Pension and Postretirement Benefit Costs (Tables)

3 Months Ended

Mar. 31, 2019

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 cost (benefit) included the following components:

	Three Months Ended March 31,
	2019			2018
	(Dollars in millions)
Service cost for benefits earned	$	0.5		$	0.6
Interest cost on projected benefit obligation	8.3			7.8
Expected return on plan assets	(7.8		)	(10.7		)
Net periodic pension cost (benefit)	$	1.0		$	(2.3	)

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,
	2019			2018
	(Dollars in millions)
Service cost for benefits earned	$	1.2		$	2.0
Interest cost on accumulated postretirement benefit obligation	6.3			7.1
Expected return on plan assets	(0.1		)	—
Amortization of prior service credit	(2.2		)	—
Net periodic postretirement benefit cost	$	5.2		$	9.1