Consolidated Balance Sheet (Parenthetical) (Unaudited) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Trade, allowance for doubtful accounts	$ 6	$ 5
Deferred debt issuance costs	$ 23	$ 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, outstanding	143,813,145	150,068,040
Treasury stock, shares	6,810,678	23,963