Postretirement Benefits Other than Pensions - Discount Rate to Determine the Net Postretirement Benefit Expense (Details) - Other Postretirement Benefit Plan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (as a percent)	2.70%	3.83%	3.15%
Expected contribution to plan in 2019	$ 0.2