nonrecurring Basis) (Details) (Springfield Operations Center, USD $)	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
WGL Holdings, Inc.	'	'	'
Fair Value Measurements [Line Items]	'	'	'
Impairment loss	$2,600,000	$5,015,000	$0
Washington Gas Light Company	'	'	'
Fair Value Measurements [Line Items]	'	'	'
Carrying Amount Of Long Lived Assets Held For Use	24,900,000	29,900,000	'
Fair Value Of Long Lived Assets Held For Use	22,300,000	24,900,000	'
Impairment loss	$2,600,000	$5,015,000	$0

Operating_Segment_Reporting_De

Operating Segment Reporting (Details) (USD $)

3 Months Ended

12 Months Ended

In Thousands, unless otherwise specified

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2011

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2011

Regulated Operation [Member]

Segment Reporting Information [Line Items]

Operating Revenues

$1,200,357

[1]

$1,137,666

[1]

$1,288,539

[1]

Operating Expenses:

Cost of energy-related sales

521,508

421,539

619,637

Operation

242,819

226,852

229,206

Maintenance

49,269

52,494

48,292

Depreciation and amortization

100,438

94,998

90,289

Revenue taxes

81,422

74,244

83,729

Other

52,271

50,821

52,635

Total Operating Expenses

1,047,727

920,948

1,123,788

Operating Income (Loss), Total

152,630

216,718

164,751

Equity in earnings of unconsolidated affiliates

Other Income (Expense) - Net

1,017

2,574

2,577

Interest Expense

35,631

36,098

40,462

Dividends on Washington Gas preferred stock

1,320

INCOME TAX EXPENSE (BENEFIT)

44,883

72,178

56,374

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

71,813

109,696

69,172

Segment Reporting Information Additional Elements For Bank Presentation [Abstract]

Total Assets

3,486,296

3,516,046

3,486,296

3,516,046

3,392,003

Capital Expenditures

227,948

208,225

227,948

208,225

180,668

Equity Method Investments

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

Segment Reporting Information [Line Items]

Operating Revenues

1,279,364

[1]

1,267,070

[1]

1,443,156

[1]

Operating Expenses:

Cost of energy-related sales

1,164,831

1,139,162

1,300,887

Operation

49,574

52,161

52,024

Maintenance

Depreciation and amortization

726

735

650

Revenue taxes

6,831

5,776

5,551

Other

4,411

4,071

4,210

Total Operating Expenses

1,226,373

1,201,905

1,363,322

Operating Income (Loss), Total

52,991

65,165

79,834

Equity in earnings of unconsolidated affiliates

Other Income (Expense) - Net

273

Interest Expense

Dividends on Washington Gas preferred stock

INCOME TAX EXPENSE (BENEFIT)

20,227

25,876

30,839

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

33,024

39,331

48,970

Segment Reporting Information Additional Elements For Bank Presentation [Abstract]

Total Assets

403,082

361,801

403,082

361,801

333,414

Capital Expenditures

730

984

730

984

1,107

Equity Method Investments

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

Segment Reporting Information [Line Items]

Operating Revenues

35,217

[1]

60,325

[1]

39,190

[1]

Operating Expenses:

Cost of energy-related sales

24,450

51,149

33,885

Operation

6,875

5,414

5,249

Maintenance

Depreciation and amortization

2,411

1,261

351

Revenue taxes

Other

303

280

238

Total Operating Expenses

34,046

58,112

39,723

Operating Income (Loss), Total

1,171

2,213

-533

Equity in earnings of unconsolidated affiliates

1,070

947

-549

Other Income (Expense) - Net

778

-32

Interest Expense

234

Dividends on Washington Gas preferred stock

INCOME TAX EXPENSE (BENEFIT)

-206

760

-543

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

2,991

2,367

-524

Segment Reporting Information Additional Elements For Bank Presentation [Abstract]

Total Assets

318,995

148,407

318,995

148,407

58,603

Capital Expenditures

83,667

41,818

83,667

41,818

26,800

Equity Method Investments

54,977

23,346

54,977

23,346

7,551

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

Segment Reporting Information [Line Items]

Operating Revenues

-20,390

[1]

-11,221

[1]

4,574

[1]

Operating Expenses:

