Accelerating Aon United Program - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Restructuring Cost and Reserve [Line Items]
Charges		$ 389	$ 135	$ 0
Accelerating Aon United Program
Restructuring Cost and Reserve [Line Items]
Restructuring plan, period	3 years
Expected cost		1,000
Expected cost, cash charges		900
Expected cost, non-cash charges		100
Charges		389	$ 135
Accelerating Aon United Program | Risk Capital
Restructuring Cost and Reserve [Line Items]
Expected cost		200
Accelerating Aon United Program | Human Capital
Restructuring Cost and Reserve [Line Items]
Expected cost		$ 50