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Accelerating Aon United Program - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2025 | Mar. 31, 2024 | Sep. 30, 2023
Restructuring Cost and Reserve [Line Items] |  |  |
Charges | $ 110 | $ 119 |
Accelerating Aon United Program |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Restructuring plan, period |  |  | 3 years
Expected cost | 1,000 |  |
Expected cost, cash charges | 900 |  |
Expected cost, non-cash charges | 100 |  |
Charges | 110 | $ 119 |
Accelerating Aon United Program | Risk Capital |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Expected cost | 200 |  |
Accelerating Aon United Program | Human Capital |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Expected cost | $ 50 |  |

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