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Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions |  | 9 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items] |  |  |
Pension, post-retirement and post-employment benefits | $ 2,336 | $ 2,163 |
Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Contributions by employer |  | 81 |
Estimated future employer contributions in current fiscal year |  | 63 |
Jardine Lloyd Thompson Group plc |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Pension, post-retirement and post-employment benefits | 255 |  |
Pension, post-retirement and post-employment liabilities | 1,003 |  |
Pension, post-retirement and post-employment plan assets | $ 748 |  |
United States |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution plan, cost recognized |  | 110 | $ 106
United Kingdom |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution plan, cost recognized |  | $ 94 | $ 74
United Kingdom | Non-U.S. Plans | Geographic Concentration Risk |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Concentration risk percentage | 81.00% |  |
Equity Funds | United States |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target asset allocation, percentage |  | 64.00% |
Actual asset allocation percentage of equity |  | 63.00% |
Equity Funds | United Kingdom |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target asset allocation, percentage |  | 33.00% |
Actual asset allocation percentage of equity |  | 33.00% |
Fixed Income Funds | United States |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target asset allocation, percentage |  | 36.00% |
Actual asset allocation percentage of equity |  | 37.00% |
Fixed Income Funds | United Kingdom |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target asset allocation, percentage |  | 67.00% |
Actual asset allocation percentage of equity |  | 67.00% |

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