Pension Plans and Other Postretirement Benefits - Pension and Postretirement Plan Contributions (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Retirement Benefits [Abstract]
Employer contributions	$ 2.7	$ 2.1	$ 7.9	$ 8.6
Payment for other postretirement benefits	$ 0.9	$ 0.8	$ 2.5	$ 2.1