Pension Benefits and Postretirement Benefits Other Than Pensions - Components of OPEB Benefits (Details) - Postretirement Benefits Other than Pensions - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	$ 0.0	$ 0.0	$ 0.1	$ 0.1
Interest Cost on Accumulated Postretirement Benefit Obligation	0.1	0.1	0.1	0.2
Amortization of Prior Service Credit	(0.4)	(0.4)	(0.7)	(0.7)
Amortization of Net Gain	(0.3)	(0.5)	(0.7)	(1.0)
Total Pension (Benefit) Expense	$ (0.6)	$ (0.8)	$ (1.2)	$ (1.4)