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								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Potentially Dilutive Common Share Calculation [Abstract]
Income from continuing operations attributable to AGL Resources Inc. (in Dollars)	$ 148	$ 23	$ 57	$ 334	$ 73	$ 24	$ 44	$ 149	$ 562		$ 290		$ 259
(Loss) income from discontinued operations, net of tax (in Dollars)									(80)		5		1
Net income attributable to AGL Resources Inc. (in Dollars)	$ 148	$ (8)	$ 58	$ 284	$ 77	$ 25	$ 43	$ 150	$ 482		$ 295		$ 260
Basic weighted average number of common shares outstanding (1) (in Shares)									118.8	[1]	117.9	[1]	117.0	[1]
Effect of dilutive securities (in Shares)									0.4		0.4		0.5
Diluted weighted average number of common shares outstanding (2) (in Shares)									119.2	[2]	118.3	[2]	117.5	[2]
Continuing operations	$ 1.24	$ 0.19	$ 0.48	$ 2.82	$ 0.61	$ 0.20	$ 0.38	$ 1.27	$ 4.73		$ 2.46		$ 2.21
Discontinued operations		$ (0.25)	$ 0.01	$ (0.43)	$ 0.03	$ 0.01	$ (0.01)	$ 0.01	$ (0.67)		$ 0.04		$ 0.01
Basic earnings per common share attributable to AGL Resources Inc. common shareholders									$ 4.06		$ 2.50		$ 2.22
Continuing operations	$ 1.24	$ 0.19	$ 0.48	$ 2.81	$ 0.61	$ 0.20	$ 0.38	$ 1.26	$ 4.71	[2]	$ 2.45	[2]	$ 2.20	[2]
Discontinued operations		$ (0.25)	$ 0.01	$ (0.43)	$ 0.03	$ 0.01	$ (0.01)	$ 0.01	$ (0.67)	[2]	$ 0.04	[2]	$ 0.01	[2]
Diluted earnings per common share attributable to AGL Resources Inc. common shareholders									$ 4.04		$ 2.49		$ 2.21

[1] Daily weighted average shares outstanding.

[2] There were no outstanding stock options excluded from the computation of diluted earnings per common share attributable to AGL Resources Inc. for any of the periods presented because their effect would have been anti-dilutive, as the exercise prices were greater than the average market price.