Accelerating Aon United Program - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2023	Sep. 30, 2026	Sep. 30, 2025
Restructuring Cost and Reserve [Line Items]
Charges	$ 93	$ 32		$ 281	$ 236
Accelerating Aon United Program
Restructuring Cost and Reserve [Line Items]
Restructuring plan, period			3 years
Expected cost	1,300			1,300
Expected cost, cash charges	1,200			1,200
Expected cost, non-cash charges	100			100
Charges	93	$ 32		281	$ 236
Accelerating Aon United Program \| Risk Capital
Restructuring Cost and Reserve [Line Items]
Expected cost	325			325
Accelerating Aon United Program \| Human Capital
Restructuring Cost and Reserve [Line Items]
Expected cost	$ 80			$ 80

- Definition

Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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