Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Operating revenues (includes revenue taxes of $103 for 2015, $133 for 2014 and $112 for 2013, respectively)	$ 3,941	$ 5,385	$ 4,209
Operating expenses
Cost of goods sold	1,645	2,765	2,110
Operation and maintenance	914	939	887
Depreciation and amortization	397	380	397
Taxes other than income taxes	181	208	187
Merger-related expenses	44	0	0
Goodwill impairment	14	0	0
Total operating expenses	3,195	4,292	3,581
Gain on disposition of assets	0	2	11
Operating income	746	1,095	639
Other income	13	14	16
Interest expense, net	(173)	(179)	(170)
Income before income taxes	586	930	485
Income tax expense	213	350	177
Income from continuing operations	373	580	308
(Loss) income from discontinued operations, net of tax	0	(80)	5
Net income	373	500	313
Less net income attributable to the noncontrolling interest	20	18	18
Net income attributable to AGL Resources	353	482	295
Net income attributable to AGL Resources
Income from continuing operations attributable to AGL Resources	353	562	290
(Loss) income from discontinued operations, net of tax	0	(80)	5
Net income attributable to AGL Resources	$ 353	$ 482	$ 295
Basic earnings (loss) per common share
Continuing operations (in dollars per share)	$ 2.95	$ 4.73	$ 2.46
Discontinued operations (in dollars per share)	0.00	(0.67)	0.04
Basic earnings per common share attributable to AGL Resources Inc. common shareholders (in dollars per share)	2.95	4.06	2.50
Diluted earnings (loss) per common share
Continuing operations (in dollars per share)	2.94	4.71	2.45
Discontinued operations (in dollars per share)	0.00	(0.67)	0.04
Diluted earnings per common share attributable to AGL Resources Inc. common shareholders (in dollars per share)	2.94	4.04	2.49
Cash dividends declared per common share (in dollars per share)	$ 2.04	$ 1.96	$ 1.88
Weighted average number of common shares outstanding
Basic (in shares)	119.6	118.8	117.9
Diluted (in shares)	119.9	119.2	118.3