Summary of Significant Accounting Policies - Changes in the Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pre-tax	$ 5.7	$ (2.9)
Tax	5.0	4.8
Other comprehensive income (loss)	10.7	1.9	$ (30.2)
Including cumulative effect adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pre-tax			(31.3)
Tax			(3.8)
Other comprehensive income (loss)			(35.1)
Pension and OPEB liability adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pre-tax	5.0	2.5
Tax	(1.2)	1.4
Other comprehensive income (loss)	3.8	3.9
Pension and OPEB liability adjustments | Including cumulative effect adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pre-tax			(0.9)
Tax			(2.4)
Other comprehensive income (loss)			(3.3)
Derivative instrument adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pre-tax	(10.8)	(2.9)
Tax	1.2	0.0
Other comprehensive income (loss)	(9.6)	(2.9)
Derivative instrument adjustments | Including cumulative effect adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pre-tax			(2.4)
Tax			1.4
Other comprehensive income (loss)			(1.0)
Unrealized foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pre-tax	11.5	(2.5)
Tax	5.0	3.4
Other comprehensive income (loss)	$ 16.5	$ 0.9
Unrealized foreign currency translation adjustments | Including cumulative effect adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pre-tax			(28.0)
Tax			(2.8)
Other comprehensive income (loss)			$ (30.8)