CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accounts receivable, net of allowance for doubtful accounts of $104 at March 31, 2019 and $93 at December 31, 2018	$ 104	$ 93
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Common stock, shares issued (in shares)	113,516,258	112,907,209
Common stock, shares outstanding (in shares)	78,812,644	79,872,956
Treasury stock, shares (in shares)	34,703,614	33,034,253