Investments (Investments Under Equity Method of Accounting) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Investment Balance	$ 553	$ 571
Iroquois Gas Transmission System, LP [Member]
Ownership %	24.72%
Investment Balance	104	106
Description	Gas transmission system
Elwood Energy LLC [Member]
Ownership %	50.00%
Investment Balance	108	98
Description	Natural gas-fired merchant generation peaking facility
Fowler I Holdings LLC [Member]
Ownership %	50.00%
Investment Balance	166	180
Description	Wind-powered merchant generation facility
NedPower Mount Storm LLC [Member]
Ownership %	50.00%
Investment Balance	146	149
Description	Wind-powered merchant generation facility
Other Investment [Member]
Investment Balance	$ 29	$ 38