Pension Benefits - Components of Comprehensive Pension Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Settlement Expense	$ 64.1	$ 0.0	$ 0.0
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service Cost Earned During the Year	0.0	0.0	0.0
Interest Cost on Projected Benefit Obligation	16.5	22.3	20.3
Expected Return on Plan Assets	(27.6)	(30.6)	(28.9)
Amortization of Actuarial Loss	5.6	2.9	4.3
Pension Expense (Income) Recognized in Consolidated Statements of Income	58.6	(5.4)	(4.3)
Unrecognized Pension Gain (Loss) Arising During the Year	(7.8)	4.2	11.5
Amortization of Accumulated Unrecognized Pension Loss	(69.8)	(2.9)	(4.3)
Comprehensive Pension Expense (Income)	$ (19.0)	$ (4.1)	$ 2.9