Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 6.2	$ 5.9
Preferred shares, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred shares, authorized (in shares)	100.0	100.0
Preferred shares, issued (in shares)	0.0	0.0
Preferred shares, outstanding (in shares)	0.0	0.0
Common shares, par value (in dollars per share)	$ 0.01	$ 0.01
Common shares, authorized (in shares)	1,000.0	1,000.0
Common shares, issued (in shares)	153.1	160.3
Common shares, outstanding (in shares)	153.0	160.3
Treasury shares, par value (in dollars per share)	$ 0.01
Treasury stock, shares held (in shares)	0.1	0.0