Pension Benefits - Components of Comprehensive Pension Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Unrecognized Pension Gain (Loss) Arising During the Year	$ 4.8	$ 8.0	$ (3.9)
Amortization of Accumulated Unrecognized Pension Loss	3.0	(1.1)	0.6
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	22.3	20.3	20.6
Expected Return on Plan Assets	(30.6)	(28.9)	(30.9)
Amortization of Actuarial Loss	2.9	4.3	2.6
Pension Income Recognized in Consolidated Statements of Income	(5.4)	(4.3)	(7.7)
Unrecognized Pension Gain (Loss) Arising During the Year	4.2	11.5	(4.9)
Amortization of Accumulated Unrecognized Pension Loss	(2.9)	(4.3)	(2.6)
Comprehensive Pension Expense (Income)	$ (4.1)	$ 2.9	$ (15.2)