Fair Value Measurements and Credit Concentration (Net Asset and Liability Measured on Recurring Basis Level 3 Gain Loss Included in Earnings and Other Recurring Numeric Data) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Net gains and losses on assets and liabilities [Abstract]
Total gains (losses) included in earnings for the period			$ (2)	$ (163)
Change in unrealized gains (losses) relating to positions still held at the reporting date			20	(5)
Recurring Fair Value Measurements Valuation Techniques - NDT Funds (Numeric) [Abstract]
Percentage of Wilshire 5000 Index invested in large-cap stocks (in hundredths)	70.00%		70.00%
Percentage of Wilshire 5000 Index invested in mid/small-cap stocks (in hundredths)	30.00%		30.00%
Weighted average coupon of NDT funds debt securities (in hundredths)	4.53%		4.53%
Weighted average duration of debt securities (in years)	5		5
Recurring Fair Value Measurements Valuation Techniques - Auction Rate Securities (Numeric) [Abstract]
Weighted average contractual maturity of auction rate securites (in years)	24		24
Energy Commodities, Net [Member] | Wholesale Energy Marketing [Member]
Net gains and losses on assets and liabilities [Abstract]
Total gains (losses) included in earnings for the period	(1)	3	(5)	16
Change in unrealized gains (losses) relating to positions still held at the reporting date	0	4	(6)	8
Energy Commodities, Net [Member] | Unregulated Retail Electric and Gas [Member]
Net gains and losses on assets and liabilities [Abstract]
Total gains (losses) included in earnings for the period	6	10	11	22
Change in unrealized gains (losses) relating to positions still held at the reporting date	3	8	6	18
Energy Commodities, Net [Member] | Net Energy Trading Margins [Member]
Net gains and losses on assets and liabilities [Abstract]
Total gains (losses) included in earnings for the period	1	1	(2)	(1)
Change in unrealized gains (losses) relating to positions still held at the reporting date	1	0	1	0
Energy Commodities, Net [Member] | Energy Purchases [Member]
Net gains and losses on assets and liabilities [Abstract]
Total gains (losses) included in earnings for the period	0	(72)
Change in unrealized gains (losses) relating to positions still held at the reporting date	$ 1	$ (3)