Other Impairments and Restructuring (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 years	Dec. 31, 2010	Dec. 31, 2009	Jun. 30, 2010
Restructuring Cost and Reserve [Line Items]
Asset Impairment Charges	$ 1	$ 10	$ 6
Amortization Period of CTA	10
Pre Tax Amount of Cost To Achieve Previously Expensed Deferred and Recognized in Income				32
After Tax Amount of Cost To Achieve Previously Expensed deferred and Recognized in Income				20
Non Pension Component of Cost To Achieve Included in Regulatory Assets				21
Pension Componenet of Costs to Achieve Included in Regulatory Liabilities				11
Electric Utility [Member]
Restructuring Cost and Reserve [Line Items]
Amortization of Deferred Cost to Achieve	18	18	18
Gas Utility [Member]
Restructuring Cost and Reserve [Line Items]
Amortization of Deferred Cost to Achieve	$ 3	$ 2