Employee Benefits - Benefit Obligations and Funded Status of Pension Plans, OPEB and Salaried VEBAs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Salaried VEBA
Change in benefit obligation:
Obligation at beginning of year	$ 58.9	$ 79.8
Service cost		0.1
Interest cost	2.9	1.9
Prior service cost (credit)	(8.8)
Actuarial loss (gain)	0.4	(16.3)
Benefits paid	(6.5)	(6.6)
Obligation at end of year	46.9	58.9	$ 79.8
Change in plan assets:
Fair market value of plan assets at beginning of year	42.4	59.2
Actual return on assets	6.1	(10.2)
Company contributions	1.1
Benefits paid	(6.5)	(6.6)
Fair market value of plan assets at end of year	43.1	42.4	59.2
Net funded status	(3.8)	(16.5)
Cumulative gain (loss) recognized in Accumulated other comprehensive income:
Accumulated net actuarial gain	5.2	1.7
Prior service cost	(16.0)	(29.7)
Total	(10.8)	(28.0)
Pension Plans
Change in benefit obligation:
Obligation at beginning of year	18.8	20.3
Foreign currency translation adjustment	0.2	(0.5)
Service cost	3.8	5.8	4.1
Interest cost	1.3	0.6	0.5
Prior service cost (credit)	6.6
Actuarial loss (gain)	0.2	(7.1)
Plan participants contributions	0.1	0.1
Benefits paid	(0.5)	(0.4)
Obligation at end of year	30.5	18.8	20.3
Change in plan assets:
Fair market value of plan assets at beginning of year	14.9	9.8
Foreign currency translation adjustment	0.2	(0.5)
Actual return on assets	1.4	(2.6)
Plan participants contributions	0.1	0.1
Company contributions	4.4	8.5
Benefits paid	(0.5)	(0.4)
Fair market value of plan assets at end of year	20.5	14.9	9.8
Net funded status	(10.0)	(3.9)
Cumulative gain (loss) recognized in Accumulated other comprehensive income:
Accumulated net actuarial gain	1.3	2.6
Prior service cost	(6.1)
Total	(4.8)	2.6
Other Postretirement Benefits Plan
Change in benefit obligation:
Obligation at beginning of year	66.4	83.5
Service cost	1.1	1.6	1.1
Interest cost	3.4	2.2	1.7
Actuarial loss (gain)	(0.7)	(20.4)
Plan participants contributions	0.1	0.1
Benefits paid	(1.5)	(0.6)
Obligation at end of year	68.8	66.4	$ 83.5
Change in plan assets:
Plan participants contributions	0.1	0.1
Company contributions	1.4	0.5
Benefits paid	(1.5)	(0.6)
Net funded status	(68.8)	(66.4)
Cumulative gain (loss) recognized in Accumulated other comprehensive income:
Accumulated net actuarial gain	17.4	17.8
Total	$ 17.4	$ 17.8