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Pension and Other Postretirement Benefit Plans - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Accumulated benefit obligation |  | $ 26,400 | $ 22,800 |
Employer contributions to defined contribution savings plans |  | $ 166 | $ 149 | $ 136
Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Percentage of Company's pension investments categorized as Level 3 assets (as percent) |  | 4.00% | 4.00% |
Pension Benefits | Level 3 |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Fair value of plan assets |  | $ 942 | $ 860 |
Other Postretirement Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Fair value of plan assets |  | 1,221 | 1,102 | $ 968
Expected contributions to the pension plans and other postretirement benefit plans during next fiscal year |  | 35 |  |
Other Postretirement Benefits | Level 3 |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Fair value of plan assets |  | $ 0 | $ 0 |
United States |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Expected annual standard deviation in returns of the target portfolio which reflects both the equity allocation and the diversification benefits among the asset classes in which the portfolio invests (as percent) |  | 11.00% |  |
Expected rate of return on plan assets (as percent) |  | 7.30% | 8.10% | 8.20%
United States | Minimum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Expected rate of return on plan assets (as percent) |  | 7.00% |  |
United States | Minimum | Forecast |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Expected rate of return on plan assets (as percent) | 6.50% |  |  |
United States | Maximum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Expected rate of return on plan assets (as percent) |  | 7.30% |  |
United States | Maximum | Forecast |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Expected rate of return on plan assets (as percent) | 6.70% |  |  |
United States | U.S. equities | Minimum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation (as percent) |  | 30.00% |  |
United States | U.S. equities | Maximum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation (as percent) |  | 45.00% |  |
United States | International equities | Minimum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation (as percent) |  | 15.00% |  |
United States | International equities | Maximum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation (as percent) |  | 30.00% |  |
United States | Fixed Income Investments | Minimum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation (as percent) |  | 35.00% |  |
United States | Fixed Income Investments | Maximum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation (as percent) |  | 45.00% |  |
United States | Cash And Other Investments | Maximum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Target allocation (as percent) |  | 5.00% |  |
United States | Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Accumulated benefit obligation |  | $ 14,400 | $ 12,800 |
Fair value of plan assets |  | 12,672 | 11,361 | $ 9,648
Expected contributions to the pension plans and other postretirement benefit plans during next fiscal year |  | 300 |  |
United States | Pension Benefits | Level 3 |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Fair value of plan assets |  | 7 | 9 | 13
International | Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Fair value of plan assets |  | 12,049 | $ 10,163 | $ 8,580
Expected contributions to the pension plans and other postretirement benefit plans during next fiscal year |  | $ 170 |  |
Expected rate of return on plan assets (as percent) |  | 4.40% | 4.90% | 5.10%
International | Pension Benefits | Level 3 |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Fair value of plan assets |  | $ 935 | $ 851 | $ 813

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