CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts	$ 1	$ 1
Shareholders' Equity:
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000	200,000,000
Common stock, shares issued	129,903,498	129,189,634
Common stock, shares, outstanding	123,060,638	123,328,051
Treasury stock, shares	6,842,860	5,861,583