Pension Benefits - Changes in Fair Value of Pension Plans Level 3 (Details) - Pension Plans, Defined Benefit - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plans’ Assets at Beginning of Year	$ 525.3	$ 579.8
Fair Value of Plan Assets at End of Year	664.6	525.3
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	0.3	0.3
Purchases, Sales and Settlements, Net	(0.3)	0.0
Fair Value of Plan Assets at End of Year	$ 0.0	$ 0.3