<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2021 Workiva-->
<!--r:09573f37-1728-42bf-9c80-6c02fd3e47df,g:80061792-7849-49b1-a506-3ab8a3d66766-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:aon="http://www.aon.com/20201231" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:nonnum="http://www.xbrl.org/dtr/type/non-numeric" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:num="http://www.xbrl.org/dtr/type/numeric" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.aon.com/20201231">
  <xs:import namespace="http://fasb.org/srt/2020-01-31" schemaLocation="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd"/>
  <xs:import namespace="http://fasb.org/us-gaap/2020-01-31" schemaLocation="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd"/>
  <xs:import namespace="http://www.w3.org/1999/xlink" schemaLocation="http://www.xbrl.org/2003/xlink-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/dtr/type/non-numeric" schemaLocation="http://www.xbrl.org/dtr/type/nonNumeric-2009-12-16.xsd"/>
  <xs:import namespace="http://www.xbrl.org/dtr/type/numeric" schemaLocation="http://www.xbrl.org/dtr/type/numeric-2009-12-16.xsd"/>
  <xs:import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/country/2020-01-31" schemaLocation="https://xbrl.sec.gov/country/2020/country-2020-01-31.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/dei/2020-01-31" schemaLocation="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd"/>
  <xs:annotation>
    <xs:appinfo>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="aon-20201231_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="aon-20201231_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="aon-20201231_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="aon-20201231_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:type="simple"/>
      <link:roleType id="Cover" roleURI="http://www.aon.com/role/Cover">
        <link:definition>000010001 - Document - Cover</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsofIncome" roleURI="http://www.aon.com/role/ConsolidatedStatementsofIncome">
        <link:definition>100010002 - Statement - Consolidated Statements of Income</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsofComprehensiveIncome" roleURI="http://www.aon.com/role/ConsolidatedStatementsofComprehensiveIncome">
        <link:definition>100020003 - Statement - Consolidated Statements of Comprehensive Income</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsofFinancialPosition" roleURI="http://www.aon.com/role/ConsolidatedStatementsofFinancialPosition">
        <link:definition>100030004 - Statement - Consolidated Statements of Financial Position</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsofFinancialPositionParenthetical" roleURI="http://www.aon.com/role/ConsolidatedStatementsofFinancialPositionParenthetical">
        <link:definition>100040005 - Statement - Consolidated Statements of Financial Position (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsofShareholdersEquity" roleURI="http://www.aon.com/role/ConsolidatedStatementsofShareholdersEquity">
        <link:definition>100050006 - Statement - Consolidated Statements of Shareholders' Equity</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsofShareholdersEquityParenthetical" roleURI="http://www.aon.com/role/ConsolidatedStatementsofShareholdersEquityParenthetical">
        <link:definition>100060007 - Statement - Consolidated Statements of Shareholders' Equity (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsofCashFlows" roleURI="http://www.aon.com/role/ConsolidatedStatementsofCashFlows">
        <link:definition>100070008 - Statement - Consolidated Statements of Cash Flows</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BasisofPresentation" roleURI="http://www.aon.com/role/BasisofPresentation">
        <link:definition>210011001 - Disclosure - Basis of Presentation</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BasisofPresentationDetails" roleURI="http://www.aon.com/role/BasisofPresentationDetails">
        <link:definition>240024001 - Disclosure - Basis of Presentation (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPrinciplesandPractices" roleURI="http://www.aon.com/role/SummaryofSignificantAccountingPrinciplesandPractices">
        <link:definition>210031002 - Disclosure - Summary of Significant Accounting Principles and Practices</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPrinciplesandPracticesPolicies" roleURI="http://www.aon.com/role/SummaryofSignificantAccountingPrinciplesandPracticesPolicies">
        <link:definition>220042001 - Disclosure - Summary of Significant Accounting Principles and Practices (Policies)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPrinciplesandPracticesTables" roleURI="http://www.aon.com/role/SummaryofSignificantAccountingPrinciplesandPracticesTables">
