Stockholders' Deficit - Schedule of Stockholders' Deficit (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019
Equity, beginning balance	$ (2,052)	$ (2,136)	$ (2,141)	$ (1,759)	$ (1,590)	$ (1,463)
Redeemable Noncontrolling Interests, beginning balance			502
Comprehensive income (loss)	104	87	28	(9)	(157)	(110)
Contributions from noncontrolling interests				7
Distributions to noncontrolling interests	(7)	(10)	(8)	(7)	(8)	(8)
Purchase of subsidiary shares from noncontrolling interests		1	(1)	3	(1)
Other reclassifications of noncontrolling interests			(8)	1		1
Adjustment to redemption value of redeemable noncontrolling interests	(6)	3	(7)	(3)	(6)	(12)
Cancellation of restricted stock for tax withholdings on vested shares			(1)			(1)
Share-based compensation	3	3	2	2	3	3
Equity, ending balance	(1,957)	(2,052)	(2,136)	(1,765)	(1,759)	(1,590)
Redeemable Noncontrolling Interests, ending balance	481
Redeemable Noncontrolling Interests (Non- Equity)
Redeemable Noncontrolling Interests, beginning balance	489	502	502	503	505	504
Comprehensive income (loss)	23
Comprehensive income (loss) attributable to redeemable noncontrolling interest		7	8	11	14	9
Contributions from noncontrolling interests				1	1	1
Distributions to redeemable noncontrolling interests	(20)	(17)	(22)	(14)	(22)	(19)
Purchase of subsidiary shares from noncontrolling interests	(2)	(1)	(1)	(6)		(1)
Disposition of less-than-wholly owned hospital	(15)
Other reclassifications of redeemable noncontrolling interests		1	8		(1)	(1)
Adjustment to redemption value of redeemable noncontrolling interests	6	(3)	7	3	6	12
Redeemable Noncontrolling Interests, ending balance	481	489	502	498	503	505
Common Stock
Equity, beginning balance	1	1	1	1	1	1
Equity, ending balance	1	1	1	1	1	1
Additional Paid-in Capital
Equity, beginning balance	2,008	2,001	2,008	2,002	2,007	2,017
Purchase of subsidiary shares from noncontrolling interests		1	(1)	2	(1)
Other reclassifications of noncontrolling interests				1	(1)
Adjustment to redemption value of redeemable noncontrolling interests	(6)	3	(7)	(3)	(6)	(12)
Cancellation of restricted stock for tax withholdings on vested shares			(1)			(1)
Share-based compensation	3	3	2	2	3	3
Equity, ending balance	2,005	2,008	2,001	2,004	2,002	2,007
Accumulated Other Comprehensive Income (Loss)
Equity, beginning balance	(5)	(7)	(9)	(8)	(10)	(10)
Comprehensive income (loss)		2	2		2
Equity, ending balance	(5)	(5)	(7)	(8)	(8)	(10)
Accumulated Deficit
Equity, beginning balance	(4,131)	(4,200)	(4,218)	(3,828)	(3,661)	(3,543)
Comprehensive income (loss)	112	69	18	(17)	(167)	(118)
Equity, ending balance	(4,018)	(4,131)	(4,200)	(3,845)	(3,828)	(3,661)
Noncontrolling Interest
Equity, beginning balance	75	69	77	74	73	72
Comprehensive income (loss)	(8)	16	8	8	8	8
Contributions from noncontrolling interests				7
Distributions to noncontrolling interests	(7)	(10)	(8)	(7)	(8)	(8)
Purchase of subsidiary shares from noncontrolling interests				1
Other reclassifications of noncontrolling interests			(8)		1	1
Equity, ending balance	$ 60	$ 75	$ 69	$ 83	$ 74	$ 73