Fair Value (Details Textuals) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012 years	Sep. 30, 2011	Sep. 30, 2012 years	Sep. 30, 2011	Dec. 31, 2011 years
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	$ 106		$ 106		$ 95
Average Maturity of Debt Securities	6		6		7
Unrealized losses recognized as regulatory assets	56		56		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	55		55		124
Fair Value of Cash Equivalents Included in Other Investments	14		14		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)			9	(3)
Cash Equivalents [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Available-for-sale Securities, Fair Value Disclosure	69		69		140
Equity [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Available-for-sale Securities, Fair Value Disclosure	$ 6		$ 6		$ 5