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Pension and Other Postretirement Benefits - Schedule of Benefit Payments Expected to be Paid and Expected Medicare Part D Subsidy Receipts (Detail) $ in Millions | Dec. 31, 2017 USD ($)
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Pension benefits |
Defined Benefit Plan Disclosure [Line Items] |
2018 | $ 435
2019 | 440
2020 | 440
2021 | 445
2022 | 450
Thereafter | 2,265
Total benefit payments | 4,475
Gross Other post- retirement benefits |
Defined Benefit Plan Disclosure [Line Items] |
2018 | 90
2019 | 90
2020 | 90
2021 | 90
2022 | 90
Thereafter | 335
Total benefit payments | 785
Medicare Part D subsidy receipts |
Defined Benefit Plan Disclosure [Line Items] |
2018 | 5
2019 | 5
2020 | 5
2021 | 5
2022 | 5
Thereafter | 25
Total benefit payments | 50
Net Other post- retirement benefits |
Defined Benefit Plan Disclosure [Line Items] |
2018 | 85
2019 | 85
2020 | 85
2021 | 85
2022 | 85
Thereafter | 310
Total benefit payments | $ 735

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