Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension benefits
Net periodic benefit cost:
Service cost	$ 1.5	$ 1.4	$ 10.8
Interest cost	7.1	9.2	9.4
Expected return on plan assets	(11.7)	(12.0)	(15.7)
Amortization of prior service credit	0.1	0.1	(1.3)
Amortization of actuarial loss (gain)	2.0	2.1	3.8
Settlement loss	3.7	3.5	0.0
Net periodic benefit cost	2.7	4.3	7.0
Other changes in plan assets and benefit obligations recognized in OCI, pre-tax:
Net loss (gain) arising during period	1.8	1.5	3.5
Prior service credit arising during period	0.0	0.0	0.3
Amortization of prior service credit	(0.1)	(0.1)	1.3
Amortization of actuarial (loss) gain	(2.0)	(2.1)	(3.8)
Settlement loss	(3.7)	(3.5)	0.0
Foreign currency translation	1.8	0.6	(1.2)
Total recognized in OCI	(2.2)	(3.6)	0.1
Total recognized in net periodic benefit cost and OCI	0.5	0.7	7.1
Pension benefits | United States
Net periodic benefit cost:
Net periodic benefit cost	1.2	2.4	4.8
Pension benefits | International plans
Net periodic benefit cost:
Net periodic benefit cost	1.5	1.9	2.2
Other retirement benefits
Net periodic benefit cost:
Service cost	0.0	0.0	0.0
Interest cost	0.2	0.2	0.2
Expected return on plan assets	0.0	0.0	0.0
Amortization of prior service credit	(0.7)	(0.7)	(0.7)
Amortization of actuarial loss (gain)	(1.9)	(2.3)	(2.4)
Settlement loss	0.0	0.0	0.0
Net periodic benefit cost	(2.4)	(2.8)	(2.9)
Other changes in plan assets and benefit obligations recognized in OCI, pre-tax:
Net loss (gain) arising during period	(0.4)	0.1	(1.4)
Prior service credit arising during period	0.0	0.0	0.0
Amortization of prior service credit	0.7	0.7	0.7
Amortization of actuarial (loss) gain	1.9	2.3	2.4
Settlement loss	0.0	0.0	0.0
Foreign currency translation	0.0	0.0	0.0
Total recognized in OCI	2.2	3.1	1.7
Total recognized in net periodic benefit cost and OCI	(0.2)	0.3	(1.2)
Other retirement benefits | United States
Net periodic benefit cost:
Net periodic benefit cost	(2.4)	(2.8)	(2.9)
Other retirement benefits | International plans
Net periodic benefit cost:
Net periodic benefit cost	$ 0.0	$ 0.0	$ 0.0