Pension and Other Post-Retirement Benefits - Components of Net Periodic Cost (Benefit) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Pension [Member]
Components of pension and other post retirement benefit costs
Service cost	$ 2.0	$ 1.7
Interest cost	3.1	3.8
Expected return on plan assets	(5.1)	(5.5)
Defined Benefit Plan, Amortization of Gain (Loss)	(3.1)	(1.9)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	3.1	1.9
Retiree Health and Life [Member]
Components of pension and other post retirement benefit costs
Service cost	0.0	0.0
Interest cost	0.1	0.2
Expected return on plan assets	0.0	0.0
Defined Benefit Plan, Amortization of Gain (Loss)	0.0	0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 0.1	$ 0.2