Accelerating Aon United Program - Program Costs Incurred (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Restructuring Cost and Reserve [Line Items]
Accelerating Aon United Program expenses	$ 365	$ 389	$ 135
Accelerating Aon United Program
Restructuring Cost and Reserve [Line Items]
Accelerating Aon United Program expenses	365	389
Accelerating Aon United Program | Corporate
Restructuring Cost and Reserve [Line Items]
Accelerating Aon United Program expenses	267	248
Risk Capital | Accelerating Aon United Program | Operating Segments
Restructuring Cost and Reserve [Line Items]
Accelerating Aon United Program expenses	82	114
Human Capital | Accelerating Aon United Program | Operating Segments
Restructuring Cost and Reserve [Line Items]
Accelerating Aon United Program expenses	$ 16	$ 27