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Accelerating Aon United Program - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2025 | Jun. 30, 2024 | Sep. 30, 2023 | Jun. 30, 2025 | Jun. 30, 2024
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Charges | $ 94 | $ 132 |  | $ 204 | $ 251
Accelerating Aon United Program |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Restructuring plan, period |  |  | 3 years |  |
Expected cost | 1,000 |  |  | 1,000 |
Expected cost, cash charges | 900 |  |  | 900 |
Expected cost, non-cash charges | 100 |  |  | 100 |
Charges | 94 | $ 132 |  | 204 | $ 251
Accelerating Aon United Program | Risk Capital |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Expected cost | 220 |  |  | 220 |
Accelerating Aon United Program | Human Capital |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Expected cost | $ 60 |  |  | $ 60 |

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