Consolidated Balance Sheet (Parenthetical) (Unaudited) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Trade, allowance for doubtful accounts	$ 9	$ 8
Deferred debt issuance costs	$ 20	$ 22
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	450,000,000	450,000,000
Common stock, outstanding	144,544,641	144,984,050
Treasury stock, shares	8,255,763	7,001,017