Nuclear Decommissioning Trust Fund Investments (Proceeds From The Sale Of Investments And Related Gross Realized Gains And Losses In Nuclear Decommissioning Trust Fund) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Nuclear Decommissioning Trust Fund Investments [Line Items]
Proceeds from sales	$ 199	$ 256	$ 380
Gross realized gains	5	5	5
Gross realized losses	$ 4	$ 4	$ 10
Minimum [Member] | Nuclear Decommissioning Trust Fund [Member]
Nuclear Decommissioning Trust Fund Investments [Line Items]
Trust fund investments, target allocation percentage	60.00%
Maximum [Member] | Nuclear Decommissioning Trust Fund [Member]
Nuclear Decommissioning Trust Fund Investments [Line Items]
Trust fund investments, target allocation percentage	70.00%