        <link:definition>230053001 - Disclosure - Summary of Significant Accounting Principles and Practices (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPrinciplesandPracticesAdditionalInformationDetails" roleURI="http://www.aon.com/role/SummaryofSignificantAccountingPrinciplesandPracticesAdditionalInformationDetails">
        <link:definition>240064002 - Disclosure - Summary of Significant Accounting Principles and Practices - Additional Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenuefromContractswithCustomers" roleURI="http://www.aon.com/role/RevenuefromContractswithCustomers">
        <link:definition>210071003 - Disclosure - Revenue from Contracts with Customers</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenuefromContractswithCustomersTables" roleURI="http://www.aon.com/role/RevenuefromContractswithCustomersTables">
        <link:definition>230083002 - Disclosure - Revenue from Contracts with Customers (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenuefromContractswithCustomersDisaggregationofRevenueDetails" roleURI="http://www.aon.com/role/RevenuefromContractswithCustomersDisaggregationofRevenueDetails">
        <link:definition>240094003 - Disclosure - Revenue from Contracts with Customers - Disaggregation of Revenue (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenuefromContractswithCustomersContractAssetsRollforwardDetails" roleURI="http://www.aon.com/role/RevenuefromContractswithCustomersContractAssetsRollforwardDetails">
        <link:definition>240104004 - Disclosure - Revenue from Contracts with Customers - Contract Assets Rollforward (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="OtherFinancialData" roleURI="http://www.aon.com/role/OtherFinancialData">
        <link:definition>210111004 - Disclosure - Other Financial Data</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="OtherFinancialDataTables" roleURI="http://www.aon.com/role/OtherFinancialDataTables">
        <link:definition>230123003 - Disclosure - Other Financial Data (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="OtherFinancialDataScheduleofOtherIncomeExpenseDetails" roleURI="http://www.aon.com/role/OtherFinancialDataScheduleofOtherIncomeExpenseDetails">
        <link:definition>240134005 - Disclosure - Other Financial Data - Schedule of Other Income (Expense) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="OtherFinancialDataScheduleofAllowanceforDoubtfulAccountsDetails" roleURI="http://www.aon.com/role/OtherFinancialDataScheduleofAllowanceforDoubtfulAccountsDetails">
        <link:definition>240144006 - Disclosure - Other Financial Data - Schedule of Allowance for Doubtful Accounts (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="OtherFinancialDataScheduleofOtherCurrentAssetsDetails" roleURI="http://www.aon.com/role/OtherFinancialDataScheduleofOtherCurrentAssetsDetails">
        <link:definition>240154007 - Disclosure - Other Financial Data - Schedule of Other Current Assets (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="OtherFinancialDataComponentsofFixedAssetsNetDetails" roleURI="http://www.aon.com/role/OtherFinancialDataComponentsofFixedAssetsNetDetails">
        <link:definition>240164008 - Disclosure - Other Financial Data - Components of Fixed Assets, Net (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="OtherFinancialDataScheduleofOtherNoncurrentAssetsDetails" roleURI="http://www.aon.com/role/OtherFinancialDataScheduleofOtherNoncurrentAssetsDetails">
        <link:definition>240174009 - Disclosure - Other Financial Data - Schedule of Other Non-current Assets (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="OtherFinancialDataScheduleofOtherCurrentLiabilitiesDetails" roleURI="http://www.aon.com/role/OtherFinancialDataScheduleofOtherCurrentLiabilitiesDetails">
        <link:definition>240184010 - Disclosure - Other Financial Data - Schedule of Other Current Liabilities (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="OtherFinancialDataScheduleofOtherNoncurrentLiabilitiesDetails" roleURI="http://www.aon.com/role/OtherFinancialDataScheduleofOtherNoncurrentLiabilitiesDetails">
        <link:definition>240194011 - Disclosure - Other Financial Data - Schedule of Other Non-current Liabilities (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Restructuring" roleURI="http://www.aon.com/role/Restructuring">
        <link:definition>210201005 - Disclosure - Restructuring</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RestructuringDetails" roleURI="http://www.aon.com/role/RestructuringDetails">
        <link:definition>240214012 - Disclosure - Restructuring (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionsandDispositionsofBusinesses" roleURI="http://www.aon.com/role/AcquisitionsandDispositionsofBusinesses">
