Pensions and Post-Retirement Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

Components of Net Periodic Benefit Cost for Pension Plans and Other Benefit Plans

et periodic pension costs:

	Year Ended December 31,
	Pension Benefits									Other Benefits
	2023			2022			2021			2023			2022			2021
(Dollars in millions)
Service cost	$	1.6		$	1.2		$	1.5		$	0.0		$	0.0		$	0.1
Interest cost		8.2			5.6			5.2			0.3			0.3			0.3
Expected return on plan assets		(7.0	)		(7.7	)		(7.4	)		0.0			0.0			0.0
Amortization of net loss (gain)		2.2			1.8			1.4			(0.6	)		(0.1	)		0.0
Net periodic benefit cost	$	5.0		$	0.9		$	0.7		$	(0.3	)	$	0.2		$	0.4

Schedule of Change in Funded Status of Pension and Post-Retirement Plans

The following table presents the change in the funded status of the pension and post-retirement plans:

	Year Ended December 31,
	Pension Benefits						Other Benefits
	2023			2022			2023			2022
(Dollars in millions)
Change in benefit obligation:
Benefit obligation at beginning of year	$	157.0		$	219.6		$	6.0		$	9.8
Service cost		1.6			1.2			0.0			0.0
Interest cost		8.2			5.6			0.3			0.3
Actuarial (gains) losses		(2.1	)		(51.8	)		0.7			(3.4	)
Settlements		(1.1	)		(1.0	)		0.0			0.0
Currency translation		1.9			(5.8	)		0.0			0.0
Benefits paid		(11.2	)		(10.8	)		(0.8	)		(0.7	)
Benefit obligation at end of year		154.3			157.0			6.2			6.0
Change in plan assets:
Fair value of plan assets at beginning of year		127.4			190.0			0.0			0.0
Actual return on plan assets		9.2			(46.1	)		0.0			0.0
Employer contribution		1.9			0.9			0.8			0.7
Settlements		(1.1	)		(1.0	)		0.0			0.0
Currency translation		1.9			(5.6	)		0.0			0.0
Benefits paid		(11.2	)		(10.8	)		(0.8	)		(0.7	)
Fair value of plan assets at end of year		128.1			127.4			0.0			0.0
Funded status of the plan	$	(26.2	)	$	(29.6	)	$	(6.2	)	$	(6.0	)

Plan Data

	Year Ended December 31,
	Pension Benefits
	2023		2022
(Dollars in millions)
Pension plans with projected benefit obligations     in excess of plan assets:
Benefit obligation	$	152.6	$	154.4
Fair value of plan assets		125.8		124.2
Pension plans with accumulated benefit     obligations in excess of plan assets:
Accumulated benefit obligation	$	152.4	$	154.2
Fair value of plan assets		125.8		124.2

Schedule of Projected Benefit Payments

Benefit payments for pension benefits, which are primarily funded by the pension plan assets, and other benefits, which are funded by general corporate assets, are expected to be paid as follows:

	Pension Benefits		Other Benefits
(Dollars in millions)
2024	$	11.4	$	0.5
2025		11.8		0.5
2026		11.3		0.5
2027		11.2		0.5
2028		11.5		0.5
Next five years		57.3		2.4

Schedule of Weighted-Average Assumptions

Weighted-Average Assumptions

	December 31,
	Pension Benefits						Other Benefits
	2023			2022			2023			2022
Discount rate		5.27	%		5.42	%		5.50	%		5.58	%
Expected return on plan assets		5.62			4.65
Rate of compensation increase		3.28			3.13
Initial medical trend rate								5.40			5.40

Schedule of Weighted Average Asset Allocation for Company's Pension Plans

The weighted average asset allocation for our pension plans by asset category is as follows:

	December 31,
	2023			2022
Debt securities		72	%		52	%
Equity securities		0			20
Other		28			28
		100	%		100	%

Schedule of Pension Plan Assets at Fair Value

The following tables set forth by level, our pension plan assets at fair value, within the fair value hierarchy:

	December 31, 2023
	Quoted prices in active markets for identical assets (Level 1)		Significant observable inputs (Level 2)		Significant unobservable inputs (Level 3)		Total
(Dollars in millions)
U.S. equity securities	$	0.0	$	0.1	$	0.0	$	0.1
International equity securities		0.0		0.4		0.0		0.4
U.S. debt securities		0.0		0.3		0.0		0.3
International debt securities		0.0		0.8		0.0		0.8
Insurance annuity contract and other   investments		0.0		0.4		33.4		33.8
Cash and cash equivalents		0.0		1.5		0.0		1.5
	$	0.0	$	3.5	$	33.4	$	36.9
Investments measured at NAV(1)								91.2
Total assets at fair value							$	128.1
(1) The fair value amounts presented in the table above are intended to permit reconciliations of the fair value hierarchy to the total plan assets.

	December 31, 2022
	Quoted prices in active markets for identical assets (Level 1)		Significant observable inputs (Level 2)		Significant unobservable inputs (Level 3)		Total
(Dollars in millions)
U.S. equity securities	$	0.0	$	4.9	$	0.0	$	4.9
International equity securities		0.0		11.1		0.0	11.1
U.S. debt securities		0.0		39.2		0.0	39.2
International debt securities		0.0	2.6			0.0	2.6
Other investments		0.0	0.5			31.5		32.0
Cash and cash equivalents		0.0		1.6		0.0		1.6
	$	0.0	$	59.9	$	31.5	$	91.4
Investments measured at NAV(1)								36.0
Total assets at fair value							$	127.4
(1) The fair value amounts presented in the table above are intended to permit reconciliations of the fair value hierarchy to the total plan assets.