Accelerating Aon United Program - Program Costs Incurred (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Restructuring Cost and Reserve [Line Items]
Total	$ 92	$ 110
Accelerating Aon United Program
Restructuring Cost and Reserve [Line Items]
Total	92	110
Accelerating Aon United Program | Corporate
Restructuring Cost and Reserve [Line Items]
Total	68	87
Risk Capital | Accelerating Aon United Program | Operating Segments
Restructuring Cost and Reserve [Line Items]
Total	19	19
Human Capital | Accelerating Aon United Program | Operating Segments
Restructuring Cost and Reserve [Line Items]
Total	$ 5	$ 4