Fair Value Measurements (Gains and Losses Included in Earnings in the Level 3 Fair Value Category) (Details) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Total gains (losses) included in earnings	$ (22)	$ 12	$ (8)	$ 13
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) relating to assets/liabilities still held at the reporting date	27	3	31	(11)
Operating Revenue [Member]
Total gains (losses) included in earnings	2	6		(10)
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) relating to assets/liabilities still held at the reporting date	27	3	31	(9)
Electric Fuel and Other Energy-Related Purchases [Member]
Total gains (losses) included in earnings	(24)	6	(8)	26
Purchased Gas [Member]
Total gains (losses) included in earnings				(3)
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) relating to assets/liabilities still held at the reporting date				$ (2)