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Pension and Postretirement Benefit Costs (Details) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2017 USD ($) | Apr. 01, 2017 USD ($) | Jun. 30, 2016 USD ($) | Jun. 30, 2016 USD ($) | Apr. 02, 2017 plan
Defined benefit pension plans |  |  |  |  |
Components of net periodic benefit cost |  |  |  |  |
Funding threshold | 80.00% |  |  |  |
Number of non-qualified pension plans prior to reorganization | plan |  |  |  |  | 2
Contributions by employer | $ 0.8 |  |  |  |
Estimated contribution in 2017 to pension plan | 5.9 |  |  |  |
Successor | Defined benefit pension plans |  |  |  |  |
Components of net periodic benefit cost |  |  |  |  |
Service cost for benefits earned | 0.6 |  |  |  |
Interest cost on projected or accumulated postretirement benefit obligation | 9.3 |  |  |  |
Expected return on plan assets | (11.2) |  |  |  |
Amortization of prior service cost and net actuarial loss | 0.0 |  |  |  |
Net periodic pension or postretirement benefit cost | (1.3) |  |  |  |
Successor | Postretirement benefit plans |  |  |  |  |
Components of net periodic benefit cost |  |  |  |  |
Service cost for benefits earned | 2.3 |  |  |  |
Interest cost on projected or accumulated postretirement benefit obligation | 8.3 |  |  |  |
Amortization of prior service cost and net actuarial loss | 0.0 |  |  |  |
Net periodic pension or postretirement benefit cost | $ 10.6 |  |  |  |
Predecessor | Defined benefit pension plans |  |  |  |  |
Components of net periodic benefit cost |  |  |  |  |
Service cost for benefits earned |  | $ 0.6 | $ 0.7 | $ 1.3 |
Interest cost on projected or accumulated postretirement benefit obligation |  | 9.7 | 10.3 | 20.7 |
Expected return on plan assets |  | (11.0) | (11.3) | (22.6) |
Amortization of prior service cost and net actuarial loss |  | 6.4 | 6.3 | 12.5 |
Net periodic pension or postretirement benefit cost |  | 5.7 | 6.0 | 11.9 |
Predecessor | Postretirement benefit plans |  |  |  |  |
Components of net periodic benefit cost |  |  |  |  |
Service cost for benefits earned |  | 2.3 | 2.6 | 5.2 |
Interest cost on projected or accumulated postretirement benefit obligation |  | 8.4 | 8.8 | 17.6 |
Amortization of prior service cost and net actuarial loss |  | 3.2 | 2.3 | 4.7 |
Net periodic pension or postretirement benefit cost |  | $ 13.9 | $ 13.7 | $ 27.5 |

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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of 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)(4) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of contribution received by defined benefit plan from employer which increases plan assets. + 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 (d)(5)(ii) -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 6 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2709-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(iv)(01) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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