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Postretirement Health Care and Life Insurance Benefits Net Periodic Postretirement Benefit Cost (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Apr. 01, 2017 | Dec. 31, 2017 | Dec. 31, 2019 | Dec. 31, 2018
Components of net periodic postretirement benefit cost |  |  |  |
Net periodic postretirement benefit cost | $ 14.4 | $ 21.9 | $ 19.4 | $ 18.1
Postretirement Health Care and Life Insurance Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Accumulated postretirement benefit obligation at end of period |  | 783.3 | 659.9 | 595.4
Components of net periodic postretirement benefit cost |  |  |  |
Service cost for benefits earned | 2.3 | 6.9 | 4.8 | 8.2
Interest cost on accumulated postretirement benefit obligation | 8.4 | 24.2 | 25.1 | 28.3
Defined Benefit Plan, Expected Return (Loss) on Plan Assets | 0.0 | 0.0 | (0.5) | 0.0
Amortization of prior service credit | (2.3) | 0.0 | (8.7) | 0.0
Amortization of actuarial loss | 5.5 | 0.0 | 0.0 | 0.0
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss), Net | 0.0 | (22.0) | 78.3 | (128.4)
Net periodic postretirement benefit cost | $ 13.9 | $ 9.1 | $ 99.0 | $ (91.9)

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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/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 + Details
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