Pension and Postretirement Benefit Costs (Tables)

9 Months Ended

Sep. 30, 2020

Retirement Benefits [Abstract]

Schedule of Net Benefit Costs

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
	(Dollars in millions)
Service cost for benefits earned	$	0.1	$	0.5	$	0.2	$	1.5
Interest cost on projected benefit obligation	7.0		8.4		21.0		25.1
Expected return on plan assets	(7.5)		(7.9)		(22.3)		(23.5)
Net periodic pension (benefit) cost	$	(0.4)	$	1.0	$	(1.1)	$	3.1

Net periodic postretirement benefit cost included the following components:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
	(Dollars in millions)
Service cost for benefits earned	$	1.1	$	1.2	$	3.3	$	3.6
Interest cost on accumulated postretirement benefit obligation	5.4		6.3		16.3		18.9
Expected return on plan assets	(0.3)		(0.2)		(1.1)		(0.4)
Amortization of prior service credit	(2.2)		(2.2)		(6.6)		(6.6)
Net actuarial loss	13.0		—		13.0		—
Net periodic postretirement benefit cost	$	17.0	$	5.1	$	24.9	$	15.5