Pension and Postretirement Benefit Costs (Tables)

6 Months Ended

Jun. 30, 2022

Retirement Benefits [Abstract]

Schedule of Net Benefit Costs

Net periodic pension credit included the following components:

	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
	(Dollars in millions)
Service cost for benefits earned	$	—	$	0.1	$	—	$	0.1
Interest cost on projected benefit obligation	5.4		5.1		10.7		10.2
Expected return on plan assets	(6.0)		(5.7)		(11.9)		(11.4)
Net periodic pension credit	$	(0.6)	$	(0.5)	$	(1.2)	$	(1.1)

Net periodic postretirement benefit credit included the following components:

	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
	(Dollars in millions)
Service cost for benefits earned	$	0.2	$	0.3	$	0.4	$	0.5
Interest cost on accumulated postretirement benefit obligation	1.8		2.9		3.5		5.8
Expected return on plan assets	(0.2)		(0.2)		(0.4)		(0.4)
Amortization of prior service credit	(13.5)		(11.0)		(26.9)		(22.0)
Net periodic postretirement benefit credit	$	(11.7)	$	(8.0)	$	(23.4)	$	(16.1)