Note 2 - Significant Accounting Policies and Methods of Application (Details) - Potentially Dilutive Common Share Calculation (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Potentially Dilutive Common Share Calculation [Abstract]
Net income attributable to AGL Resources Inc. (in Dollars)	$ 49		$ 34		$ 203		$ 164
Denominator:
Basic weighted average number of shares outstanding (1)	117.8	[1]	116.9	[1]	117.6	[1]	116.8	[1]
Effect of dilutive securities	0.4		0.3		0.3		0.3
Diluted weighted average number of shares outstanding	118.2		117.2		117.9		117.1
Basic (in Dollars per share)	$ 0.41		$ 0.28		$ 1.72		$ 1.40
Diluted (in Dollars per share)	$ 0.41		$ 0.28		$ 1.72		$ 1.40

[1] Daily weighted average shares outstanding.