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	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 29		$ 3
Included in Earnings	(56)		10
Included in Regulatory Assets and Liabilities	(14)		42
Purchases	6		10
Issuances
Sales
Settlements	39		4
Transfers In/Out of Level 3	(97)		(5)
Ending Balance	(93)		64
Commodity [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	(62)		(88)
Included in Earnings	(58)		9
Included in Regulatory Assets and Liabilities	(17)		40
Purchases	6		10
Issuances
Sales
Settlements	38		3
Transfers In/Out of Level 3			(5)
Ending Balance	(93)		(31)
Interest Rate Contract [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	(8)		(10)
Included in Earnings	(1)		(1)
Issuances
Sales
Settlements	1		1
Transfers In/Out of Level 3	8
Ending Balance			(10)
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	99	[1]	101	[1]
Included in Earnings	3	[1]	2	[1]
Included in Regulatory Assets and Liabilities	3	[1]	2	[1]
Issuances				[1]
Sales				[1]
Transfers In/Out of Level 3	(105)	[1]
Ending Balance			$ 105	[1]

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