Nuclear Decommissioning Trust Fund Investments (Fair Values Of Investments In Debt And Equity Securities In Nuclear Decommissioning Trust Fund) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Nuclear Decommissioning Trust Fund Investments [Line Items]
Cost	$ 261		$ 247
Gross unrealized gains	108		99
Gross unrealized loss	12		9
Fair value	357		337
Debt Securities [Member]
Nuclear Decommissioning Trust Fund Investments [Line Items]
Cost	114		104
Gross unrealized gains	7		4
Gross unrealized loss			1
Fair value	121		107
Equity Securities [Member]
Nuclear Decommissioning Trust Fund Investments [Line Items]
Cost	145		141
Gross unrealized gains	101		95
Gross unrealized loss	12		8
Fair value	234		228
Cash [Member]
Nuclear Decommissioning Trust Fund Investments [Line Items]
Cost	3		1
Fair value	3		1
Other Debt And Equity Securities [Member]
Nuclear Decommissioning Trust Fund Investments [Line Items]
Cost	(1)	[1]	1	[1]
Fair value	$ (1)	[1]	$ 1	[1]

[1] Represents payables relating to pending security purchases, net of receivables related to pending securities sales and interest receivables.