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Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions |  | 3 Months Ended
--- | --- | ---
Dec. 31, 2024 | Mar. 31, 2025 | Mar. 31, 2024
Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Contributions by employer |  | $ 18 | $ 24
Estimated future employer contributions in current fiscal year |  | 62 |
United States |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution plan, cost recognized |  | 56 | 49
United Kingdom |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution plan, cost recognized |  | $ 56 | $ 52
United Kingdom | Pension and Postretirement Benefit Plan, Defined Benefit | Geographic Concentration Risk |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Concentration risk percentage (as a percent) | 78.00% |  |
Equity Funds | United States |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target asset allocation, percentage (as a percent) |  | 50.00% |
Actual asset allocation percentage of equity (as a percent) |  | 50.00% |
Equity Funds | United Kingdom |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target asset allocation, percentage (as a percent) |  | 12.00% |
Actual asset allocation percentage of equity (as a percent) |  | 10.00% |
Fixed Income Funds | United States |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target asset allocation, percentage (as a percent) |  | 50.00% |
Actual asset allocation percentage of equity (as a percent) |  | 50.00% |
Fixed Income Funds | United Kingdom |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target asset allocation, percentage (as a percent) |  | 88.00% |
Actual asset allocation percentage of equity (as a percent) |  | 90.00% |

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