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Acquisitions and Dispositions of Businesses - Other Significant Activity (Details) $ in Billions | Jul. 26, 2021 USD ($)
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Subsequent Event |
Business Acquisition [Line Items] |
Termination fee | $ 1

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- Definition Business Combination, Termination Fees + References No definition available. + Details
Name: | aon_BusinessCombinationTerminationFees
Namespace Prefix: | aon_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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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. + References No definition available. + Details
Name: | us-gaap_BusinessAcquisitionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |