Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Trade, allowance for doubtful accounts	$ 6	$ 5
Debt issuance costs	$ 21	$ 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	143,938,280	150,068,040
Treasury stock, shares	6,812,784	23,963