Fair Value (Details Textuals) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012 years	Jun. 30, 2011	Jun. 30, 2012 years	Jun. 30, 2011	Dec. 31, 2011 years
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	$ 102		$ 102		$ 95
Average Maturity of Debt Securities	7		7		7
Unrealized losses recognized as regulatory assets	65		65		67
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	0	0	0	0
Fair Value of Cash Equivalents Included in Restricted Cash	99		99		124
Fair Value of Cash Equivalents Included in Other Investments	16		16		16
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	0	0	0	0
Trading Securities, Change in Unrealized Holding Gain (Loss)			5	4
Cash Equivalents [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Available-for-sale Securities, Fair Value Disclosure	$ 115		$ 115		$ 140