Accelerating Aon United Program - Schedule of Program Costs Incurred (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Restructuring Cost and Reserve [Line Items]
Charges	$ 96	$ 94	$ 188	$ 204
Accelerating Aon United Program
Restructuring Cost and Reserve [Line Items]
Charges	96	94	188	204
Accelerating Aon United Program \| Corporate
Restructuring Cost and Reserve [Line Items]
Charges	83	56	151	143
Risk Capital \| Accelerating Aon United Program \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Charges	14	32	33	51
Human Capital \| Accelerating Aon United Program \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Charges	$ (1)	$ 6	$ 4	$ 10

- 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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