Note 3 - Merger with Nicor (Detail) - Pro Forma Financial Information (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2011	Dec. 31, 2011
Total revenues (in Dollars)	$ 1,915	$ 4,715
Net income attributable to AGL Resources Inc. (in Dollars)	$ 165	$ 313
Basic earnings per common share	$ 1.42	$ 2.69
Diluted earnings per common share	$ 1.42	$ 2.68