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	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Net income attributable to AGL Resources Inc. (in Dollars)	$ 271		$ 172		$ 234
Basic weighted average number of shares outstanding (1)	117.0	[1]	80.4	[1]	77.4	[1]
Effect of dilutive securities	0.5		0.5		0.4
Diluted weighted average number of shares outstanding	117.5		80.9		77.8
Basic (in Dollars per share)	$ 2.32		$ 2.14		$ 3.02
Diluted (in Dollars per share)	$ 2.31		$ 2.12		$ 3.00

[1] Daily weighted average shares outstanding.