Benefit Plans - Amounts Recognized in Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Current liabilities	$ (2.3)	$ (2.2)
Noncurrent liabilities	(57.5)	(52.5)
Pension benefits
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Noncurrent assets	12.9	4.3
Current liabilities	(1.6)	(1.5)
Noncurrent liabilities	(52.1)	(46.6)
Total liabilities	(40.8)	(43.8)
Other retirement benefits
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Noncurrent assets	0.0	0.0
Current liabilities	(0.7)	(0.7)
Noncurrent liabilities	(5.4)	(5.9)
Total liabilities	$ (6.1)	$ (6.6)