Pension and Other Benefits - Net Pension and Other Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.5	$ 1.0	$ 1.6	$ 3.2
Interest cost	8.7	8.6	26.0	25.8
Expected return on plan assets	(7.7)	(8.3)	(23.0)	(25.3)
Amortization of prior service cost	0.2	0.0	0.2	0.0
Amortization of actuarial losses	2.3	2.6	7.2	8.1
Settlement and curtailment losses	0.3	0.0	0.3	0.0
NET PERIODIC BENEFIT COST	4.3	3.9	12.3	11.8
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.0	0.1	0.1
Interest cost	0.2	0.2	0.8	0.7
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of prior service cost	(0.3)	(0.2)	(0.7)	(0.7)
Amortization of actuarial losses	0.1	0.0	0.1	0.1
Settlement and curtailment losses	0.0	0.0	0.0	0.0
NET PERIODIC BENEFIT COST	$ 0.1	$ 0.0	$ 0.3	$ 0.2