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, 2012		Mar. 31, 2011
Net income attributable to AGL Resources Inc. (in Dollars)	$ 130		$ 124
Basic weighted average number of shares outstanding (1)	116.7	[1]	77.7	[1]
Effect of dilutive securities	0.3		0.3
Diluted weighted average number of shares outstanding	117.0		78.0
Basic and diluted earnings per share
Basic (in Dollars per share)	$ 1.12		$ 1.60
Diluted (in Dollars per share)	$ 1.11		$ 1.59

[1] Daily weighted average shares outstanding.