        <link:definition>210221006 - Disclosure - Acquisitions and Dispositions of Businesses</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionsandDispositionsofBusinessesTables" roleURI="http://www.aon.com/role/AcquisitionsandDispositionsofBusinessesTables">
        <link:definition>230233004 - Disclosure - Acquisitions and Dispositions of Businesses (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionsandDispositionsofBusinessesCompletedAcquisitionsNarrativeDetails" roleURI="http://www.aon.com/role/AcquisitionsandDispositionsofBusinessesCompletedAcquisitionsNarrativeDetails">
        <link:definition>240244013 - Disclosure - Acquisitions and Dispositions of Businesses - Completed Acquisitions Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionsandDispositionsofBusinessesScheduleofNetAssetsAcquiredDetails" roleURI="http://www.aon.com/role/AcquisitionsandDispositionsofBusinessesScheduleofNetAssetsAcquiredDetails">
        <link:definition>240254014 - Disclosure - Acquisitions and Dispositions of Businesses - Schedule of Net Assets Acquired (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionsandDispositionsofBusinessesCompletedDispositionsDetails" roleURI="http://www.aon.com/role/AcquisitionsandDispositionsofBusinessesCompletedDispositionsDetails">
        <link:definition>240264015 - Disclosure - Acquisitions and Dispositions of Businesses - Completed Dispositions (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillandOtherIntangibleAssets" roleURI="http://www.aon.com/role/GoodwillandOtherIntangibleAssets">
        <link:definition>210271007 - Disclosure - Goodwill and Other Intangible Assets</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillandOtherIntangibleAssetsTables" roleURI="http://www.aon.com/role/GoodwillandOtherIntangibleAssetsTables">
        <link:definition>230283005 - Disclosure - Goodwill and Other Intangible Assets (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillandOtherIntangibleAssetsScheduleofchangesinthenetcarryingamountofgoodwillDetails" roleURI="http://www.aon.com/role/GoodwillandOtherIntangibleAssetsScheduleofchangesinthenetcarryingamountofgoodwillDetails">
        <link:definition>240294016 - Disclosure - Goodwill and Other Intangible Assets - Schedule of changes in the net carrying amount of goodwill (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillandOtherIntangibleAssetsScheduleofotherintangibleassetsbyassetclassDetails" roleURI="http://www.aon.com/role/GoodwillandOtherIntangibleAssetsScheduleofotherintangibleassetsbyassetclassDetails">
        <link:definition>240304017 - Disclosure - Goodwill and Other Intangible Assets - Schedule of other intangible assets by asset class (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillandOtherIntangibleAssetsScheduleofestimatedfutureamortizationexpenseonintangibleassetsDetails" roleURI="http://www.aon.com/role/GoodwillandOtherIntangibleAssetsScheduleofestimatedfutureamortizationexpenseonintangibleassetsDetails">
        <link:definition>240314018 - Disclosure - Goodwill and Other Intangible Assets - Schedule of estimated future amortization expense on intangible assets (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Debt" roleURI="http://www.aon.com/role/Debt">
        <link:definition>210321008 - Disclosure - Debt</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DebtTables" roleURI="http://www.aon.com/role/DebtTables">
        <link:definition>230333006 - Disclosure - Debt (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DebtSummaryofoutstandingdebtDetails" roleURI="http://www.aon.com/role/DebtSummaryofoutstandingdebtDetails">
        <link:definition>240344019 - Disclosure - Debt - Summary of outstanding debt (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DebtNarrativeDetails" roleURI="http://www.aon.com/role/DebtNarrativeDetails">
        <link:definition>240354020 - Disclosure - Debt - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DebtRepaymentsoflongtermdebtDetails" roleURI="http://www.aon.com/role/DebtRepaymentsoflongtermdebtDetails">
        <link:definition>240364021 - Disclosure - Debt - Repayments of long-term debt (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DebtScheduleofCommercialPaperDetails" roleURI="http://www.aon.com/role/DebtScheduleofCommercialPaperDetails">
        <link:definition>240374022 - Disclosure - Debt - Schedule of Commercial Paper (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeaseCommitments" roleURI="http://www.aon.com/role/LeaseCommitments">
        <link:definition>210381009 - Disclosure - Lease Commitments</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeaseCommitmentsTables" roleURI="http://www.aon.com/role/LeaseCommitmentsTables">
