Other Defined Benefit Plan Information [Abstract]

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- Definition

Percentage of company's qualified pension plans on a GAAP accounting basis.

+ References

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- Definition

Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan.

+ References

+ Details

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- Definition

Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan.

+ References

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- Definition

Amount of cost recognized for passage of time related to defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(2)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Amount of net periodic benefit cost (credit) for defined benefit plan.

+ References

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- References

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- Definition

Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

+ References

No definition available.

+ Details

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Pension and Postretirement Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Apr. 01, 2017	Sep. 30, 2017	Sep. 30, 2018
Successor
Components of net periodic benefit cost
Net periodic pension (benefit) cost	$ 4.5	$ 6.6		$ 13.2	$ 13.6
Successor \| Defined benefit pension plans
Components of net periodic benefit cost
Service cost for benefits earned	0.6	0.5		1.1	1.7
Interest cost on projected benefit obligation	7.9	9.4		18.7	23.6
Expected return on plan assets	(10.7)	(11.2)		(22.4)	(32.1)
Amortization of prior service cost and net actuarial loss	0.0	0.0		0.0	0.0
Net periodic pension (benefit) cost	$ (2.2)	(1.3)		(2.6)	$ (6.8)
Other Defined Benefit Plan Information [Abstract]
Funding threshold	80.00%				80.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 20.0				$ 62.0
Successor \| Postretirement benefit plans
Components of net periodic benefit cost
Service cost for benefits earned	2.1	2.3		4.6	6.2
Interest cost on projected benefit obligation	7.0	8.2		16.5	21.2
Amortization of prior service cost and net actuarial loss	0.0	0.0		0.0	0.0
Net periodic pension (benefit) cost	$ 9.1	$ 10.5		$ 21.1	$ 27.4
Predecessor
Components of net periodic benefit cost
Net periodic pension (benefit) cost			$ 14.4
Predecessor \| Defined benefit pension plans
Components of net periodic benefit cost
Service cost for benefits earned			0.6
Interest cost on projected benefit obligation			9.7
Expected return on plan assets			(11.0)
Amortization of prior service cost and net actuarial loss			6.4
Net periodic pension (benefit) cost			5.7
Predecessor \| Postretirement benefit plans
Components of net periodic benefit cost
Service cost for benefits earned			2.3
Interest cost on projected benefit obligation			8.4
Amortization of prior service cost and net actuarial loss			3.2
Net periodic pension (benefit) cost			$ 13.9