Equity - Comprehensive Income (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Statement of comprehensive income [Details]
Net income	$ 293	$ 365	$ 656	$ 735
Reclassification adjustments included in net income
Change in cash flow hedges, net of tax	2	1	5	4
Change in unrecognized items for pension and other postretirement benefits, net of tax	2	1	4	3
Net unrealized losses on cash flow hedges, net of tax	(69)	(30)	(83)	(80)
Net unrecognized items on pension and other postretirement benefits, net of tax		(4)	(8)	(4)
Other, net of tax		(1)
Other comprehensive loss	(65)	(33)	(82)	(77)
Comprehensive income	228	332	574	658
Comprehensive income attributable to noncontrolling interests	(2)	(4)	(5)	(4)
Comprehensive income attributable to controlling interests	226	328	569	654
Tax information [Details]
Change in cash flow hedges, tax benefit (expense)	(1)	(1)	(3)	(3)
Change in unrecognized items for pension and other postretirement benefits, tax benefit (expense)	(1)		(3)	(1)
Net unrealized gains (losses) on cash flow hedges, tax (expense) benefit	44	19	53	51
Net unrecognized items on pension and other postretirement benefits, tax benefit (expense)		$ 2	$ 5	$ 2