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Postretirement Health Care and Life Insurance Benefits Reconciliation of Postretirement Plans' Funded Status to the Balance Sheet (Details) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Apr. 01, 2017 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2019 USD ($) years | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) years
Postretirement Health Care and Life Insurance Benefits |  |  |  |  |
Change in benefit obligation: |  |  |  |  |
Accumulated postretirement benefit obligation at beginning of period |  |  | $ 595.4 | $ 783.3 |
Service cost | $ 2.3 | $ 6.9 | 4.8 | 8.2 |
Interest cost | 8.4 | 24.2 | 25.1 | 28.3 |
Participant contributions |  |  | 2.3 | 0.5 |
Plan amendments |  |  | 0.0 | (51.7) |
Benefits paid |  |  | (47.7) | (44.8) |
Actuarial loss (gain) |  |  | 80.0 | (128.4) |
Accumulated postretirement benefit obligation at end of period |  | 783.3 | 659.9 | 595.4 | $ 783.3
Change in plan assets: |  |  |  |  |
Fair value of plan assets at beginning of period |  |  | 15.0 | 0.0 |
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) |  |  | 2.2 | 0.0 |
Employer contributions |  |  | 62.4 | 59.3 |
Participant contributions |  |  | 2.3 | 0.5 |
Benefits paid and administrative fees (net of Medicare Part D reimbursements) |  |  | (47.7) | (44.8) |
Fair value of plan assets at end of period |  | 0.0 | 34.2 | 15.0 | $ 0.0
Funded status at end of period |  |  | (625.7) | (580.4) |
Less: Current portion (included in “Accounts payable and accrued expenses”) |  |  | 32.3 | 32.7 |
Noncurrent obligation (included in “Accrued postretirement benefit costs”) |  |  | $ (593.4) | (547.7) |
Defined Benefit Plan, Amortization Period | years |  |  | 5.9 |  | 10.3
Annual Benefits | Postretirement Health Care and Life Insurance Benefits |  |  |  |  |
Change in benefit obligation: |  |  |  |  |
Plan amendments |  |  |  | 50.2 |
Limitation of eligibility based on age and service criteria | Postretirement Health Care and Life Insurance Benefits |  |  |  |  |
Change in benefit obligation: |  |  |  |  |
Plan amendments |  |  |  | 1.5 |
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] |  |  |  |  |
Change in plan assets: |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax | $ 0.0 | $ 0.0 | $ 0.0 | $ 44.6 |

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