Impairment and Long-Lived Assets Pending Sale (Details Textuals) (USD $)	9 Months Ended			3 Months Ended		3 Months Ended	9 Months Ended			0 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Mar. 31, 2011 Fremont Energy Center	Mar. 11, 2011 Fremont Energy Center mW	Sep. 30, 2011 Peaking Facilities	Sep. 30, 2011 Peaking Facilities	Oct. 18, 2011 Peaking Facilities Discontinued Operation or Asset Disposal [Member] mW	Sep. 30, 2011 Signal Peak	Oct. 18, 2011 Signal Peak Discontinued Operation or Asset Disposal [Member]
Impairment of Long-Lived Assets (Textuals) [Abstract]
Number of gas combined cycle combustion turbines sold					2
Number of steam turbine sold					1
Load following capacity					544
Peaking capacity					163			450
Asset impairments	$ 59,000,000	$ 315,000,000		$ 11,000,000		$ 3,000,000	$ 23,000,000
Joint venture ownership percentage by parent									50.00%
Interest in Joint Venture acquired by a subsidiary of Gunvor Group										33.33%
Equity Method Investment, Ownership Percentage										33.33%
Proceeds from Divestiture of Interest in Consolidated Subsidiaries										257,500,000
Gain (Loss) On Divestiture Net Of Tax										370,000,000
Impact of joint venture on noncontrolling interest	$ (31,000,000)		$ (32,000,000)						$ (50,000,000)