Stockholders' Equity (Schedule of Stockholders' Equity) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)
Equity, beginning balance	$ 1,728
Redeemable Noncontrolling Interests, beginning balance	554
Comprehensive income including portion attributable to nonredeemable noncontrolling interests	(319)
Distributions to noncontrolling interests, net of contributions	(14)
Disposition of less-than-wholly owned entity	(13)
Other reclassifications of noncontrolling interests	1
Noncontrolling interests in acquired entity	1
Cancellation of restricted stock for tax withholdings on vested shares	(5)
Stock-based compensation	14
Equity, ending balance	1,393
Redeemable Noncontrolling Interests, ending balance	548
Redeemable Noncontrolling Interests [Member]
Redeemable Noncontrolling Interests, beginning balance	554
Comprehensive income attributable to redeemable noncontrolling interest	29
Contributions from noncontrolling interests	5
Distributions to redeemable noncontrolling interests, net of contributions	(39)
Purchase of subsidiary shares from noncontrolling interests	(4)
Disposition of less-than-wholly owned entity	4
Other reclassifications of redeemable noncontrolling interests	(1)
Equity, ending balance	548
Redeemable Noncontrolling Interests, ending balance
Common Stock [Member]
Equity, beginning balance	1
Equity, ending balance	1
Additional Paid-in Capital [Member]
Equity, beginning balance	1,975
Cancellation of restricted stock for tax withholdings on vested shares	(5)
Stock-based compensation	14
Equity, ending balance	1,984
Accumulated Other Comprehensive Income (Loss) [Member]
Equity, beginning balance	(62)
Comprehensive income including portion attributable to nonredeemable noncontrolling interests	9
Equity, ending balance	(53)
Retained Earnings (Accumulated Deficit) [Member]
Equity, beginning balance	(299)
Comprehensive income including portion attributable to nonredeemable noncontrolling interests	(335)
Equity, ending balance	(634)
Noncontrolling Interests [Member]
Equity, beginning balance	113
Comprehensive income including portion attributable to nonredeemable noncontrolling interests	7
Distributions to noncontrolling interests, net of contributions	(14)
Disposition of less-than-wholly owned entity	(13)
Other reclassifications of noncontrolling interests	1
Noncontrolling interests in acquired entity	1
Equity, ending balance	$ 95