Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
Operating revenues (includes revenue taxes of $9 and $83 for the three and nine months in 2015, respectively, and $9 and $103 for the three and nine months in 2014, respectively)	$ 584	$ 589	$ 2,979	$ 3,940
Operating expenses
Cost of goods sold	146	198	1,303	2,000
Operation and maintenance	204	193	662	693
Depreciation and amortization	98	93	293	281
Taxes other than income taxes	28	30	142	160
Merger-related expenses	35	0	35	0
Goodwill impairment	14	0	14	0
Total operating expenses	525	514	2,449	3,134
Gain on disposition of assets	0	3	0	3
Operating income	59	78	530	809
Other income	2	3	9	8
Interest expense, net	(42)	(44)	(128)	(135)
Income before income taxes	19	37	411	682
Income tax expense	7	14	150	254
Income from continuing operations	12	23	261	428
Loss from discontinued operations, net of tax	0	(31)	0	(80)
Net income (loss)	12	(8)	261	348
Less net income attributable to noncontrolling interest	1	0	15	14
Net income (loss) attributable to AGL Resources	11	(8)	246	334
Net income (loss) attributable to AGL Resources
Income from continuing operations	11	23	246	414
Loss from discontinued operations, net of tax	0	(31)	0	(80)
Net income (loss) attributable to AGL Resources	$ 11	$ (8)	$ 246	$ 334
Basic earnings (loss) per common share
Continuing operations (in dollars per share)	$ 0.09	$ 0.19	$ 2.06	$ 3.48
Discontinued operations (in dollars per share)	0.00	(0.25)	0.00	(0.67)
Basic earnings (loss) per common share attributable to AGL Resources Inc. (in dollars per share)	0.09	(0.06)	2.06	2.81
Diluted earnings (loss) per common share
Continuing operations (in dollars per share)	0.09	0.19	2.05	3.47
Discontinued operations (in dollars per share)	0.00	(0.25)	0.00	(0.67)
Diluted earnings (loss) per common share attributable to AGL Resources Inc. (in dollars per share)	0.09	(0.06)	2.05	2.80
Cash dividends declared per common share (in dollars per share)	$ 0.51	$ 0.49	$ 1.53	$ 1.47
Weighted average number of common shares outstanding
Basic (in shares)	119.6	119.0	119.5	118.8
Diluted (in shares)	120.0	119.4	119.8	119.2