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Amount of increase (decrease) in benefit obligation of defined benefit plan from change in terms of existing plan or initiation of new plan.

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Postretirement Health Care and Life Insurance Benefits Reconciliation of Postretirement Plans' Funded Status to the Balance Sheet (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Apr. 01, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Successor
Reconciled amount of plans funded status
Projected benefit obligation at beginning of period		$ 803.1
Service cost		6.9
Interest cost		24.2
Participant contributions		0.4
Plan changes		0.0
Benefits paid		(29.3)
Actuarial loss		(22.0)
Other		0.0
Projected benefit obligation at end of period	$ 803.1	783.3
Fair value of plan assets at beginning of period		0.0
Employer contributions		28.9
Participant contributions		0.4
Benefits paid		(29.3)
Fair value of plan assets at end of period	0.0	0.0
Funded status at end of year		(783.3)
Less current portion (included in Accounts payable and accrued expenses)		(53.3)
Successor \| Postretirement Health Care and Life Insurance Benefits [Member]
Reconciled amount of plans funded status
Service cost		6.9
Interest cost		24.2
Actuarial loss		(22.0)
Noncurrent obligation (included in Accrued postretirement benefit costs)		(730.0)
Predecessor
Reconciled amount of plans funded status
Actuarial loss			$ 32.3
Other	(7.1)		0.0
Predecessor \| Postretirement Health Care and Life Insurance Benefits [Member]
Reconciled amount of plans funded status
Projected benefit obligation at beginning of period	812.1	803.1	776.1
Service cost	2.3		10.4	$ 11.2
Interest cost	8.4		34.5	33.8
Participant contributions	0.2		0.6
Plan changes	0.0		7.2
Benefits paid	(12.8)		(49.0)
Actuarial loss	0.0		0.0	0.0
Projected benefit obligation at end of period	803.1		812.1	776.1
Fair value of plan assets at beginning of period	0.0	$ 0.0	0.0
Employer contributions	12.6		48.4
Participant contributions	0.2		0.6
Benefits paid	(12.8)		(49.0)
Fair value of plan assets at end of period	0.0		0.0	$ 0.0
Funded status at end of year	(803.1)		(812.1)
Less current portion (included in Accounts payable and accrued expenses)	(56.1)		(55.8)
Noncurrent obligation (included in Accrued postretirement benefit costs)	$ (747.0)		$ (756.3)