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Acquisitions and Dispositions of Businesses - Schedule of Pro Forma Information (Details) - NFP Acquisition - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2025 | Jun. 30, 2024 | Jun. 30, 2025 | Jun. 30, 2024
Business Combination, Pro Forma Information [Line Items] |  |  |  |
Revenue | $ 3,910 | $ 3,729 | $ 8,528 | $ 8,099
Net income attributable to Aon shareholders | $ 465 | $ 427 | $ 1,401 | $ 1,269

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