Fair Value (Details Textuals) (USD $)	12 Months Ended
	Dec. 31, 2011 years	Dec. 31, 2010 years	Dec. 31, 2009
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	$ 111,000,000	$ 111,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	(24,000,000)	35,000,000
Transfers into Level 3	4,000,000	9,000,000
Fair Value, Level 1 to level 2 Transfers, Amount	0	0
Average Maturity of Debt Securities	7	6
Unrealized losses recognized as regulatory assets	67,000,000	26,000,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	0	0	0
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)	3,000,000	7,000,000	8,000,000
Publicly Traded Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Nuclear Decommissioning Trust Fund Investments	57.00%	61.00%
Fixed Income Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Nuclear Decommissioning Trust Fund Investments	41.00%	38.00%
Cash Equivalents [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Nuclear Decommissioning Trust Fund Investments	2.00%	1.00%
Fair Value, Measurements, Recurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	$ 25,000,000