CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock, at Cost	Non-controlling Interests
Balance, value at Dec. 31, 2017	$ 4,955	$ 2	$ 2,612	$ 7,138	$ (48)	$ (4,783)	$ 34
Balance, shares at Dec. 31, 2017		135.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	188			177			11
Other comprehensive income, net of taxes	7				7
Dividends declared	(66)			(66)
Distributions to noncontrolling interest partners	(11)						(11)
Issuance of common stock under benefit plans	8		4			4
Stock-based compensation expense	19		18			1
Exercise of stock options, value	34		2			32
Exercise of stock options, shares		1.0
Shares to cover employee payroll tax withholdings on stock issued under stock-based compensation plans, value	(20)		(20)
Purchases of treasury stock, value	(50)					$ (50)
Purchases of treasury stock, shares						(0.5)
Contributions from noncontrolling interest partners	2						2
Balance, value at Mar. 31, 2018	5,066	$ 2	2,616	7,249	(41)	$ (4,796)	36
Balance, shares at Mar. 31, 2018		136.0
Balance, Value at Dec. 31, 2017	80
Redeemable Non-controlling Interest [Abstract]
Net income	1
Distributions to noncontrolling interest partners	(4)
Balance, Value at Mar. 31, 2018	77
Balance, value at Dec. 31, 2018	5,267	$ 2	2,667	7,602	(59)	(4,996)	51
Balance, shares at Dec. 31, 2018		135.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	174			164			10
Other comprehensive income, net of taxes	4				4
Dividends declared	(72)			(72)
Distributions to noncontrolling interest partners	(10)						(10)
Issuance of common stock under benefit plans	6		2			4
Stock-based compensation expense	17		16			1
Exercise of stock options, value	20		1			19
Exercise of stock options, shares
Shares to cover employee payroll tax withholdings on stock issued under stock-based compensation plans, value	(15)		(15)
Purchases of treasury stock, value	(50)					$ (50)
Purchases of treasury stock, shares		(1.0)				(0.6)
Balance, value at Mar. 31, 2019	5,341	$ 2	$ 2,671	$ 7,694	$ (55)	$ (5,022)	$ 51
Balance, shares at Mar. 31, 2019		134.0
Balance, Value at Dec. 31, 2018	77
Redeemable Non-controlling Interest [Abstract]
Net income	2
Distributions to noncontrolling interest partners	(2)
Balance, Value at Mar. 31, 2019	$ 77