Equity - Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
CONSOLIDATED STATEMENTS of COMPREHENSIVE INCOME
Net income	$ (74)	$ 293	$ 178	$ 185	$ 128	$ 365	$ 180	$ 190	$ 582	$ 863	$ 761
Reclassification adjustments included in net income
Change in cash flow hedges, net of tax									8	6	6
Change in unrecognized items for pension and other postretirement benefits, net of tax									5	3	4
Net unrealized (losses) gains on cash flow hedges, net of tax									(87)	(34)	16
Net unrecognized items on pension and other postretirement benefits, net of tax									34	(13)	2
Other, net of tax											1
Other comprehensive loss									(40)	(38)	29
Comprehensive income									542	825	790
Comprehensive (income) loss attributable to noncontrolling interests									(7)	(7)	(4)
Comprehensive income attributable to controlling interests									535	818	786
Tax information [Details]
Change in cash flow hedges, tax benefit (expense)									(5)	(4)	(4)
Change in unrecognized items for pension and other postretirement benefits, tax benefit (expense)									(3)	(2)	(3)
Net unrealized gains (losses) on cash flow hedges, tax (expense) benefit									56	22	(10)
Net unrecognized items on pension and other postretirement benefits, tax benefit (expense)									$ (24)	$ 8	$ (1)