Accelerating Aon United Program - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2024	Sep. 30, 2023	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Restructuring Cost and Reserve [Line Items]
Charges	$ 132		$ 0	$ 251	$ 0
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	$ 132			$ 251