Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended						0 Months Ended							0 Months Ended
	Jun. 30, 2012		Dec. 31, 2011	Feb. 13, 2012 Cedro Hill Project MW	Feb. 13, 2012 Mountain Wind Power I Project MW	Feb. 13, 2012 Mountain Wind Power II Project MW	Feb. 13, 2012 Capistrano Wind Partners	Jun. 30, 2012 Variable Interest Entity, Primary Beneficiary MW projects	Dec. 31, 2011 Variable Interest Entity, Primary Beneficiary projects MW	Feb. 13, 2012 Agreement to Sell Ownership, Upon Satisfaction of Specific Conditions Capistrano Wind Partners	Feb. 13, 2012 Agreement to Sell Ownership, Upon Satisfaction of Specific Conditions Broken Bow I Project MW	Feb. 13, 2012 Agreement to Sell Ownership, Upon Satisfaction of Specific Conditions Crofton Bluffs Project MW	Feb. 13, 2012 Mission Energy Holding Company	Feb. 13, 2012 Mission Energy Holding Company Capistrano Wind Partners
Details of projects or entities
Number of projects consolidated (in projects)								16	13
Total generating capacity (in megawatts)								861	570
Assets serving as collateral for the debt obligations								$ 472	$ 136
Summarized balance sheet information of VIEs
Current assets	1,658		1,941					118	36
Net property, plant and equipment	4,463		4,472					1,107	675
Other long-term assets	1,604		1,387					22	5
Total Assets	8,254		8,323					1,247	716
Current liabilities	925		548					34	28
Long-term debt net of current portion	4,430		4,855					175	57
Deferred revenues	517		530					173	69
Long-term derivative liabilities	114		90					22	0
Other long-term liabilities	606		636					37	22
Total Liabilities	6,592		6,659					441	176
Noncontrolling interests	244		2					244	2
Sale of ownership (in megawatts)				150	61	80					80	40
Outside investors contribution							238			140
Class A equity ownership percentage (as a percent)														100.00%
Preferred equity interests to receive percent of cash available for distribution (as a percent)							100.00%
Cash available for distribution includes percent of tax benefits to be realized (as a percent)							90.00%
Preferred investment made													4
Transfers of assets to Capistrano Wind Partners	$ 21	[1]

[1] Additional paid in capital was reduced by $21 million during the six months ended June 30, 2012 due to a new tax basis in the assets transferred to Capistrano Wind Partners. The tax basis allocation to the transferred assets was updated during the three months ended June 30, 2012. For further information, see Note 3—Variable Interest Entities—Projects or Entities that are Consolidated—Capistrano Wind Equity Capital.