Business Acquisitions and Dispositions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended										3 Months Ended							9 Months Ended	3 Months Ended				9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Sep. 30, 2011 CVSR Financing Agreement [Member]	Sep. 30, 2011 Agua Caliente Financing Agreement [Member]	Aug. 05, 2011 Agua Caliente Financing Agreement [Member]	Sep. 30, 2011 Ivanpah Credit Agreement	Apr. 05, 2011 Ivanpah Credit Agreement	Aug. 23, 2011 West Holdings Credit Agreement Tranche A [Member]	Sep. 30, 2011 Energy Plus [Member]	Sep. 30, 2011 Ivanpah Solar Electric Generating System year	Apr. 05, 2011 Ivanpah Solar Electric Generating System mw	Sep. 30, 2011 Ivanpah Solar Electric Generating System, Facility 1 mw	Sep. 30, 2011 Ivanpah Solar Electric Generating System, Facility 2 mw	Sep. 30, 2011 Ivanpah Solar Electric Generating System, Facility 3 mw	Nov. 05, 2010 Green Mountain Energy	Nov. 15, 2010 Cottonwood mw	Sep. 30, 2011 Solar Facilities [Member]	Sep. 30, 2011 California Valley Solar Ranch [Member] year mw	Sep. 30, 2011 Agua Caliente [Member] year	Aug. 05, 2011 Agua Caliente [Member] mw	Aug. 04, 2011 Agua Caliente [Member]	Sep. 30, 2010 Padoma
Business Acquisitions and Dispositions
Business Acquisition, Customers Acquired												180,000
Total Purchase Price																			$ 507
Number Of Facilities			3																	3
Percentage of ownership interest acquired (as a percent)														50.10%							100.00%			100.00%
Generation capacity (in MW)														392	126	133	133		1,265		250		290
Business Acquisition, Minority partner Additional Equity Commitment																				96
Project financing, amount borrowed							108		626		480
Term of power purchase agreements, low end of the range (in years)													20
Term of power purchase agreements, high end of the range (in years)													25
Line of Credit Facility, Maximum Borrowing Capacity						1,200	967	967	1,627	1,600
Business Acquisition, Purchase Price Allocation [Abstract]
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment																				575
Business Acquisition, Purchase Price Allocation, Restricted Cash																				25
Business Acquisition, Purchase Price Allocation, Current Liabilities, Accrued Liabilities																				364
Business Acquisition, Purchase Price Allocation, Amortizable Intangible Assets																				48
Business Acquisition, Purchase Price Allocation, Current Liabilities, Long-term Debt																				4
Business Acquisition, Purchase Price Allocation, Liabilities Assumed																				368
Business Acquisition, Purchase Price Allocation, Noncontrolling Interest																				154
Business Acquisition, Purchase price Allocation, Other Current adn Noncurrent Assets																				39
Power Purchase Agreement Period																					25	25
Cost of acquired entity, net of cash												193						357		165
Business Acquisition, Purchase Price Allocation, Current Assets, Cash and Cash Equivalents												5						75
Business Acquisition, Restricted Cash Contributed to Project																				291
Business Acquisition, Letters of Credit Contributed to Project																				934
Restricted cash	441		441		8															49
Gain on sale of other disposition	0	0	0	23																					23
Business Acquisition, Purchase Price Allocation, Assets Acquired																				687
Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net																				$ 165