Note 2 - Significant Accounting Policies and Methods of Application (Detail) - Potentially Dilutive Common Share Calculation (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Net income attributable to AGL Resources Inc. (in Dollars)	$ 154		$ 130
Basic weighted average number of shares outstanding (1)	117.4	[1]	116.7	[1]
Effect of dilutive securities	0.3		0.3
Diluted weighted average number of shares outstanding	117.7		117.0
Basic (in Dollars per share)	$ 1.31		$ 1.12
Diluted (in Dollars per share)	$ 1.31		$ 1.11

[1] Daily weighted average shares outstanding.