Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 8	$ 7
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, authorized (in shares)	100,000,000	100,000,000
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	1,500,000,000	1,500,000,000
Common stock, issued (in shares)	607,000,000	604,000,000
Common stock, outstanding (in shares)	558,000,000	569,000,000
Treasury stock (in shares)	49,000,000	35,000,000