Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Preferred stock, authorized (in shares)	40,000,000	40,000,000
Preferred stock, issued (in shares)	0	0
common shares, par value (in usd per share)	$ 0.01	$ 0.01
common shares, authorized (in shares)	400,000,000	400,000,000
common shares, issued (in shares)	122,200,000	122,200,000
Treasury stock, shares (in shares)	36,900,000	32,900,000