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Derivatives and Hedging - Net Investments in Foreign Operations Risk Management Narrative (Details) - Net Investment Hedging $ in Millions | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2021 EUR (€) | Dec. 31, 2020 EUR (€) | Sep. 30, 2021 USD ($) | Dec. 31, 2020 USD ($)
Derivatives, Fair Value |  |  |  |
European denominated commercial paper | € | € 0 | € 0 |  |
Non-derivative hedging instrument, unrealized gain | $ |  |  | $ 29 | $ 29

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- Definition Non-Derivative Hedging Instrument, Unrealized Gain + References No definition available. + Details
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Namespace Prefix: | aon_
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Balance Type: | credit
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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
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- Definition Nominal or face amount used to calculate payments on a nonderivative instrument. + References No definition available. + Details
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- Details
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