Benefit Plans - Pension and Other Postretirement Benefit Liabilities in Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Total Pension and Other Postretirement Benefit Liabilities Included in Balance Sheets [Abstract]
Other assets	$ 2.3	$ 2.3
Accrued liabilities	(17.9)	(2.2)
Pension and other postretirement benefits	$ (269.1)	$ (99.7)