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	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 71		$ (19)		$ 3		$ 22
Included in Earnings	(31)		(34)		(8)		(70)
Included in Regulatory Assets and Liabilities	7		(10)		54		(53)
Purchases	8		1		22		2
Issuances
Sales
Settlements	5		4		(16)		18
Transfers In/Out of Level 3	24		(2)		29		21
Ending Balance	84		(60)		84		(60)
Commodity [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	(25)		(101)		(88)		(59)
Included in Earnings	(27)		(34)		(5)		(68)
Included in Regulatory Assets and Liabilities	9		(12)		54		(56)
Purchases	8		1		22		2
Issuances
Sales
Settlements	4		4		(19)		16
Transfers In/Out of Level 3	24		(2)		29		21
Ending Balance	(7)		(144)		(7)		(144)
Fair Value Interest Rate Contract [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	(10)		(12)		(10)		(11)
Included in Earnings	(1)				(3)		(2)
Included in Regulatory Assets and Liabilities	1				1		(1)
Issuances
Sales
Settlements	1				3		2
Ending Balance	(9)		(12)		(9)		(12)
Fair Value Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	106	[1]	94	[1]	101	[1]	92	[1]
Included in Earnings	(3)	[1]
Included in Regulatory Assets and Liabilities	(3)	[1]	2	[1]	(1)	[1]	4	[1]
Issuances		[1]		[1]		[1]		[1]
Sales		[1]		[1]		[1]		[1]
Ending Balance	$ 100	[1]	$ 96	[1]	$ 100	[1]	$ 96	[1]

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