Consolidated Statements of Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Statement [Abstract]
Operating revenue	$ 10,577	$ 9,983	$ 9,965
Fuel	367	363	721
Purchased power	2,989	2,930	2,751
Operation and maintenance	3,387	3,291	3,154
Depreciation, decommissioning and amortization	1,426	1,273	1,178
Property and other taxes	285	263	244
Gain on sale of assets	0	(1)	(1)
Total operating expenses	8,454	8,119	8,047
Operating income	2,123	1,864	1,918
Interest income	5	7	11
Other income	135	141	160
Interest expense	(463)	(429)	(420)
Other expenses	(55)	(51)	(49)
Income before income taxes	1,745	1,532	1,620
Income tax expense	601	440	249
Net income	1,144	1,092	1,371
Less: Net income attributable to noncontrolling interests	0	0	94
Dividends on preferred and preference stock	59	52	51
Net income available for common stock	$ 1,085	$ 1,040	$ 1,226