Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Trade, allowance for doubtful accounts	$ 5	$ 6
Debt issuance costs	$ 21	$ 25
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	150,068,040	166,070,057
Treasury stock, shares	23,963	1,588,990