Quarterly Finanical Information (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	1 Months Ended	3 Months Ended												12 Months Ended
	Dec. 31, 2011	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Sep. 30, 2009	Jun. 30, 2009	Mar. 31, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Selected Quarterly Financial Information Abstract
Revenues	$ 209	$ 790	$ 295	$ 375	$ 878	$ 665	$ 346	$ 359	$ 1,003	$ 638	$ 307	$ 377	$ 995	$ 2,338	$ 2,373	$ 2,317
Operating Income Loss		118	24	60	238	137	62	48	253	148	43	55	230	440	500	476
Net Income Loss		$ 33	$ (3)	$ 18	$ 124	$ 64	$ 22	$ 14	$ 134	$ 71	$ 12	$ 20	$ 119	$ 172	$ 234	$ 222
Basic earnings (loss) per common share attributable to AGL Resources Inc. common shareholders	$ (0.30)	$ 0.37	$ (0.04)	$ 0.23	$ 1.60	$ 0.82	$ 0.29	$ 0.17	$ 1.74	$ 0.92	$ 0.16	$ 0.26	$ 1.55	$ 2.14	$ 3.02	$ 2.89
Diluted earnings (loss) per common share attributable to AGL Resources Inc. common shareholders	$ (0.30)	$ 0.37	$ (0.04)	$ 0.23	$ 1.59	$ 0.81	$ 0.29	$ 0.17	$ 1.73	$ 0.92	$ 0.16	$ 0.26	$ 1.55	$ 2.12	$ 3.00	$ 2.88