        <link:definition>230393007 - Disclosure - Lease Commitments (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeaseCommitmentsAssetsandLiabilitiesofLesseeDetails" roleURI="http://www.aon.com/role/LeaseCommitmentsAssetsandLiabilitiesofLesseeDetails">
        <link:definition>240404023 - Disclosure - Lease Commitments - Assets and Liabilities of Lessee (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeaseCommitmentsLeaseCostsDetails" roleURI="http://www.aon.com/role/LeaseCommitmentsLeaseCostsDetails">
        <link:definition>240414024 - Disclosure - Lease Commitments - Lease Costs (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeaseCommitmentsLeaseTermsandAssumptionsDetails" roleURI="http://www.aon.com/role/LeaseCommitmentsLeaseTermsandAssumptionsDetails">
        <link:definition>240424025 - Disclosure - Lease Commitments - Lease Terms and Assumptions (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeaseCommitmentsCashFlowofLesseeDetails" roleURI="http://www.aon.com/role/LeaseCommitmentsCashFlowofLesseeDetails">
        <link:definition>240434026 - Disclosure - Lease Commitments - Cash Flow of Lessee (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeaseCommitmentsLeaseMaturityDetails" roleURI="http://www.aon.com/role/LeaseCommitmentsLeaseMaturityDetails">
        <link:definition>240444027 - Disclosure - Lease Commitments - Lease Maturity (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxes" roleURI="http://www.aon.com/role/IncomeTaxes">
        <link:definition>210451010 - Disclosure - Income Taxes</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesTables" roleURI="http://www.aon.com/role/IncomeTaxesTables">
        <link:definition>230463008 - Disclosure - Income Taxes (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesIncomefromcontinuingoperationsbeforeincometaxDetails" roleURI="http://www.aon.com/role/IncomeTaxesIncomefromcontinuingoperationsbeforeincometaxDetails">
        <link:definition>240474028 - Disclosure - Income Taxes - Income from continuing operations before income tax (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesNarrativeDetails" roleURI="http://www.aon.com/role/IncomeTaxesNarrativeDetails">
        <link:definition>240484029 - Disclosure - Income Taxes - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesReconciliationoftheincometaxprovisionsbasedontheUSstatutorycorporatetaxratetotheprovisionsreflectedintheConsolidatedFinancialStatementsDetails" roleURI="http://www.aon.com/role/IncomeTaxesReconciliationoftheincometaxprovisionsbasedontheUSstatutorycorporatetaxratetotheprovisionsreflectedintheConsolidatedFinancialStatementsDetails">
        <link:definition>240494030 - Disclosure - Income Taxes - Reconciliation of the income tax provisions based on the U.S. statutory corporate tax rate to the provisions reflected in the Consolidated Financial Statements (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesComponentsofAonsdeferredtaxassetsandliabilitiesDetails" roleURI="http://www.aon.com/role/IncomeTaxesComponentsofAonsdeferredtaxassetsandliabilitiesDetails">
        <link:definition>240504031 - Disclosure - Income Taxes - Components of Aon's deferred tax assets and liabilities (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesDeferredincometaxesassetsandliabilitiesnettedbyjurisdictionasclassifiedintheConsolidatedStatementsofFinancialPositionDetails" roleURI="http://www.aon.com/role/IncomeTaxesDeferredincometaxesassetsandliabilitiesnettedbyjurisdictionasclassifiedintheConsolidatedStatementsofFinancialPositionDetails">
        <link:definition>240514032 - Disclosure - Income Taxes - Deferred income taxes (assets and liabilities netted by jurisdiction) as classified in the Consolidated Statements of Financial Position (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesOperatingLossCarryforwardsDetails" roleURI="http://www.aon.com/role/IncomeTaxesOperatingLossCarryforwardsDetails">
        <link:definition>240524033 - Disclosure - Income Taxes Operating Loss Carryforwards (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesReconciliationofthebeginningandendingamountofunrecognizedtaxbenefitsDetails" roleURI="http://www.aon.com/role/IncomeTaxesReconciliationofthebeginningandendingamountofunrecognizedtaxbenefitsDetails">
        <link:definition>240534034 - Disclosure - Income Taxes - Reconciliation of the beginning and ending amount of unrecognized tax benefits (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareholdersEquity" roleURI="http://www.aon.com/role/ShareholdersEquity">
        <link:definition>210541011 - Disclosure - Shareholders' Equity</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareholdersEquityTables" roleURI="http://www.aon.com/role/ShareholdersEquityTables">
