CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Common stock par value (in dollars per share)	$ 0.01	$ 0.01
Common stock authorized (in shares)	199,300,000.0	199,300,000.0
Common stock issued (in shares)	105,200,000	105,200,000
Common stock outstanding (in shares)	89,900,000	88,000,000
Treasury stock at cost (in shares)	17,200,000	17,200,000