Fair Value (Details Textuals) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011 banks customers years ratio employees	Sep. 30, 2010	Sep. 30, 2011 percent people years kWh Days weeks MCF banks customers ratio employees	Sep. 30, 2010	Dec. 31, 2010 years
Fair Value, Option, Quantitative Disclosures [Line Items]
Average Maturity of Debt Securities	7		7		6
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax			$ 0	$ 0
Unrealized losses recognized as regulatory assets	87,000,000		87,000,000		26,000,000
Trading Securities, Change in Unrealized Holding Gain (Loss)			(3,000,000)	3,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	(42,000,000)		(24,000,000)
Other investments	104,000,000		104,000,000		111,000,000
Fair Value, Level 1 to level 2 Transfers, Amount	0	0	0	0
Transfers into Level 3	(7,000,000)		(4,000,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net		(22,000,000)		52,000,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	$ 0	$ 0	$ 0	$ 0