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Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions |  | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
Dec. 31, 2023 | Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
Pension Benefits |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Contributions by employer |  | $ 16 | $ 26 | $ 67 | $ 73
Estimated future employer contributions in current fiscal year |  | 25 |  | 25 |
United States |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined contribution plan, cost recognized |  | 45 | 45 | 142 | 133
United Kingdom |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined contribution plan, cost recognized |  | $ 39 | $ 39 | $ 130 | $ 120
United Kingdom | Defined Benefit Plan Assets Benchmark | Geographic Concentration Risk |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Concentration risk percentage (as a percent) | 79.00% |  |  |  |
Equity Funds | United States |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target asset allocation, percentage (as a percent) |  | 50.00% |  | 50.00% |
Actual asset allocation percentage of equity (as a percent) |  | 50.00% |  | 50.00% |
Equity Funds | United Kingdom |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target asset allocation, percentage (as a percent) |  | 13.00% |  | 13.00% |
Actual asset allocation percentage of equity (as a percent) |  | 14.00% |  | 14.00% |
Fixed Income Funds | United States |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target asset allocation, percentage (as a percent) |  | 50.00% |  | 50.00% |
Actual asset allocation percentage of equity (as a percent) |  | 50.00% |  | 50.00% |
Fixed Income Funds | United Kingdom |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target asset allocation, percentage (as a percent) |  | 87.00% |  | 87.00% |
Actual asset allocation percentage of equity (as a percent) |  | 86.00% |  | 86.00% |

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