Accelerating Aon United Program - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Restructuring Cost and Reserve [Line Items]
Accelerating Aon United Program expenses		$ 135	$ 0	$ 0
Accelerating Aon United Program
Restructuring Cost and Reserve [Line Items]
Restructuring plan, period	3 years
Expected cost	$ 1,000	1,000
Charges	900	900
Non-cash charges	$ 100	100
Accelerating Aon United Program expenses		$ 135