Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Trade, allowance for doubtful accounts	$ 8	$ 6
Debt issuance costs	$ 22	$ 21
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares outstanding	0	0
Common stock, shares authorized	450,000,000	450,000,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares outstanding	144,984,050	143,938,280
Treasury stock, shares	7,001,017	6,812,784