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, shares at Dec. 31, 2017		135.0
Balance, value at Dec. 31, 2017	$ 4,955	$ 2	$ 2,612	$ 7,138	$ (48)	$ (4,783)	$ 34
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	643			609			34
Other comprehensive income (loss), net of taxes	(8)				(8)
Dividends declared	(203)			(203)
Distributions to noncontrolling interest partners	(32)						(32)
Issuance of common stock under benefit plans	20		10			10
Stock-based compensation expense	53		49			4
Exercise of stock options, shares		2.0
Exercise of stock options, value	95		5			$ 90
Purchases of treasury stock, shares		(1.0)				(1.4)
Purchases of treasury stock, value	(150)					$ (150)
Contributions from noncontrolling interest partners	12						12
Reclassification of stranded tax effects resulting from enactment of the Tax Cut and Jobs Act	0			2	(2)
Balance, shares at Sep. 30, 2018		136.0
Balance, value at Sep. 30, 2018	5,365	$ 2	2,656	7,546	(58)	(4,829)	48
Balance, Value at Dec. 31, 2017	80
Redeemable Non-controlling Interest [Abstract]
Net income	6
Distributions to noncontrolling interest partners	(9)
Balance, Value at Sep. 30, 2018	77
Balance, shares at Jun. 30, 2018		136.0
Balance, value at Jun. 30, 2018	5,263	$ 2	2,633	7,401	(57)	(4,756)	40
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	224			213			11
Other comprehensive income (loss), net of taxes	(1)				(1)
Dividends declared	(68)			(68)
Distributions to noncontrolling interest partners	(11)						(11)
Issuance of common stock under benefit plans	7		4			3
Stock-based compensation expense	19		17			2
Exercise of stock options, shares		1.0
Exercise of stock options, value	24		2			22
Purchases of treasury stock, shares		(1.0)
Purchases of treasury stock, value	(100)					(100)
Contributions from noncontrolling interest partners	8						8
Balance, shares at Sep. 30, 2018		136.0
Balance, value at Sep. 30, 2018	5,365	$ 2	2,656	7,546	(58)	(4,829)	48
Balance, Value at Jun. 30, 2018	76
Redeemable Non-controlling Interest [Abstract]
Net income	3
Distributions to noncontrolling interest partners	(2)
Balance, Value at Sep. 30, 2018	77
Balance, shares at Dec. 31, 2018		135.0
Balance, value at Dec. 31, 2018	5,267	$ 2	2,667	7,602	(59)	(4,996)	51
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	637			605			32
Other comprehensive income (loss), net of taxes	4				4
Dividends declared	(215)			(215)
Distributions to noncontrolling interest partners	(34)						(34)
Issuance of common stock under benefit plans	19		7			12
Stock-based compensation expense	44		43			1
Exercise of stock options, shares		2.0
Exercise of stock options, value	98					$ 94
Purchases of treasury stock, shares		(2.0)				(1.6)
Purchases of treasury stock, value	(150)					$ (150)
Balance, shares at Sep. 30, 2019		135.0
Balance, value at Sep. 30, 2019	5,654	$ 2	2,705	7,992	(55)	(5,039)	49
Balance, Value at Dec. 31, 2018	77
Redeemable Non-controlling Interest [Abstract]
Net income	4
Distributions to noncontrolling interest partners	(5)
Balance, Value at Sep. 30, 2019	76
Balance, shares at Jun. 30, 2019		135.0
Balance, value at Jun. 30, 2019	5,509	$ 2	2,686	7,849	(58)	(5,020)	50
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	225			215			10
Other comprehensive income (loss), net of taxes	3				3
Dividends declared	(72)			(72)
Distributions to noncontrolling interest partners	(11)						(11)
Issuance of common stock under benefit plans	6		3			3
Stock-based compensation expense	12		12
Exercise of stock options, shares		1.0
Exercise of stock options, value	32		4			28
Purchases of treasury stock, shares		(1.0)
Purchases of treasury stock, value	(50)					(50)
Balance, shares at Sep. 30, 2019		135.0
Balance, value at Sep. 30, 2019	5,654	$ 2	$ 2,705	$ 7,992	$ (55)	$ (5,039)	$ 49
Balance, Value at Jun. 30, 2019	76
Redeemable Non-controlling Interest [Abstract]
Net income	1
Distributions to noncontrolling interest partners	(1)
Balance, Value at Sep. 30, 2019	$ 76