Cost of energy-related sales

Operation

8,683

2,860

1,015

Maintenance

Depreciation and amortization

124

116

Revenue taxes

Other

474

240

Total Operating Expenses

9,281

3,216

1,078

Operating Income (Loss), Total

-29,671

-14,437

3,496

Equity in earnings of unconsolidated affiliates

312

Other Income (Expense) - Net

Interest Expense

417

Dividends on Washington Gas preferred stock

INCOME TAX EXPENSE (BENEFIT)

-10,951

-5,347

1,313

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

-18,825

-9,090

2,183

Segment Reporting Information Additional Elements For Bank Presentation [Abstract]

Total Assets

231,368

169,456

231,368

169,456

87,400

Capital Expenditures

101

520

Equity Method Investments

6,448

Other Activities [Member] | Unregulated Operation [Member]

Segment Reporting Information [Line Items]

Operating Revenues

[1]

Operating Expenses:

Cost of energy-related sales

Operation

9,344

3,660

3,743

Maintenance

Depreciation and amortization

Revenue taxes

Other

Total Operating Expenses

9,441

3,676

3,773

Operating Income (Loss), Total

-9,441

-3,676

-3,773

Equity in earnings of unconsolidated affiliates

128

293

Other Income (Expense) - Net

644

1,145

306

Interest Expense

402

366

117

Dividends on Washington Gas preferred stock

INCOME TAX EXPENSE (BENEFIT)

-1,124

-118

-833

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

-7,947

-2,486

-2,751

Segment Reporting Information Additional Elements For Bank Presentation [Abstract]

Total Assets

290,440

211,038

290,440

211,038

85,217

Capital Expenditures

Equity Method Investments

Corporate Elimination [Member]

Segment Reporting Information [Line Items]

Operating Revenues

-28,410

[1]

-28,530

[1]

-23,958

[1]

Operating Expenses:

Cost of energy-related sales

-26,458

-26,802

-23,958

Operation

-197

-1,093

Maintenance

Depreciation and amortization

-415

-634

Revenue taxes

Other

-1

Total Operating Expenses

-27,070

-28,530

-23,958

Operating Income (Loss), Total

-1,340

Equity in earnings of unconsolidated affiliates

Other Income (Expense) - Net

-686

-38

-86

Interest Expense

-686

-38

-86

Dividends on Washington Gas preferred stock

INCOME TAX EXPENSE (BENEFIT)

-537

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

-803

Segment Reporting Information Additional Elements For Bank Presentation [Abstract]

Total Assets

-470,121

-295,801

-470,121

-295,801

-147,603

Capital Expenditures

Equity Method Investments

WGL Holdings, Inc.

Segment Reporting Information [Line Items]

Operating Revenues

409,901

478,118

891,383

686,736

419,783

438,326

839,444

727,757

2,466,138

[1]

2,425,310

[1]

2,751,501

[1]

Operating Expenses:

Cost of energy-related sales

1,684,331

1,585,048

1,930,451

Operation

317,098

289,854

291,237

Maintenance

49,269

52,494

48,292

Depreciation and amortization

103,284

96,476

91,325

Revenue taxes

88,260

80,028

89,280

Other

57,556

55,427

57,141

Total Operating Expenses

2,299,798

2,159,327

2,507,726

Operating Income (Loss), Total

-75,139

-8,981

155,715

94,745

13,114

20,533

138,411

93,925

166,340

265,983

243,775

Equity in earnings of unconsolidated affiliates

1,510

1,240

-549

Other Income (Expense) - Net

2,026

3,692

2,840

Interest Expense

36,011

36,428

40,546

Dividends on Washington Gas preferred stock

1,320

INCOME TAX EXPENSE (BENEFIT)

52,292

93,349

87,150

NET INCOME (LOSS) APPLICABLE TO COMMON STOCK

-51,625

-10,015

89,505

52,388

7,744

7,457

74,179

50,438

80,253

139,818

117,050

Segment Reporting Information Additional Elements For Bank Presentation [Abstract]

Total Assets

4,260,060

4,110,947

4,260,060

4,110,947

3,809,034

Capital Expenditures

312,345

251,128

312,345

251,128

209,095

Equity Method Investments

$61,425

$23,346

$61,425

$23,346

$7,551

[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.

