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Accelerating Aon United Program - Schedule of Program Costs Incurred (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Restructuring Cost and Reserve [Line Items] |  |  |  |
Charges | $ 32 | $ 69 | $ 236 | $ 320
Accelerating Aon United Program |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Charges | 32 | 69 | 236 | 320
Accelerating Aon United Program | Corporate |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Charges | 36 | 54 | 179 | 190
Risk Capital | Accelerating Aon United Program | Operating Segments |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Charges | (3) | 11 | 48 | 103
Human Capital | Accelerating Aon United Program | Operating Segments |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Charges | $ (1) | $ 4 | $ 9 | $ 27

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