Stockholders' Deficit (Schedule of Stockholders' Deficit) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Equity, beginning balance	$ (1,463)	$ (692)
Redeemable Noncontrolling Interests, beginning balance	504
Comprehensive income (loss)	(110)	(2)
Distributions to noncontrolling interests	(8)	(6)
Purchase of subsidiary shares from noncontrolling interests		(2)
Other reclassifications of noncontrolling interests	1	(1)
Adjustment to redemption value of redeemable noncontrolling interests	(12)
Cancellation of restricted stock for tax withholdings on vested shares	(1)	(2)
Share-based compensation	3	4
Equity, ending balance	(1,590)	(701)
Redeemable Noncontrolling Interests, ending balance	505
Redeemable Noncontrolling Interests [Member]
Redeemable Noncontrolling Interests, beginning balance	504	527
Comprehensive income (loss) attributable to redeemable noncontrolling interest	9	13
Contributions from noncontrolling interests	1
Distributions to redeemable noncontrolling interests	(19)	(17)
Purchase of subsidiary shares from noncontrolling interests	(1)	(1)
Other reclassifications of redeemable noncontrolling interests	(1)	1
Adjustment to redemption value of redeemable noncontrolling interests	12
Redeemable Noncontrolling Interests, ending balance	505	523
Common Stock [Member]
Equity, beginning balance	1	1
Equity, ending balance	1	1
Additional Paid-in Capital [Member]
Equity, beginning balance	2,017	2,014
Purchase of subsidiary shares from noncontrolling interests		(2)
Adjustment to redemption value of redeemable noncontrolling interests	(12)
Cancellation of restricted stock for tax withholdings on vested shares	(1)	(2)
Share-based compensation	3	4
Equity, ending balance	2,007	2,014
Accumulated Other Comprehensive Loss [Member]
Equity, beginning balance	(10)	(21)
Comprehensive income (loss)		17
Adoption of new accounting standards		(12)
Equity, ending balance	(10)	(16)
Accumulated Deficit [Member]
Equity, beginning balance	(3,543)	(2,761)
Comprehensive income (loss)	(118)	(25)
Adoption of new accounting standards		12
Equity, ending balance	(3,661)	(2,774)
Noncontrolling Interest [Member]
Equity, beginning balance	72	75
Comprehensive income (loss)	8	6
Distributions to noncontrolling interests	(8)	(6)
Other reclassifications of noncontrolling interests	1	(1)
Equity, ending balance	$ 73	$ 74