Accelerating Aon United Program (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Restructuring Cost and Reserve [Line Items]
Accelerating Aon United Program expenses	$ 6	$ 0	$ 6	$ 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
Accelerating Aon United Program expenses	$ 6		$ 6