Retirement Plans and Other Postretirement Benefits - Defined Benefit Plan and Supplemental Retirement Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan
Change in benefit obligation:
Projected benefit obligation at beginning of year	$ 24.3	$ 24.8	$ 25.1
Service cost	0.6	0.7	0.7
Interest cost	0.5	0.7	1.0
Actuarial loss (gain)	(0.6)	1.0	0.0
Benefits paid	(2.6)	(1.5)	(2.0)
Settlements	0.0	(1.4)	0.0
Projected benefit obligation at end of year	22.2	24.3	24.8
Change in plan assets:
Fair value of plan assets at beginning of year	22.0	23.2	22.1
Actual return on plan assets	1.0	2.3	3.5
Employer contributions	0.0	0.0	0.0
Benefits paid	(2.6)	(1.5)	(2.0)
Expenses paid	(0.6)	(0.6)	(0.4)
Settlements	0.0	(1.4)	0.0
Fair value of plan assets at end of year	19.8	22.0	23.2
Funded status	(2.4)	(2.3)	(1.6)
Prepaid (accrued) benefit expense	4.9	5.5	6.7
Total amount recognized in Consolidated Balance Sheets, all in Other liabilities	(2.4)	(2.3)	(1.7)
Amounts recognized in accumulated other comprehensive income (loss) (AOCI):
Prior service cost	0.0	0.0	0.0
Net actuarial loss	(7.3)	(7.8)	(8.3)
Total amount recognized in AOCI	(7.3)	(7.8)	(8.3)
Information for pension plans with an accumulated benefit obligation greater than plan assets:
Projected benefit obligation	22.2	24.3	24.8
Accumulated benefit obligation	22.2	24.3	24.8
Fair value of plan assets	19.8	22.0	23.2
Supplemental Defined Benefit Plans
Change in benefit obligation:
Projected benefit obligation at beginning of year	15.7	15.2	15.4
Service cost	0.0	0.0	0.0
Interest cost	0.3	0.5	0.6
Actuarial loss (gain)	(0.2)	1.3	0.5
Benefits paid	(1.3)	(1.3)	(1.3)
Settlements	0.0	0.0	0.0
Projected benefit obligation at end of year	14.5	15.7	15.2
Change in plan assets:
Fair value of plan assets at beginning of year	0.0	0.0	0.0
Actual return on plan assets	0.0	0.0	0.0
Employer contributions	1.3	1.3	1.3
Benefits paid	(1.3)	(1.3)	(1.3)
Expenses paid	0.0	0.0	0.0
Settlements	0.0	0.0	0.0
Fair value of plan assets at end of year	0.0	0.0	0.0
Funded status	(14.5)	(15.7)	(15.2)
Prepaid (accrued) benefit expense	8.7	(9.3)	(9.9)
Total amount recognized in Consolidated Balance Sheets, all in Other liabilities	(14.5)	(15.7)	(15.2)
Amounts recognized in accumulated other comprehensive income (loss) (AOCI):
Prior service cost	0.0	0.0	0.0
Net actuarial loss	(6.5)	(6.4)	(5.3)
Total amount recognized in AOCI	(6.5)	(6.4)	(5.3)
Information for pension plans with an accumulated benefit obligation greater than plan assets:
Projected benefit obligation	14.5	15.7	15.2
Accumulated benefit obligation	14.5	15.7	15.2
Fair value of plan assets	$ 0.0	$ 0.0	$ 0.0