Share-Based Compensation Plans - Schedule of Compensation Costs by Value Driver Award Programs (Details) - Value Driver Award - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
2014 Value Driver Award Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	$ 0.0	$ 0.0	$ 1.3
2015 Value Driver Award Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	0.0	4.1	10.9
2016 Value Driver Award Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	7.0	16.3	0.0
2017 Value Driver Performance Share Unit Award Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	$ 10.3	$ 0.0	$ 0.0