Supplemental Information - Other Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred compensation arrangements (Note 5)	$ 2.0	$ 0.7
Pension & OPEB liabilities (Note 13)	7.0	5.9
Unrecognized tax benefits (Note 17)	0.5	1.0
Other	3.7	2.6
Other liabilities	$ 13.2	$ 10.2