Pension and Postretirement Plans - Schedule of Pension and Postretirement Costs (Benefits) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 0.0	$ 0.0
Other components of pension and postretirement benefit plans expense:
Interest cost on projected benefit obligation	4.8	6.0
Expected return on plan assets	(7.3)	(7.8)
Amortization of:
Prior service benefit	0.0	0.0
Actuarial loss	4.5	3.4
Total amortization	4.5	3.4
Pension / postretirement costs	2.0	1.6
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0.1	0.2
Other components of pension and postretirement benefit plans expense:
Interest cost on projected benefit obligation	0.9	1.2
Expected return on plan assets	0.0	0.0
Amortization of:
Prior service benefit	(0.6)	(0.6)
Actuarial loss	0.2	0.4
Total amortization	(0.4)	(0.2)
Pension / postretirement costs	$ 0.6	$ 1.2