Pension and Postretirement Plans - Schedule of Pension and Postretirement Costs (Benefits) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	6.0	4.1	12.0	8.3
Expected return on plan assets	(7.5)	(6.2)	(15.3)	(12.4)
Amortization of:
Prior service benefit	0.0	0.0	0.0	0.0
Actuarial loss	3.4	4.2	6.8	8.5
Total amortization	3.4	4.2	6.8	8.5
Pension / postretirement costs	1.9	2.1	3.5	4.4
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0.1	0.0	0.3	0.1
Other components of pension and postretirement benefit plans expense:
Interest cost on projected benefit obligation	1.3	0.8	2.5	1.6
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of:
Prior service benefit	(0.7)	(0.8)	(1.3)	(1.6)
Actuarial loss	0.5	1.1	0.9	2.1
Total amortization	(0.2)	0.3	(0.4)	0.5
Pension / postretirement costs	$ 1.2	$ 1.1	$ 2.4	$ 2.2