Pension Benefits and Postretirement Benefits Other Than Pensions - Components of OPEB Benefits (Details) - Postretirement Benefits Other than Pensions - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	$ 0.1	$ 0.1
Interest Cost on Accumulated Postretirement Benefit Obligation	0.1	0.1
Amortization of Prior Service Credit	(0.3)	(0.3)
Amortization of Net Gain	(0.5)	(0.5)
Total Pension Benefit Recognized	$ (0.6)	$ (0.6)