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Revenue from Contracts with Clients - Narrative (Details) | 12 Months Ended
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Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2020
Revenue from Contract with Customer [Abstract] |  |  |
Total revenues (percentage) | 5.50% | 5.00% | 0.90%
Term of risk management consulting contracts | 6 months |  |

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