Pension and Postretirement Plans - Schedule of Pension and Postretirement Costs (Benefits) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
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	5.9	5.9	17.9	14.2
Expected return on plan assets	(7.7)	(8.7)	(23.0)	(21.1)
Amortization of:
Prior service benefit	0.0	0.0	0.0	0.0
Actuarial loss	3.5	4.2	10.3	12.7
Total amortization	3.5	4.2	10.3	12.7
Pension / postretirement costs	1.7	1.4	5.2	5.8
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0.2	0.3	0.5	0.4
Other components of pension and postretirement benefit plans expense:
Interest cost on projected benefit obligation	1.3	1.3	3.8	2.9
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of:
Prior service benefit	(0.6)	(0.7)	(1.9)	(2.3)
Actuarial loss	0.4	1.0	1.3	3.1
Total amortization	(0.2)	0.3	(0.6)	0.8
Pension / postretirement costs	$ 1.3	$ 1.9	$ 3.7	$ 4.1