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