Pension Benefits - Changes in Fair Value of Pension Plans Level 3 (Details) - Pension Plans, Defined Benefit - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plans’ Assets at Beginning of Year	$ 664.6	$ 525.3
Fair Value of Plan Assets at End of Year	405.4	664.6
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plans’ Assets at Beginning of Year	0.0	0.3
Purchases, Sales and Settlements, Net	0.0	(0.3)
Fair Value of Plan Assets at End of Year	$ 0.0	$ 0.0