Fair Value Measurements (Reconciliation Of The Beginning And Ending Net Balances For Assets And Liabilities Measured At Level 3 Fair Value) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 3		$ 22
Included in Earnings	(116)		(131)
Included in Regulatory Assets and Liabilities	20		24
Purchases	32		5
Settlements	70		110
Transfers In/Out of Level 3	20		(27)
Ending Balance	29		3
Commodity [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	(88)		(59)
Included in Earnings	(113)		(131)
Included in Regulatory Assets and Liabilities	20		17
Purchases	32		5
Settlements	67		107
Transfers In/Out of Level 3	20		(27)
Ending Balance	(62)		(88)
Fair Value Interest Rate Contract [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	(10)		(11)
Included in Earnings	(3)		(3)
Included in Regulatory Assets and Liabilities	2		1
Settlements	3		3
Ending Balance	(8)		(10)
Fair Value Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	101	[1]	92	[1]
Included in Earnings			3	[1]
Included in Regulatory Assets and Liabilities	(2)	[1]	6	[1]
Ending Balance	$ 99	[1]	$ 101	[1]

[1] Amounts included in earnings are reported in investment and other income on the consolidated income statement.