CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (PARENTHETICAL) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts		$ 25	$ 25
Accumulated depreciation		$ 1,519	$ 1,471
Preferred stock, par value (in dollars per share)		$ 0.01	$ 0.01
Preferred stock, shares authorized		1,000,000,000	1,000,000,000
Preferred stock, shares issued		0	0
Common stock, par value (in dollars per share)		$ 0.01	$ 0.01
Common stock, shares authorized		6,000,000,000	6,000,000,000
Common stock issued, shares	[1]	501,891,243	501,891,243
Common stock, shares outstanding		484,724,245	486,130,461
Treasury stock, shares	[1]	17,166,998	15,760,782

[1] Shares may not add due to rounding.