Pension and Postretirement Benefit Costs (Tables)

3 Months Ended

Mar. 31, 2021

Retirement Benefits [Abstract]

Schedule of Net Benefit Costs

Net periodic pension benefit included the following components:

	Three Months Ended March 31,
	2021		2020
	(Dollars in millions)
Interest cost on projected benefit obligation	$	5.1	$	7.0
Expected return on plan assets	(5.7)		(7.4)
Net periodic pension benefit	$	(0.6)	$	(0.4)

Net periodic postretirement benefit (benefit) cost included the following components:

	Three Months Ended March 31,
	2021		2020
	(Dollars in millions)
Service cost for benefits earned	$	0.2	$	1.1
Interest cost on accumulated postretirement benefit obligation	2.9		5.5
Expected return on plan assets	(0.2)		(0.4)
Amortization of prior service credit	(11.0)		(2.2)
Net periodic postretirement benefit (benefit) cost	$	(8.1)	$	4.0