        <link:definition>230553009 - Disclosure - Shareholders' Equity (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareholdersEquityDistributableReservesNarrativeDetails" roleURI="http://www.aon.com/role/ShareholdersEquityDistributableReservesNarrativeDetails">
        <link:definition>240564035 - Disclosure - Shareholders' Equity - Distributable Reserves Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareholdersEquityOrdinarySharesDetails" roleURI="http://www.aon.com/role/ShareholdersEquityOrdinarySharesDetails">
        <link:definition>240574036 - Disclosure - Shareholders' Equity - Ordinary Shares (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareholdersEquityScheduleofweightedaveragesharesoutstandingDetails" roleURI="http://www.aon.com/role/ShareholdersEquityScheduleofweightedaveragesharesoutstandingDetails">
        <link:definition>240584037 - Disclosure - Shareholders' Equity - Schedule of weighted average shares outstanding (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareholdersEquityComponentsofAccumulatedothercomprehensivelossnetofrelatedtaxDetails" roleURI="http://www.aon.com/role/ShareholdersEquityComponentsofAccumulatedothercomprehensivelossnetofrelatedtaxDetails">
        <link:definition>240594038 - Disclosure - Shareholders' Equity - Components of Accumulated other comprehensive loss, net of related tax (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefits" roleURI="http://www.aon.com/role/EmployeeBenefits">
        <link:definition>210601012 - Disclosure - Employee Benefits</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsTables" roleURI="http://www.aon.com/role/EmployeeBenefitsTables">
        <link:definition>230613010 - Disclosure - Employee Benefits (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsScheduleofexpenserecognizedinCompensationandbenefitintheConsolidatedStatementsofIncomeDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsScheduleofexpenserecognizedinCompensationandbenefitintheConsolidatedStatementsofIncomeDetails">
        <link:definition>240624039 - Disclosure - Employee Benefits - Schedule of expense recognized in Compensation and benefit in the Consolidated Statements of Income (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsPensionPlansNarrativeDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsPensionPlansNarrativeDetails">
        <link:definition>240634040 - Disclosure - Employee Benefits - Pension Plans Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsReconciliationofthechangesinthebenefitobligationsandfairvalueofassetsandastatementofthefundedstatusDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsReconciliationofthechangesinthebenefitobligationsandfairvalueofassetsandastatementofthefundedstatusDetails">
        <link:definition>240644041 - Disclosure - Employee Benefits - Reconciliation of the changes in the benefit obligations and fair value of assets and a statement of the funded status (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsAmountsrecognizedintheConsolidatedStatementsofFinancialPositionDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsAmountsrecognizedintheConsolidatedStatementsofFinancialPositionDetails">
        <link:definition>240654042 - Disclosure - Employee Benefits - Amounts recognized in the Consolidated Statements of Financial Position (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsAmountsrecognizedinAccumulatedothercomprehensivelossthathavenotyetbeenrecognizedDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsAmountsrecognizedinAccumulatedothercomprehensivelossthathavenotyetbeenrecognizedDetails">
        <link:definition>240664043 - Disclosure - Employee Benefits - Amounts recognized in Accumulated other comprehensive loss that have not yet been recognized (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsComponentsofnetperiodicbenefitcostDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsComponentsofnetperiodicbenefitcostDetails">
        <link:definition>240674044 - Disclosure - Employee Benefits - Components of net periodic benefit cost (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsWeightedaverageassumptionsusedtodeterminefuturebenefitobligationsDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsWeightedaverageassumptionsusedtodeterminefuturebenefitobligationsDetails">
        <link:definition>240684045 - Disclosure - Employee Benefits - Weighted-average assumptions used to determine future benefit obligations (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsWeightedaverageassumptionsusedtodeterminethenetperiodicbenefitcostDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsWeightedaverageassumptionsusedtodeterminethenetperiodicbenefitcostDetails">
