Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for Doubtful Accounts	$ 7	$ 6
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	100,000,000	100,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	1,500,000,000	1,500,000,000
Common stock, shares, issued (in shares)	604,000,000	600,000,000
Common stock, shares, outstanding (in shares)	569,000,000	583,000,000
Treasury stock, shares (in shares)	35,000,000	17,000,000