Quarterly Financial Data (Unaudited) - (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	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, 2011	Dec. 31, 2010	Dec. 31, 2009
Selected Quarterly Financial Information [Abstract]
Operating revenues	$ 1,737	$ 2,747	$ 2,256	$ 2,167	$ 2,321	$ 2,962	$ 2,372	$ 2,535	$ 8,907	$ 10,190	$ 9,885
Operating income	19	690	428	451	367	753	440	494	1,588	2,054	1,772
Income from continuing operations	(73)	293	180	187	130	365	181	191	587	867	840
Net income	(74)	293	178	185	128	365	180	190	582	863	761
Net income attributable to controlling interests	(76)	291	176	184	125	361	180	190	575	856	757
Basic and diluted earnings per common share
Income from continuing operations attributable to controlling interests, net of tax	$ (0.25)	$ 0.98	$ 0.60	$ 0.63	$ 0.43	$ 1.23	$ 0.62	$ 0.67	$ 1.96	$ 2.96	$ 2.99
Net income attributable to controlling interests	$ (0.25)	$ 0.98	$ 0.60	$ 0.62	$ 0.42	$ 1.23	$ 0.62	$ 0.67	$ 1.94	$ 2.95	$ 2.71
Dividends declared per common share	$ 0.259	$ 0.620	$ 0.620	$ 0.620	$ 0.620	$ 0.620	$ 0.620	$ 0.620	$ 2.119	$ 2.480	$ 2.480
Market price per share - high	$ 56.33	$ 52.42	$ 49.03	$ 46.83	$ 45.61	$ 44.82	$ 40.69	$ 41.35
Market price per share - low	$ 49.37	$ 42.05	$ 45.20	$ 42.55	$ 43.08	$ 38.96	$ 37.13	$ 37.04
CVO mark-to-market, net of tax		50							45	0	(19)
Refund to customers recorded as a reduction to revenue	$ 288