Benefit Plans - Pension and Other Post-retirement Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Vesting period	3 years
Plan assets	$ 33.7	$ 31.0
Company contributions		11.1
Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Periodic Benefit (Cost) Credit		(11.8)
Pension plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Lump-sum payments	0.0	(1.5)
Benefit obligation	120.8	112.1	$ 277.9
Plan assets	33.7	31.0	180.7
Company contributions	$ 7.1	$ 18.0
Pension plans | Salaried Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Lump-sum payments			$ 171.9
Restricted Stock And Restricted Stock Units (RSUs) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Vesting period	3 years