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Pension and Other Postretirement Benefits - Funding and Cash Flows and Defined Contribution Plans (Details) - USD ($) $ in Millions |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | ---
Nov. 01, 2016 | Apr. 30, 2019 | Mar. 31, 2018 | Apr. 30, 2017 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |
Payment for pension benefits |  |  |  |  | $ 227 | $ 268 |
Payment for pension benefit plan in excess of minimum required |  |  |  |  | 25 | 53 |
Contribution next fiscal year |  |  |  |  | 140 |  |
Aggregate cash contribution to pension plan | $ 150 |  |  |  |  |  |
Cash contribution term to pension plan | 30 months |  |  |  |  |  |
Payment for pension and other postretirement benefits |  | $ 34 | $ 66 | $ 50 |  |  |
Defined Benefit Plan, Expected Future Benefit Payment [Abstract] |  |  |  |  |  |  |
Expenses related to defined contribution plan |  |  |  |  | 73 | $ 87 | $ 85
Pension benefits paid |  |  |  |  |  |  |
Defined Benefit Plan, Expected Future Benefit Payment [Abstract] |  |  |  |  |  |  |
2021 |  |  |  |  | 168 |  |
2022 |  |  |  |  | 169 |  |
2023 |  |  |  |  | 164 |  |
2024 |  |  |  |  | 160 |  |
2025 |  |  |  |  | 158 |  |
2026 - 2030 |  |  |  |  | 728 |  |
Total benefit payments |  |  |  |  | 1,547 |  |
Gross Other post- retirement benefits |  |  |  |  |  |  |
Defined Benefit Plan, Expected Future Benefit Payment [Abstract] |  |  |  |  |  |  |
2021 |  |  |  |  | 17 |  |
2022 |  |  |  |  | 16 |  |
2023 |  |  |  |  | 16 |  |
2024 |  |  |  |  | 15 |  |
2025 |  |  |  |  | 15 |  |
2026 - 2030 |  |  |  |  | 67 |  |
Total benefit payments |  |  |  |  | 146 |  |
Less Medicare Part D subsidy receipts |  |  |  |  |  |  |
Defined Benefit Plan, Expected Future Benefit Payment [Abstract] |  |  |  |  |  |  |
2021 |  |  |  |  | 1 |  |
2022 |  |  |  |  | 1 |  |
2023 |  |  |  |  | 1 |  |
2024 |  |  |  |  | 1 |  |
2025 |  |  |  |  | 1 |  |
2026 - 2030 |  |  |  |  | 6 |  |
Less Medicare Part D subsidy receipts |  |  |  |  | 11 |  |
Net Other post- retirement benefits |  |  |  |  |  |  |
Defined Benefit Plan, Expected Future Benefit Payment [Abstract] |  |  |  |  |  |  |
2021 |  |  |  |  | 16 |  |
2022 |  |  |  |  | 15 |  |
2023 |  |  |  |  | 15 |  |
2024 |  |  |  |  | 14 |  |
2025 |  |  |  |  | 14 |  |
2026 - 2030 |  |  |  |  | 61 |  |
Total benefit payments |  |  |  |  | 135 |  |
United States |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |
Contribution next fiscal year |  |  |  |  | $ 130 |  |

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