Fair Value Of Financial Assets And Liabilities (Reconciliation Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs) (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010	Sep. 30, 2011		Sep. 30, 2010
Beginning balance	$ 121,000,000		$ 219,000,000	$ 146,000,000		$ 223,000,000
Fuel used in electric generation and purchased power-non-regulated, fair value						(14,000,000)
Gains (losses) on available for sale securities and other	8,000,000		2,000,000	13,000,000		12,000,000
Purchases	8,000,000	[1]		15,000,000	[1]
Sales				(3,000,000)
Settlements	(3,000,000)			(30,000,000)
Net purchases, sales, issuances and settlements			(5,000,000)			6,000,000
Total gains included on the Condensed Consolidated Balance Sheet as regulatory asset or liability	(15,000,000)		3,000,000	6,000,000		18,000,000
Transfers out of Level 3	(25,000,000)			(34,000,000)
Ending Balance	102,000,000		201,000,000	102,000,000		201,000,000
Pre-tax revenue, non-regulated electric, natural gas, and other				(12,000,000)
Pre-tax fuel used in electric generation and purchased power-non-regulated			(3,000,000)
Total				(12,000,000)
Regulated Operation [Member]
Revenue, non-regulated electric, natural gas, and other	8,000,000	[1]		8,000,000	[1]
Regulated Operation [Member] | Derivatives, Net [Member]
Revenue, non-regulated electric, natural gas, and other	8,000,000	[1]		8,000,000.00	[1]
Unregulated Operation [Member]
Revenue, non-regulated electric, natural gas, and other				(19,000,000)		(44,000,000)
Pre-tax revenue, non-regulated electric, natural gas, and other			(15,000,000)
Unregulated Operation [Member] | Derivatives, Net [Member]
Revenue, non-regulated electric, natural gas, and other				(19,000,000.00)		(44,000,000.00)
Pre-tax revenue, non-regulated electric, natural gas, and other			(15,000,000.00)
Available-For-Sale Auction Rate Securities [Member]
Beginning balance	90,000,000		178,000,000	118,000,000.00		198,000,000.00
Gains (losses) on available for sale securities and other	8,000,000		2,000,000.00	13,000,000.00		12,000,000.00
Settlements	(1,000,000)			(25,000,000.00)
Net purchases, sales, issuances and settlements			(3,000,000.00)			(33,000,000.00)
Transfers out of Level 3	(25,000,000)			(34,000,000.00)
Ending Balance	72,000,000		177,000,000.00	72,000,000		177,000,000.00
Available-For-Sale NDTF Investments [Member]
Beginning balance	53,000,000		48,000,000	47,000,000.00
Purchases				7,000,000.00	[1]
Sales				(3,000,000.00)
Net purchases, sales, issuances and settlements			(4,000,000.00)			44,000,000.00
Total gains included on the Condensed Consolidated Balance Sheet as regulatory asset or liability	1,000,000		2,000,000.00	3,000,000.00		2,000,000.00
Ending Balance	54,000,000.00		46,000,000.00	54,000,000.00		46,000,000.00
Derivatives, Net [Member]
Beginning balance	(22,000,000)		(7,000,000)	(19,000,000.00)		25,000,000.00
Fuel used in electric generation and purchased power-non-regulated, fair value						(14,000,000.00)
Purchases	8,000,000	[1]		8,000,000.00	[1]
Settlements	(2,000,000)			(5,000,000.00)
Net purchases, sales, issuances and settlements			2,000,000.00			(5,000,000.00)
Total gains included on the Condensed Consolidated Balance Sheet as regulatory asset or liability	(16,000,000)		1,000,000.00	3,000,000.00		16,000,000.00
Ending Balance	(24,000,000.00)		(22,000,000.00)	(24,000,000.00)		(22,000,000.00)
Pre-tax revenue, non-regulated electric, natural gas, and other				(12,000,000.00)
Pre-tax fuel used in electric generation and purchased power-non-regulated			(3,000,000.00)
Total				$ (12,000,000.00)

[1] Derivative amounts relate to financial transmission rights.