Employee Benefit Plans (Tables)

6 Months Ended

Jun. 30, 2020

Compensation And Retirement Disclosure [Abstract]

Components of Net Periodic Cost for Defined Benefit Pension Plan and for Postretirement Benefit Plan

The components of net periodic cost for our defined benefit pension plan and for our postretirement benefit plan are included in the following tables:

	Three Months Ended June 30,						Six Months Ended June 30,
	2020			2019			2020			2019
Net Periodic Pension Cost	(Dollars in millions)
Interest cost	$	3.2		$	4.6		$	6.4		$	9.1
Actuarial loss amortization		3.9			3.2			7.8			6.4
Less: Expected return on plan assets		(5.7	)		(5.9	)		(11.4	)		(11.8	)
Net periodic pension cost	$	1.4		$	1.9		$	2.8		$	3.7

	Three Months Ended June 30,						Six Months Ended June 30,
	2020			2019			2020			2019
Net Periodic Postretirement Benefit	(Dollars in millions)
Service benefit	$	—		$	—		$	—		$	—
Interest cost		0.2			0.1			0.3			0.2
Actuarial gain amortization		(0.6	)		(0.6	)		(1.2	)		(1.2	)
Prior service credit amortization		(0.1	)		(0.1	)		(0.2	)		(0.1	)
Net periodic postretirement benefit gain	$	(0.5	)	$	(0.6	)	$	(1.1	)	$	(1.1	)