Merger with Nicor (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended												11 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Sep. 30, 2009	Jun. 30, 2009	Mar. 31, 2009	Dec. 09, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 08, 2011
Business Combinations [Abstract]
Exchange ratio of Nicor stock to AGL Stock (in hundredths)														0.8382
Cash payment per share of Nicor Stock (in dollars per share)														$ 21.20
Business Acquisition Number Of Acquiree Common Stock Exchanged														45,500,000
Business Acquisition Equity Interest Issued Number Of Shares Issued														38,200,000
Acquisition Equity Interests Issued Or Issuable Price Per Share																		39.90
Business Acquisition Cost Of Equity Issued														$ 1,523
Business Acquisition Cost Of Debt Assumed														980
BusinessAcquisition Purchase Price Allocation Assets Acquired Liabilities Assumed Net														2,503
Business Acquisition Cash Paid For Shares Outstanding														966
Business Acquisition Cash Paid For Equity Awards														14
Finite Lived Intangible Assets Net [Abstract]
Business Acquisition Purchase Price Allocation Amortizable Intangible Assets														103
Intangible Assets Net Excluding Goodwill	105	105				3									105	3
Revenues And Earnings Of Business Acquisition [Abstract]
Revenues	209	790	295	375	878	665	346	359	1,003	638	307	377	995		2,338	2,373	2,317
Profit Loss	(24)														186	250	249
Basic earnings (loss) per common share attributable to AGL Resources Inc. common shareholders	$ (0.30)	$ 0.37	$ (0.04)	$ 0.23	$ 1.60	$ 0.82	$ 0.29	$ 0.17	$ 1.74	$ 0.92	$ 0.16	$ 0.26	$ 1.55		$ 2.14	$ 3.02	$ 2.89
Diluted earnings (loss) per common share attributable to AGL Resources Inc. common shareholders	$ (0.30)	$ 0.37	$ (0.04)	$ 0.23	$ 1.59	$ 0.81	$ 0.29	$ 0.17	$ 1.73	$ 0.92	$ 0.16	$ 0.26	$ 1.55		$ 2.12	$ 3.00	$ 2.88
Business Combination Acquired Receivables [Abstract]
Business Combination Acquired Receivables Gross Contractual Amount														400
Business Combination Acquired Receivables Estimated Uncollectible														24
Business Combination Acquired Receivables Fair Value														376
Goodwill RollForward
Goodwill	1,813	1,813				418				418					1,813	418	418
Business Acquisition Purchase Price Allocation Current Assets														932
Business Acquisition Purchase Price Allocation Property Plant And Equipment														3,202
Business Acquisition Purchase Price Allocation Goodwill Amount														1,395
Business Acquisition Purchase Price Allocation Other Noncurrent Assets														791
Business Acquisition Purchase Price Allocation Current Liabilities														(1,170)
Business Acquisition Purchase Price Allocation Noncurrent Liabilities														(2,048)
BusinessAcquisition Purchase Price Allocation Assets Acquired Liabilities Assumed Net														2,503
Business Acquisition Purchase Price Allocation Noncurrent Liabilities Long Term Debt	500	500												(599)	500
Transaction expenses associated with merger															68	6
Transaction expenses associated with merger, net of tax															55	4
Merger Related Expenses															86	10
Business Combination Transactions Expenses For Change In Controls															34
Business Combination Transactions Expenses For Change In Controls Net Of Taxes															31
Nicor's shareholders ownership percentage of the combined company														0.33
Business Acquisition Effective Date Of Acquisition														December 9, 2011
Business Acquisition Pro Forma Information [Abstract]
Business Acquisitions Pro Forma Revenue															4,715	5,083
Business Acquisitions Pro Forma Net Income Loss															313	343
Business Acquisition Pro Forma Earnings Per Share Basic															$ 2.69	$ 2.97
Business Acquisition Pro Forma Earnings Per Share Diluted															$ 2.68	$ 2.96
All Other Segments [Member]
Revenues And Earnings Of Business Acquisition [Abstract]
Revenues															(148)	(128)	(113)
Goodwill RollForward
Goodwill	8	8				0				0					8	0	0
Goodwill Acquired During Period														8
Distribution Operations [Member]
Revenues And Earnings Of Business Acquisition [Abstract]
Revenues															1,597	1,494	1,486
Goodwill RollForward
Goodwill	1,586	1,586				404				404					1,586	404	404
Goodwill Acquired During Period														1,182
Retail Operations [Member]
Revenues And Earnings Of Business Acquisition [Abstract]
Revenues															702	840	801
Goodwill RollForward
Goodwill	124	124				0				0					124	0	0
Goodwill Acquired During Period														124
Retail Operations [Member] | Trade Names [Member]
Finite Lived Intangible Assets Net [Abstract]
Business Acquisition Purchase Price Allocation Amortizable Intangible Assets														33
Acquired Finite Lived Intangible Asset Weighted Average Useful Life (in Years)															15
Retail Operations [Member] | Customer Relationships [Member]
Finite Lived Intangible Assets Net [Abstract]
Business Acquisition Purchase Price Allocation Amortizable Intangible Assets														52
Acquired Finite Lived Intangible Asset Weighted Average Useful Life (in Years)															10
Wholesale Services [Member]
Revenues And Earnings Of Business Acquisition [Abstract]
Revenues															98	121	121
Goodwill RollForward
Goodwill	2	2				0				0					2	0	0
Goodwill Acquired During Period														2
Midstream Operations [Member]
Revenues And Earnings Of Business Acquisition [Abstract]
Revenues															70	46	22
Goodwill RollForward
Goodwill	16	16				14				14					16	14	14
Goodwill Acquired During Period														2
Cargo Shipping [Member]
Revenues And Earnings Of Business Acquisition [Abstract]
Revenues															19	0	0
Goodwill RollForward
Goodwill	77	77				0				0					77	0	0
Goodwill Acquired During Period														77
Cargo Shipping [Member] | Trade Names [Member]
Finite Lived Intangible Assets Net [Abstract]
Business Acquisition Purchase Price Allocation Amortizable Intangible Assets														15
Acquired Finite Lived Intangible Asset Weighted Average Useful Life (in Years)															15
Cargo Shipping [Member] | Customer Relationships [Member]
Finite Lived Intangible Assets Net [Abstract]
Business Acquisition Purchase Price Allocation Amortizable Intangible Assets														$ 3
Acquired Finite Lived Intangible Asset Weighted Average Useful Life (in Years)		18