Other_Investments_Narratives_D

Other Investments - Narratives (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Other Investments Narrative Details	'	'
Financing Receivable Recorded Investment Current	$5.80	'
WGL Holdings, Inc.	'	'
Other Investments Narrative Details	'	'
Direct Fiinancing Leases Receivable	29.2	3.4
Financing Receivable Recorded Investment Current	5.8	0.7
Assets	120.3	192.7
Anticipated Investment In Constitution	68	'
Constitution Ownership Percentage	10.00%	'
WGL Holdings, Inc. \| Warrant	'	'
Other Investments Narrative Details	'	'
Assets	1.1	0.9
Willams Partners L.P.	'	'
Other Investments Narrative Details	'	'
Constitution Ownership Percentage	41.00%	'
Cabot Oil And Gas Corporation	'	'
Other Investments Narrative Details	'	'
Constitution Ownership Percentage	25.00%	'
Piedmont Natural Gas	'	'
Other Investments Narrative Details	'	'
Constitution Ownership Percentage	24.00%	'
ASD Solar, LP	'	'
Other Investments Narrative Details	'	'
Equity Method Investment Carry Value Difference	30.4	'
American Solar Direct Holdings Inc. (ASDHI)	'	'
Other Investments Narrative Details	'	'
Cost Method Investment ASDHI	5.6	5.6
American Solar Direct Holdings Inc. (ASDHI) \| Warrant	'	'
Other Investments Narrative Details	'	'
Assets	$1.10	$1.10

Other_Investments_Financing_Le

Other Investments - Financing Leases Table (Details) (USD $)	Sep. 30, 2013
In Millions, unless otherwise specified	Sep. 30, 2013
Capital Leases Net Investment In Direct Financing Leases[Abstract]	'
2014	$5.80
2015	1.2
2016	1.2
2017	1.2
2018	1.2
Thereafter	13.2
Total	23.8
Direct Financing Leases - Unearned Income	0.7
Direct Financing Leases - Residual Value	5.4
Direct Financing Leases - Initial Direct Costs	$0.70

Other_Investments_Location_Tab

Other Investments - Location Table (Details) (USD $)	12 Months Ended
Other Investments - Location Table (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012
ASSETS	'	'
Investment in direct financing leases, capital leases	$23,800,000	'
Other	5,800,000	'
VIEs	'	'
ASSETS	'	'
Non-Consolidated Investments	55,400,000	23,700,000
Investment in direct financing leases, capital leases	23,400,000	2,700,000
Derivative Assets	0	0
Other	5,800,000	700,000
VIEs - Total assets	84,600,000	27,100,000
LIABILITIES	'	'
VIEs - Liabilities - Other	8,500,000	1,000,000
VIEs - Liabilities - Total Liabilities	8,500,000	1,000,000
INCOME	'	'
Earnings from equity method investments	1,000,000	1,200,000
Depreciation expense	100,000	0
Other Income	1,400,000	200,000
Net income	2,300,000	1,400,000
Non-VIEs	'	'
ASSETS	'	'
Non-Consolidated Investments	12,100,000	5,600,000
Investment in direct financing leases, capital leases	0	0
Derivative Assets	1,100,000	900,000
Other	0	0
Non VIEs - Total assets	13,200,000	6,500,000
LIABILITIES	'	'
Non VIEs - Liabilities - Other	0	0
Non VIEs - Liabilities - Total Liabilities	0	0
INCOME	'	'
Earnings from equity method investments	500,000	0
Depreciation expense	0	0
Other Income	0	700,000
Net income	500,000	700,000
Total	'	'
ASSETS	'	'
Non-Consolidated Investments	67,500,000	29,300,000
Investment in direct financing leases, capital leases	23,400,000	2,700,000
Derivative Assets	1,100,000	900,000
Other	5,800,000	700,000
Total assets	97,800,000	33,600,000
LIABILITIES	'	'
Total Liabilities Other	8,500,000	1,000,000
Total Liabilities	8,500,000	1,000,000
INCOME	'	'
Earnings from equity method investments	1,500,000	1,200,000
Depreciation expense	100,000	0
Other Income	1,400,000	900,000
Net income	$2,800,000	$2,100,000

