Consolidated Statements of Change in Equity, Accumulated Other Comprehensive Loss and Redeemable Non-Controlling Interest - USD ($) $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Non- Controlling Interest in Consolidated Subsidiaries	Redeemable Non-Controlling Interest
Beginning Balance (in shares) at Dec. 31, 2016		596,000,000	1,000,000
Beginning Balance at Dec. 31, 2016	$ 15,775	$ 6	$ (40)	$ 11,306	$ 4,810	$ (344)	$ 37	$ 36
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income	121					121
Exercise of common stock options	17			17
Repurchases of common stock (in shares)			(15,000,000)
Repurchases of common stock	(949)		$ (949)
Payments relating to treasury shares (in shares)			(1,000,000)
Payments relating to treasury shares	(88)		$ (88)
Stock-based compensation	152			152
Issuance of restricted stock (in shares)		4,000,000
Issuance of restricted stock	0		$ 1	(1)
Acquisition of non-controlling interest	(92)			(82)			(10)
Distributions of profits	(26)						(26)
Dividends paid to stockholders	(476)				(476)
Acquisition of redeemable non-controlling interest	(2)				(2)			(37)
Net income attributable to non-controlling interest	(1)				(28)		27	1
Net income	$ 2,554				2,554
Ending Balance (in shares) at Dec. 31, 2017	600,000,000	600,000,000	17,000,000
Ending Balance at Dec. 31, 2017	$ 16,985	$ 6	$ (1,076)	11,392	6,858	(223)	28
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income	(42)					(42)
Exercise of common stock options	$ 12			12
Repurchases of common stock (in shares)	(10,403,246)		(10,000,000)
Repurchases of common stock	$ (759)		$ (759)
Payments relating to treasury shares (in shares)			(2,000,000)
Payments relating to treasury shares	(76)		$ (76)
Stock-based compensation	73			73
Issuance of restricted stock (in shares)		3,000,000
Issuance of restricted stock	0
Distributions of profits	(10)						(10)
Dividends paid to stockholders	(279)				(279)
Net income attributable to non-controlling interest	0				(17)		17
Net income	$ 936				936
Ending Balance (in shares) at Jun. 30, 2018	603,000,000	603,000,000	29,000,000
Ending Balance at Jun. 30, 2018	$ 16,840	$ 6	$ (1,911)	$ 11,477	$ 7,498	$ (265)	$ 35	$ 0