Pension and Postretirement Benefit Costs (Tables)

6 Months Ended

Jun. 30, 2017

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 included the following components:

	Successor			Predecessor			Successor			Predecessor
	April 2 through June 30, 2017			Three Months Ended June 30, 2016			April 2 through June 30, 2017			January 1 through April 1, 2017			Six Months Ended June 30, 2016
	(Dollars in millions)
Service cost for benefits earned	$	0.6		$	0.7		$	0.6		$	0.6		$	1.3
Interest cost on projected benefit obligation	9.3			10.3			9.3			9.7			20.7
Expected return on plan assets	(11.2		)	(11.3		)	(11.2		)	(11.0		)	(22.6		)
Amortization of prior service cost and net actuarial loss	—			6.3			—			6.4			12.5
Net periodic pension cost	$	(1.3	)	$	6.0		$	(1.3	)	$	5.7		$	11.9

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:

	Successor		Predecessor		Successor		Predecessor
	April 2 through June 30, 2017		Three Months Ended June 30, 2016		April 2 through June 30, 2017		January 1 through April 1, 2017		Six Months Ended June 30, 2016
	(Dollars in millions)
Service cost for benefits earned	$	2.3	$	2.6	$	2.3	$	2.3	$	5.2
Interest cost on accumulated postretirement benefit obligation	8.3		8.8		8.3		8.4		17.6
Amortization of prior service cost and net actuarial loss	—		2.3		—		3.2		4.7
Net periodic postretirement benefit cost	$	10.6	$	13.7	$	10.6	$	13.9	$	27.5