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	6 Months Ended		3 Months Ended	6 Months Ended		3 Months Ended	6 Months Ended		3 Months Ended	6 Months Ended		3 Months Ended
	Jun. 30, 2011	Jun. 30, 2011 Energy Commodities, Net [Member] Wholesale Energy Marketing [Member]	Jun. 30, 2011 Energy Commodities, Net [Member] Wholesale Energy Marketing [Member]	Jun. 30, 2010 Energy Commodities, Net [Member] Wholesale Energy Marketing [Member]	Jun. 30, 2011 Energy Commodities, Net [Member] Unregulated Retail Electric and Gas [Member]	Jun. 30, 2011 Energy Commodities, Net [Member] Unregulated Retail Electric and Gas [Member]	Jun. 30, 2010 Energy Commodities, Net [Member] Unregulated Retail Electric and Gas [Member]	Jun. 30, 2011 Energy Commodities, Net [Member] Net Energy Trading Margins [Member]	Jun. 30, 2011 Energy Commodities, Net [Member] Net Energy Trading Margins [Member]	Jun. 30, 2010 Energy Commodities, Net [Member] Net Energy Trading Margins [Member]	Jun. 30, 2011 Energy Commodities, Net [Member] Energy Purchases [Member]	Jun. 30, 2011 Energy Commodities, Net [Member] Energy Purchases [Member]	Jun. 30, 2010 Energy Commodities, Net [Member] Energy Purchases [Member]	Jun. 30, 2010 Wholesale Energy Marketing [Member]	Jun. 30, 2010 Unregulated Retail Electric and Gas [Member]	Jun. 30, 2010 Net Energy Trading Margins [Member]	Jun. 30, 2010 Energy Purchases [Member]
Net gains and losses on assets and liabilities
Total gains (losses) included in earnings for the period		$ (5)	$ (4)	$ 13	$ 4	$ 5	$ 12	$ 2	$ (3)	$ (2)	$ (6)	$ (2)	$ (91)	$ 0	$ 1	$ (3)	$ (5)
Change in unrealized gains (losses) relating to positions still held at the reporting date		$ (7)	$ (6)	$ 5	$ 4	$ 5	$ 10	$ 0	$ 0	$ (3)	$ (2)	$ 17	$ (81)	$ 0	$ (1)	$ (2)	$ (6)
Recurring Fair Value Measurements Valuation Techniques - NDT Funds (Numeric)
Percentage of Wilshire 5000 Index invested in large-cap stocks (in hundredths)	70.00%
Percentage of Wilshire 5000 Index invested in mid/small-cap stocks (in hundredths)	30.00%
Weighted average coupon of NDT funds debt securities (in hundredths)	4.55%
Weighted average duration of debt securities (in years)	5
Recurring Fair Value Measurements Valuation Techniques - Auction Rate Securities (Numeric)
Weighted average contractual maturity of auction rate securites (in years)	24