Fair Value (Details Textuals) (USD $)	3 Months Ended
	Mar. 31, 2012 years	Mar. 31, 2011	Dec. 31, 2011 years
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	$ 103,000,000		$ 111,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	(27,000,000)	(2,000,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	2,000,000	22,000,000
Fair Value, Level 1 to level 2 Transfers, Amount	0	0
Average Maturity of Debt Securities	7		7
Unrealized losses recognized as regulatory assets	47,000,000		67,000,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	0	0
Fair Value of Cash Equivalents Included in Restricted Cash	53,000,000		124,000,000
Fair Value of Cash Equivalents Included in Other Investments	15,000,000		16,000,000
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	0	0
Trading Securities, Change in Unrealized Holding Gain (Loss)	7,000,000	3,000,000
Cash Equivalents [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Available-for-sale Securities, Fair Value Disclosure	68,000,000		140,000,000
Commodity Contract [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	(27,000,000)	(2,000,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	25,000,000
Commodity [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	2,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3		$ 3,000,000