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Pension and Savings Plans Change in Benefit Obligation, Plan Assets and Funded Status of Pension Plans (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
Amounts recognized in the consolidated balance sheets: |  |  |  |
Liabilities Subject to Compromise | $ (8,416.7) |  | $ (8,440.2) |
Predecessor |  |  |  |
Change in benefit obligation: |  |  |  |
Actuarial loss |  |  | 32.3 |
Amounts recognized in the consolidated balance sheets: |  |  |  |
Liabilities Subject to Compromise |  |  | (8,440.2) |
Fresh Start Adjustment, Fair Value Adjustment | 0.0 |  | 0.0 | $ 0.0
Predecessor | Pension Plan [Member] |  |  |  |
Change in benefit obligation: |  |  |  |
Projected benefit obligation at beginning of period | 959.3 | $ 936.4 | 939.3 |
Service cost | 0.6 |  | 2.5 | 2.7
Interest cost | 9.7 |  | 41.5 | 40.4
Benefits paid | (15.0) |  | (61.1) |
Actuarial loss | 0.0 |  | (37.1) |
Projected benefit obligation at end of period | 936.4 |  | 959.3 | 939.3
Fair value of plan assets at beginning of period | 773.0 |  | 757.3 |
Actual (loss) return on plan assets | 25.1 |  | 75.7 |
Employer contributions | 0.0 |  | 1.1 |
Benefits paid | (15.0) |  | (61.1) |
Fair value of plan assets at end of period |  |  | 773.0 | $ 757.3
Funded status at end of year | (153.3) |  | (186.3) |
Amounts recognized in the consolidated balance sheets: |  |  |  |
Noncurrent obligation (included in Other noncurrent liabilities) | (153.3) |  | (163.5) |
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Other | 0.0 |  |  |
Liabilities Subject to Compromise |  |  | (22.8) |
Net amount recognized | (153.3) |  | (186.3) |
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement | 0.0 |  | 0.0 |
Fresh Start Adjustment, Fair Value Adjustment | 18.2 |  | 0.0 |
Defined Benefit Plan, Plan Assets, Payment for Settlement | 0.0 |  | $ 0.0 |
Successor |  |  |  |
Change in benefit obligation: |  |  |  |
Projected benefit obligation at beginning of period |  | 803.1 |  |
Service cost |  | 6.9 |  |
Interest cost |  | 24.2 |  |
Benefits paid |  | (29.3) |  |
Actuarial loss |  | (22.0) |  |
Plan amendments |  | 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 |  |
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) |  |
Amounts recognized in the consolidated balance sheets: |  |  |  |
Current obligation (included in Accounts payable and accrued expenses) |  | (53.3) |  |
Liabilities Subject to Compromise |  | 0.0 |  |
Fresh Start Adjustment, Fair Value Adjustment |  | (22.5) |  |
Successor | Pension Plan [Member] |  |  |  |
Change in benefit obligation: |  |  |  |
Projected benefit obligation at beginning of period |  | 936.4 |  |
Service cost |  | 1.6 |  |
Interest cost |  | 28.0 |  |
Benefits paid |  | (45.3) |  |
Actuarial loss |  | (25.3) |  |
Projected benefit obligation at end of period | 936.4 | 874.6 |  |
Fair value of plan assets at beginning of period |  | 783.1 |  |
Actual (loss) return on plan assets |  | 80.1 |  |
Employer contributions |  | 30.1 |  |
Benefits paid |  | (45.3) |  |
Fair value of plan assets at end of period | $ 783.1 | 776.6 |  |
Funded status at end of year |  | (98.0) |  |
Amounts recognized in the consolidated balance sheets: |  |  |  |
Noncurrent obligation (included in Other noncurrent liabilities) |  | 0.0 |  |
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Other |  | (98.0) |  |
Net amount recognized |  | (98.0) |  |
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement |  | 71.4 |  |
Fresh Start Adjustment, Fair Value Adjustment |  | 0.0 |  |
Defined Benefit Plan, Plan Assets, Payment for Settlement |  | $ 71.4 |  |

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