Pension and Postretirement Plans - Schedule of Pension and Postretirement Costs (Benefits) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Other components of pension and postretirement benefit plans expense:
Interest cost on projected benefit obligation	4.8	6.0	9.6	12.0
Expected return on plan assets	(7.2)	(7.5)	(14.5)	(15.3)
Amortization of:
Prior service benefit	0.0	0.0	0.0	0.0
Actuarial loss	4.5	3.4	9.0	6.8
Pension settlement charges	1.1	0.0	1.1	0.0
Pension / postretirement costs	3.2	1.9	5.2	3.5
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0.1	0.1	0.2	0.3
Other components of pension and postretirement benefit plans expense:
Interest cost on projected benefit obligation	1.0	1.3	1.9	2.5
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of:
Prior service benefit	(0.7)	(0.7)	(1.3)	(1.3)
Actuarial loss	0.4	0.5	0.6	0.9
Pension settlement charges	0.0	0.0	0.0	0.0
Pension / postretirement costs	$ 0.8	$ 1.2	$ 1.4	$ 2.4