Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Receivables, allowance for doubtful accounts	$ 36	$ 38
Preferred stock,par value	$ 0.01	$ 0.01
Preferred stock,shares authorized	10,000,000	10,000,000
Preferred stock,shares issued	0	0
Preferred stock,shares outstanding	0	0
Common stock,par value	$ 0.01	$ 0.01
Common stock,shares authorized	250,000,000	250,000,000
Common stock,shares issued	137,000,000	137,000,000
Treasury stock,shares	56,000,000	51,000,000