Pension and Other Benefits - Net Pension and Other Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.5	$ 1.1
Interest cost	8.7	8.6
Expected return on plan assets	(7.6)	(8.5)
Amortization of prior service cost	0.0	0.0
Amortization of actuarial losses	2.2	2.8
NET PERIODIC BENEFIT COST	3.8	4.0
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0
Interest cost	0.3	0.2
Expected return on plan assets	0.0	0.0
Amortization of prior service cost	(0.2)	(0.2)
Amortization of actuarial losses	0.0	0.0
NET PERIODIC BENEFIT COST	$ 0.1	$ 0.0