Pension and Other Benefits - Net Pension and Other Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.3	$ 0.2	$ 0.5	$ 0.5
Interest cost	6.0	7.2	12.0	14.4
Expected return on plan assets	(9.2)	(8.4)	(18.3)	(16.9)
Amortization of prior service cost	0.1	0.1	0.1	0.1
Amortization of actuarial losses	2.7	2.3	5.4	4.7
NET PERIODIC BENEFIT COST	(0.1)	1.4	(0.3)	2.8
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0	0.0
Interest cost	0.2	0.2	0.3	0.4
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of prior service cost	0.0	(0.1)	0.0	(0.2)
Amortization of actuarial losses	0.0	0.0	0.0	0.0
NET PERIODIC BENEFIT COST	$ 0.2	$ 0.1	$ 0.3	$ 0.2