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Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions |  | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
Dec. 31, 2022 | Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022
Pension Benefits |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Contributions by employer |  | $ 26 | $ 28 | $ 73 | $ 141
Estimated future employer contributions in current fiscal year |  | 35 |  | 35 |
United States |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined contribution plan, cost recognized |  | 45 | 39 | 133 | 122
United Kingdom |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined contribution plan, cost recognized |  | $ 39 | $ 31 | $ 120 | $ 108
United Kingdom | Non-U.S. Plans | Geographic Concentration Risk |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Concentration risk percentage | 79.00% |  |  |  |
Equity Funds | United States |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target asset allocation, percentage |  | 50.00% |  | 50.00% |
Actual asset allocation percentage of equity |  | 48.00% |  | 48.00% |
Equity Funds | United Kingdom |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target asset allocation, percentage |  | 14.00% |  | 14.00% |
Actual asset allocation percentage of equity |  | 14.00% |  | 14.00% |
Fixed Income Funds | United States |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target asset allocation, percentage |  | 50.00% |  | 50.00% |
Actual asset allocation percentage of equity |  | 52.00% |  | 52.00% |
Fixed Income Funds | United Kingdom |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target asset allocation, percentage |  | 86.00% |  | 86.00% |
Actual asset allocation percentage of equity |  | 86.00% |  | 86.00% |

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