Pension and Postretirement Benefit Costs - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Mark-To-Market Adjustment on Actuarially Determined Liabilities	$ 0.0	$ 13.0	$ 0.0	$ 13.0
Defined Benefit Plan, Benefit Obligation	$ 160.0		$ 160.0
Defined benefit pension plans
Defined Benefit Plan Disclosure [Line Items]
Funding threshold	80.00%		80.00%