Accelerating Aon United Program - Additional Information (Details) - Accelerating Aon United Program - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2023	Dec. 31, 2025	Dec. 30, 2025
Restructuring Cost and Reserve [Line Items]
Restructuring plan, period	3 years
Expected cost		$ 1,300	$ 1,000
Expected cost, cash charges		1,200
Expected cost, non-cash charges		100
Risk Capital
Restructuring Cost and Reserve [Line Items]
Expected cost		300
Human Capital
Restructuring Cost and Reserve [Line Items]
Expected cost		$ 80