        <link:definition>240694046 - Disclosure - Employee Benefits - Weighted-average assumptions used to determine the net periodic benefit cost (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsExpectedReturnonPlanAssetsNarrativeDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsExpectedReturnonPlanAssetsNarrativeDetails">
        <link:definition>240704047 - Disclosure - Employee Benefits - Expected Return on Plan Assets Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsScheduleofFairValueofUSPlanAssetsDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsScheduleofFairValueofUSPlanAssetsDetails">
        <link:definition>240714048 - Disclosure - Employee Benefits - Schedule of Fair Value of U.S Plan Assets (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsScheduleofFairValueofUKPlanAssetsDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsScheduleofFairValueofUKPlanAssetsDetails">
        <link:definition>240724049 - Disclosure - Employee Benefits - Schedule of Fair Value of U.K. Plan Assets (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsScheduleofchangesinLevel3fairvalueforUKPensionPlansDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsScheduleofchangesinLevel3fairvalueforUKPensionPlansDetails">
        <link:definition>240734050 - Disclosure - Employee Benefits - Schedule of changes in Level 3 fair value for U.K. Pension Plans (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsScheduleofFairValueofOtherPlanAssetsDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsScheduleofFairValueofOtherPlanAssetsDetails">
        <link:definition>240744051 - Disclosure - Employee Benefits - Schedule of Fair Value of Other Plan Assets (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsInvestmentPolicyandStrategyNarrativeDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsInvestmentPolicyandStrategyNarrativeDetails">
        <link:definition>240754052 - Disclosure - Employee Benefits - Investment Policy and Strategy Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsCashFlowsNarrativeDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsCashFlowsNarrativeDetails">
        <link:definition>240764053 - Disclosure - Employee Benefits - Cash Flows Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsEstimatedFutureBenefitPaymentsDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsEstimatedFutureBenefitPaymentsDetails">
        <link:definition>240774054 - Disclosure - Employee Benefits - Estimated Future Benefit Payments (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsOverviewoftheaccumulatedbenefitobligationfairvalueofplanassetsfundedstatusandnetamountrecognizedforUSandCanadianOtherPostRetirementBenefitsDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsOverviewoftheaccumulatedbenefitobligationfairvalueofplanassetsfundedstatusandnetamountrecognizedforUSandCanadianOtherPostRetirementBenefitsDetails">
        <link:definition>240784055 - Disclosure - Employee Benefits - Overview of the accumulated benefit obligation, fair value of plan assets, funded status and net amount recognized for U.S. and Canadian Other Post-Retirement Benefits (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsScheduleofOtherinformationrelatedtoCompanysotherpostretirementplansDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsScheduleofOtherinformationrelatedtoCompanysotherpostretirementplansDetails">
        <link:definition>240794056 - Disclosure - Employee Benefits - Schedule of Other information related to Company's other post-retirement plan's (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitsUSandCanadianOtherPostRetirementBenefitsNarrativeDetails" roleURI="http://www.aon.com/role/EmployeeBenefitsUSandCanadianOtherPostRetirementBenefitsNarrativeDetails">
        <link:definition>240804057 - Disclosure - Employee Benefits - U.S. and Canadian Other Post-Retirement Benefits Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationPlans" roleURI="http://www.aon.com/role/ShareBasedCompensationPlans">
        <link:definition>210811013 - Disclosure - Share-Based Compensation Plans</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationPlansTables" roleURI="http://www.aon.com/role/ShareBasedCompensationPlansTables">
        <link:definition>230823011 - Disclosure - Share-Based Compensation Plans (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationPlansSharebasedcompensationexpenserecognizedincontinuingoperationsDetails" roleURI="http://www.aon.com/role/ShareBasedCompensationPlansSharebasedcompensationexpenserecognizedincontinuingoperationsDetails">
        <link:definition>240834058 - Disclosure - Share-Based Compensation Plans - Share-based compensation expense recognized in continuing operations (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationPlansRestrictedShareUnitsNarrativeDetails" roleURI="http://www.aon.com/role/ShareBasedCompensationPlansRestrictedShareUnitsNarrativeDetails">
