Pension and Postretirement Benefit Costs (Tables)

9 Months Ended

Sep. 30, 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 September 30,						Nine Months Ended September 30,
	2019			2018			2019			2018
	(Dollars in millions)
Service cost for benefits earned	$	0.5		$	0.6		$	1.5		$	1.7
Interest cost on projected benefit obligation	8.4			7.9			25.1			23.6
Expected return on plan assets	(7.9		)	(10.7		)	(23.5		)	(32.1		)
Net periodic pension cost (benefit)	$	1.0		$	(2.2	)	$	3.1		$	(6.8	)

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 September 30,					Nine Months Ended September 30,
	2019			2018		2019			2018
	(Dollars in millions)
Service cost for benefits earned	$	1.2		$	2.1	$	3.6		$	6.2
Interest cost on accumulated postretirement benefit obligation	6.3			7.0		18.9			21.2
Expected return on plan assets	(0.2		)	—		(0.4		)	—
Amortization of prior service credit	(2.2		)	—		(6.6		)	—
Net periodic postretirement benefit cost	$	5.1		$	9.1	$	15.5		$	27.4