Benefit Plans - Changes in Projected Benefit Obligation, Fair Value of Plan Assets and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in plan assets:
Balance	$ 244.1
Balance	258.1	$ 244.1
Pension benefits
Change in benefit obligation:
Balance	(287.9)	(267.0)
Service cost	(1.5)	(1.4)	$ (10.8)
Interest cost	(7.1)	(9.2)	(9.4)
Participants’ contributions	(0.3)	(0.3)
Actuarial (loss) gain	(22.1)	(30.8)
Benefits paid	6.2	6.8
Curtailment gain	0.1	0.0
Settlement loss	18.6	15.0
Foreign currency translation	(4.9)	(1.0)
Balance	(298.9)	(287.9)	(267.0)
Change in plan assets:
Balance	244.1	214.5
Actual return on plan assets	31.8	41.3
Employer contribution	4.8	8.0
Participants’ contributions	0.3	0.3
Benefits paid	(6.0)	(6.3)
Settlement loss	(18.6)	(15.0)
Foreign currency translation	1.7	1.3
Balance	258.1	244.1	214.5
Funded status at end of year	(40.8)	(43.8)
Other retirement benefits
Change in benefit obligation:
Balance	(6.6)	(6.0)
Service cost	0.0	0.0	0.0
Interest cost	(0.2)	(0.2)	(0.2)
Participants’ contributions	(0.1)	(0.7)
Actuarial (loss) gain	0.5	(0.2)
Benefits paid	0.3	0.5
Curtailment gain	0.0	0.0
Settlement loss	0.0	0.0
Foreign currency translation	0.0	0.0
Balance	(6.1)	(6.6)	(6.0)
Change in plan assets:
Balance	0.0	0.0
Actual return on plan assets	0.0	0.0
Employer contribution	0.2	(0.2)
Participants’ contributions	0.1	0.7
Benefits paid	(0.3)	(0.5)
Settlement loss	0.0	0.0
Foreign currency translation	0.0	0.0
Balance	0.0	0.0	$ 0.0
Funded status at end of year	$ (6.1)	$ (6.6)