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Pensions And Other Postretirement Benefits - Contributions and Plan Amendments (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions to defined contribution plans | $ 573 | $ 537 | $ 617
Pension Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Years of service | 30 years |  |
Employer contributions | $ 464 | 615 | 1,700
Pension Plan | Qualified Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Period of time for which there are no mandatory contributions for qualified plans | 5 years |  |
Pension Plan | U.S. |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions | $ 68 | 83 | 76
Pension Plan | U.S. | Nonqualified Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Estimated contributions in next fiscal year | 70 |  |
Pension Plan | U.S. | Qualified Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Mandatory contributions over the next five years | 0 |  |
Pension Plan | Non-U.S. |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions | 396 | 532 | 1,624
Estimated contributions in next fiscal year | 500 |  |
Pension Plan | Canada and United Kingdom |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Mandatory contributions over the next five years | 366 |  |
Other Postretirement Benefits Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions | 387 | 370 |
Other Postretirement Benefits Plan | U.S. |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions | 343 | $ 326 | 325
Pension Plan and Other Postretirement Benefits Plan | U.S. |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Remeasurement decrease due to mortality assumptions | $ 686 |  | $ 264

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