Stockholders' Deficit (Schedule of Stockholders' Deficit) (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Equity, beginning balance	$ (1,759)	$ (1,590)	$ (1,463)	$ (803)	$ (701)	$ (692)
Redeemable Noncontrolling Interests, beginning balance			504
Comprehensive income (loss)	(9)	(157)	(110)	(317)	(93)	(2)
Contributions from redeemable noncontrolling interests	7			1	1
Distributions to noncontrolling interests	(7)	(8)	(8)	(6)	(9)	(6)
Purchase of subsidiary shares from noncontrolling interests	3	(1)		(4)	(2)	(2)
Other reclassifications of noncontrolling interests	1		1	(1)	1	(1)
Adjustment to redemption value of redeemable noncontrolling interests	(3)	(6)	(12)	(1)	(5)
Cancellation of restricted stock for tax withholdings on vested shares			(1)	(2)	2	(2)
Share-based compensation	2	3	3	3	3	4
Equity, ending balance	(1,765)	(1,759)	(1,590)	(1,130)	(803)	(701)
Redeemable Noncontrolling Interests, ending balance	498
Redeemable Noncontrolling Interests [Member]
Redeemable Noncontrolling Interests, beginning balance	503	505	504	514	523	527
Comprehensive income (loss) attributable to redeemable noncontrolling interest	11	14	9	11	8	13
Contributions from redeemable noncontrolling interests	1	1	1
Distributions to redeemable noncontrolling interests	(14)	(22)	(19)	(16)	(20)	(17)
Purchase of subsidiary shares from noncontrolling interests	(6)		(1)	(22)	(1)	(1)
Other reclassifications of redeemable noncontrolling interests		(1)	(1)	1	(1)	1
Redeemable noncontrolling interests in acquired entity				6
Adjustment to redemption value of redeemable noncontrolling interests	3	6	12	1	5
Redeemable Noncontrolling Interests, ending balance	498	503	505	495	514	523
Common Stock [Member]
Equity, beginning balance	1	1	1	1	1	1
Equity, ending balance	1	1	1	1	1	1
Additional Paid-in Capital [Member]
Equity, beginning balance	2,002	2,007	2,017	2,013	2,014	2,014
Purchase of subsidiary shares from noncontrolling interests	2	(1)		(2)	(1)	(2)
Other reclassifications of noncontrolling interests	1	(1)
Adjustment to redemption value of redeemable noncontrolling interests	(3)	(6)	(12)	(1)	(5)
Cancellation of restricted stock for tax withholdings on vested shares			(1)	(2)	2	(2)
Share-based compensation	2	3	3	3	3	4
Equity, ending balance	2,004	2,002	2,007	2,011	2,013	2,014
Accumulated Other Comprehensive Loss [Member]
Equity, beginning balance	(8)	(10)	(10)	(9)	(16)	(21)
Comprehensive income (loss)		2		1	7	17
Adoption of new accounting standards						(12)
Equity, ending balance	(8)	(8)	(10)	(8)	(9)	(16)
Accumulated Deficit [Member]
Equity, beginning balance	(3,828)	(3,661)	(3,543)	(2,884)	(2,774)	(2,761)
Comprehensive income (loss)	(17)	(167)	(118)	(325)	(110)	(25)
Adoption of new accounting standards						12
Equity, ending balance	(3,845)	(3,828)	(3,661)	(3,209)	(2,884)	(2,774)
Noncontrolling Interest [Member]
Equity, beginning balance	74	73	72	76	74	75
Comprehensive income (loss)	8	8	8	7	10	6
Contributions from redeemable noncontrolling interests	7			1	1
Distributions to noncontrolling interests	(7)	(8)	(8)	(6)	(9)	(6)
Purchase of subsidiary shares from noncontrolling interests	1			(2)	(1)
Other reclassifications of noncontrolling interests		1	1	(1)	1	(1)
Equity, ending balance	$ 83	$ 74	$ 73	$ 75	$ 76	$ 74