Nuclear Decommissioning Trust Fund Investments (Fair Value And The Gross Unrealized Losses Of The Available-For-Sale Securities Held In Nuclear Decommissioning Trust Fund) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Nuclear Decommissioning Trust Fund Investments [Line Items]
Less than 12 months, fair value	$ 25
Less than 12 months, gross unrealized losses	4
12 months or greater, fair value	8
12 months or greater, gross unrealized losses	8
Total, fair value	33
Total, gross unrealized losses	12
Debt Securities [Member]
Nuclear Decommissioning Trust Fund Investments [Line Items]
Less than 12 months, fair value	7
Total, fair value	7
Equity Securities [Member]
Nuclear Decommissioning Trust Fund Investments [Line Items]
Less than 12 months, fair value	18
Less than 12 months, gross unrealized losses	4
12 months or greater, fair value	8
12 months or greater, gross unrealized losses	8
Total, fair value	26
Total, gross unrealized losses	$ 12