Equity - Comprehensive Income (Details) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Statement of comprehensive income [Details]
Net income	$ 178	$ 180	$ 363	$ 370
Reclassification adjustments included in net income
Change in cash flow hedges, net of tax	2	2	3	3
Change in unrecognized items for pension and other postretirement benefits, net of tax	1	1	2	2
Net unrealized losses on cash flow hedges, net of tax	(16)	(44)	(14)	(50)
Net unrecognized items on pension and other postretirement benefits, net of tax	(8)	0	(8)	0
Other, net of tax	0	1	0	1
Other comprehensive loss	(21)	(40)	(17)	(44)
Comprehensive income	157	140	346	326
Comprehensive income attributable to noncontrolling interests	(2)	0	(3)	0
Comprehensive income attributable to controlling interests	155	140	343	326
Tax information [Details]
Change in cash flow hedges, tax benefit (expense)	(1)	(1)	(2)	(2)
Change in unrecognized items for pension and other postretirement benefits, tax benefit (expense)	(1)	0	(2)	(1)
Net unrealized gains (losses) on cash flow hedges, tax (expense) benefit	10	28	9	32
Net unrecognized items on pension and other postretirement benefits, tax benefit (expense)	5	0	5	0
Other, tax	$ 0	$ 0	$ 0	$ 0