Pension and Postretirement Benefit Costs (Tables)

3 Months Ended

Mar. 31, 2023

Retirement Benefits [Abstract]

Schedule of Net Benefit Costs

Net periodic pension cost (credit) included the following components:

	Three Months Ended March 31,
	2023		2022
	(Dollars in millions)
Interest cost on projected benefit obligation	$	7.4	$	5.3
Expected return on plan assets	(6.6)		(5.9)
Net periodic pension cost (credit)	$	0.8	$	(0.6)

Net periodic postretirement benefit credit included the following components:

	Three Months Ended March 31,
	2023		2022
	(Dollars in millions)
Service cost for benefits earned	$	0.1	$	0.2
Interest cost on accumulated postretirement benefit obligation	2.5		1.7
Expected return on plan assets	(0.1)		(0.2)
Amortization of prior service credit	(13.4)		(13.4)
Net periodic postretirement benefit credit	$	(10.9)	$	(11.7)