Related_Party_Transactions_Det

Related Party Transactions (Details) (USD $)	12 Months Ended
Related Party Transactions (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
WGEServices	'	'	'
Related Party Transaction [Line Items]	'	'	'
Related Party Gas Imbalance - Payable	$1,000,000	'	'
Related Party Gas Imbalance - Receivable	'	2,800,000	'
Washington Gas Light Company	'	'	'
Related Party Transaction [Line Items]	'	'	'
Related Party Transaction, Revenues from Transactions with Related Party	25,000,000	26,800,000	24,000,000
Due from Related Parties, Current	7,200,000	5,500,000	'
Due to Related Parties, Current	20,600,000	28,500,000	'
Related Party Purchased Receivables	$106,600,000	$95,700,000	'

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, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2011
WGL Holdings, Inc.	'		'		'		'		'		'		'		'		'		'		'
Operating Revenues	$409,901		$478,118		$891,383		$686,736		$419,783		$438,326		$839,444		$727,757		$2,466,138	[1]	$2,425,310	[1]	$2,751,501	[1]
Operating Income (Loss)	-75,139		-8,981		155,715		94,745		13,114		20,533		138,411		93,925		166,340		265,983		243,775
NET INCOME (LOSS) APPLICABLE TO COMMON STOCK	-51,625		-10,015		89,505		52,388		7,744		7,457		74,179		50,438		80,253		139,818		117,050
Earnings Per Share [Abstract]	'		'		'		'		'		'		'		'		'		'		'
Basic	($1)	[2]	($0.19)	[2]	$1.73	[2]	$1.01	[2]	$0.15	[2]	$0.14	[2]	$1.44	[2]	$0.98	[2]	$1.55		$2.71		$2.29
Diluted	($1)	[2]	($0.19)	[2]	$1.73	[2]	$1.01	[2]	$0.15	[2]	$0.14	[2]	$1.44	[2]	$0.98	[2]	$1.55		$2.71		$2.28
Washington Gas Light Company	'		'		'		'		'		'		'		'		'		'		'
Operating Revenues	127,708		180,882		535,950		355,817		131,049		164,667		471,057		370,893		1,200,357		1,137,666		1,288,539
Operating Income (Loss)	-55,289		-235		134,490		72,167		-1,917		-2,691		135,657		84,219		151,133		215,268		163,244
NET INCOME (LOSS) APPLICABLE TO COMMON STOCK	($39,789)		($4,531)		$76,935		$38,387		($1,531)		($6,061)		$72,142		$44,176		$71,002		$108,726		$68,270

[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]	The sum of quarterly per share amounts may not equal annual per share amounts as quarterly calculations are based on varying numbers of common shares.

Quarterly_Financial_Informatio3

Quarterly Financial Information - Narrative (Details) (USD $)	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Retroactive Adjustment	$0	$2,300,000	$0
Refundable Gas Costs	0	500,000	0
Washington Gas	'	'	'
Medicare D adjustment	0	2,827,000	4,714,000
Chillum LNG	'	'	'
Impairment loss	500,000	0	0
Springfield Operations Center \| Washington Gas	'	'	'
Impairment loss	$2,600,000	$5,015,000	$0

Schedule_II_Details

Schedule II (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2011
WGL Holdings, Inc.	'		'		'
Valuation and Qualifying Accounts Disclosure [Line Items]	'		'		'
Valuation Allowances and Reserves, Beginning Balance	$19,792		$17,969		$20,306
Valuation Allowances and Reserves, Charged to Cost and Expense	9,527		18,316		18,455
Valuation Allowances and Reserves, Charged to Other Accounts	4,217	[1]	4,774	[1]	3,761	[1]
Valuation Allowances and Reserves, Deductions	13,103	[2]	21,267	[2]	24,553	[2]
Valuation Allowances and Reserves, Ending Balance	20,433		19,792		17,969
Washington Gas Light Company	'		'		'
Valuation and Qualifying Accounts Disclosure [Line Items]	'		'		'
Valuation Allowances and Reserves, Beginning Balance	17,129		15,863		16,704
Valuation Allowances and Reserves, Charged to Cost and Expense	7,024		12,794		13,800
Valuation Allowances and Reserves, Charged to Other Accounts	3,978	[1]	4,300	[1]	3,761	[1]
Valuation Allowances and Reserves, Deductions	10,633	[2]	15,828	[2]	18,402	[2]
Valuation Allowances and Reserves, Ending Balance	$17,498		$17,129		$15,863

[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.