Pension and Postretirement Plans - Schedule of Pension and Postretirement Costs (Benefits) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 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	4.6	5.9	14.2	17.9
Expected return on plan assets	(7.1)	(7.7)	(21.6)	(23.0)
Amortization of:
Prior service benefit	0.0	0.0	0.0	0.0
Actuarial loss	4.5	3.5	13.5	10.3
Pension settlement charges			1.1	0.0
Pension / postretirement costs	2.0	1.7	7.2	5.2
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0.1	0.2	0.3	0.5
Other components of pension and postretirement benefit plans expense:
Interest cost on projected benefit obligation	0.9	1.3	2.8	3.8
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of:
Prior service benefit	(0.6)	(0.6)	(1.9)	(1.9)
Actuarial loss	0.3	0.4	0.9	1.3
Pension settlement charges			0.0	0.0
Pension / postretirement costs	$ 0.7	$ 1.3	$ 2.1	$ 3.7