Pension and Postretirement Benefit Costs (Tables)

3 Months Ended

Mar. 31, 2020

Defined benefit pension plans

Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]

Schedule of Net Benefit Costs

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

	Three Months Ended March 31,
	2020			2019
	(Dollars in millions)
Service cost for benefits earned	$	—		$	0.5
Interest cost on projected benefit obligation	7.0			8.3
Expected return on plan assets	(7.4		)	(7.8		)
Net periodic pension (benefit) cost	$	(0.4	)	$	1.0

Postretirement benefit plans

Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]

Schedule of Net Benefit Costs

Net periodic postretirement benefit cost included the following components:

	Three Months Ended March 31,
	2020			2019
	(Dollars in millions)
Service cost for benefits earned	$	1.1		$	1.2
Interest cost on accumulated postretirement benefit obligation	5.5			6.3
Expected return on plan assets	(0.4		)	(0.1		)
Amortization of prior service credit	(2.2		)	(2.2		)
Net periodic postretirement benefit cost	$	4.0		$	5.2