CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) shares in Thousands, $ in Millions	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Treasury Stock	Noncontrolling Interests	Total
Balances at Dec. 31, 2013	$ 7	$ 4,572	$ (24)	$ (1,422)	$ (2,378)	$ 123	$ 878
Balances (in shares) at Dec. 31, 2013	96,860
Changes in Shareholders' Equity
Net income (loss)				12		31	43
Distributions paid to noncontrolling interests						(37)	(37)
Contributions from noncontrolling interests						7	7
Other comprehensive income (loss)			(158)				(158)
Purchases (sales) of businesses and noncontrolling interests		(22)				10	(12)
Stock-based compensation expense and issuance of common stock		64					64
Stock-based compensation expense and issuance of common stock (in shares)	1,522
Balances at Dec. 31, 2014	$ 7	4,614	(182)	(1,410)	(2,378)	134	785
Balances (in shares) at Dec. 31, 2014	98,382
Changes in Shareholders' Equity
Net income (loss)				(140)		52	(88)
Distributions paid to noncontrolling interests						(50)	(50)
Contributions from noncontrolling interests						3	3
Other comprehensive income (loss)			18				18
Purchases (sales) of businesses and noncontrolling interests		124				128	252
Repurchases of common stock					(40)		(40)
Repurchases of common stock (in shares)	(1,243)
Stock-based compensation expense and issuance of common stock		77			1		78
Stock-based compensation expense and issuance of common stock (in shares)	1,356
Balances at Dec. 31, 2015	$ 7	4,815	(164)	(1,550)	(2,417)	267	958
Balances (in shares) at Dec. 31, 2015	98,495
Changes in Shareholders' Equity
Net income (loss)				(192)		138	(54)
Distributions paid to noncontrolling interests						(111)	(111)
Other comprehensive income (loss)			(94)				(94)
Purchases (sales) of businesses and noncontrolling interests		(40)				146	106
Purchase accounting adjustments						225	225
Stock-based compensation expense and issuance of common stock		52					52
Stock-based compensation expense and issuance of common stock (in shares)	1,191
Balances at Dec. 31, 2016	$ 7	$ 4,827	$ (258)	$ (1,742)	$ (2,417)	$ 665	$ 1,082
Balances (in shares) at Dec. 31, 2016	99,686