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