        <link:definition>240844059 - Disclosure - Share-Based Compensation Plans - Restricted Share Units Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationPlansSummaryofthestatusoftheCompanysRSUsDetails" roleURI="http://www.aon.com/role/ShareBasedCompensationPlansSummaryofthestatusoftheCompanysRSUsDetails">
        <link:definition>240854060 - Disclosure - Share-Based Compensation Plans - Summary of the status of the Company's RSUs (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationPlansPerformanceShareAwardsNarrativeDetails" roleURI="http://www.aon.com/role/ShareBasedCompensationPlansPerformanceShareAwardsNarrativeDetails">
        <link:definition>240864061 - Disclosure - Share-Based Compensation Plans - Performance Share Awards Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationPlansScheduleofPerformancebasedplansDetails" roleURI="http://www.aon.com/role/ShareBasedCompensationPlansScheduleofPerformancebasedplansDetails">
        <link:definition>240874062 - Disclosure - Share-Based Compensation Plans - Schedule of Performance-based plans (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DerivativesandHedging" roleURI="http://www.aon.com/role/DerivativesandHedging">
        <link:definition>210881014 - Disclosure - Derivatives and Hedging</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DerivativesandHedgingTables" roleURI="http://www.aon.com/role/DerivativesandHedgingTables">
        <link:definition>230893012 - Disclosure - Derivatives and Hedging (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DerivativesandHedgingNarrativeDetails" roleURI="http://www.aon.com/role/DerivativesandHedgingNarrativeDetails">
        <link:definition>240904063 - Disclosure - Derivatives and Hedging - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DerivativesandHedgingNotionalandfairvaluesofderivativeinstrumentsDetails" roleURI="http://www.aon.com/role/DerivativesandHedgingNotionalandfairvaluesofderivativeinstrumentsDetails">
        <link:definition>240914064 - Disclosure - Derivatives and Hedging - Notional and fair values of derivative instruments (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DerivativesandHedgingScheduleofamountsofderivativegainslossesrecognizedintheConsolidatedFinancialStatementsDetails" roleURI="http://www.aon.com/role/DerivativesandHedgingScheduleofamountsofderivativegainslossesrecognizedintheConsolidatedFinancialStatementsDetails">
        <link:definition>240924065 - Disclosure - Derivatives and Hedging - Schedule of amounts of derivative gains (losses) recognized in the Consolidated Financial Statements (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurementsandFinancialInstruments" roleURI="http://www.aon.com/role/FairValueMeasurementsandFinancialInstruments">
        <link:definition>210931015 - Disclosure - Fair Value Measurements and Financial Instruments</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurementsandFinancialInstrumentsTables" roleURI="http://www.aon.com/role/FairValueMeasurementsandFinancialInstrumentsTables">
        <link:definition>230943013 - Disclosure - Fair Value Measurements and Financial Instruments (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurementsandFinancialInstrumentsScheduleofassetsandliabilitiesthataremeasuredatfairvalueonarecurringbasisDetails" roleURI="http://www.aon.com/role/FairValueMeasurementsandFinancialInstrumentsScheduleofassetsandliabilitiesthataremeasuredatfairvalueonarecurringbasisDetails">
        <link:definition>240954066 - Disclosure - Fair Value Measurements and Financial Instruments - Schedule of assets and liabilities that are measured at fair value on a recurring basis (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurementsandFinancialInstrumentsNarrativeDetails" roleURI="http://www.aon.com/role/FairValueMeasurementsandFinancialInstrumentsNarrativeDetails">
        <link:definition>240964067 - Disclosure - Fair Value Measurements and Financial Instruments - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurementsandFinancialInstrumentsScheduleoffinancialinstrumentswherethecarryingamountsandfairvaluesdifferDetails" roleURI="http://www.aon.com/role/FairValueMeasurementsandFinancialInstrumentsScheduleoffinancialinstrumentswherethecarryingamountsandfairvaluesdifferDetails">
        <link:definition>240974068 - Disclosure - Fair Value Measurements and Financial Instruments - Schedule of financial instruments where the carrying amounts and fair values differ (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ClaimsLawsuitsandOtherContingencies" roleURI="http://www.aon.com/role/ClaimsLawsuitsandOtherContingencies">
        <link:definition>210981016 - Disclosure - Claims, Lawsuits and Other Contingencies</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ClaimsLawsuitsandOtherContingenciesLegalNarrativeDetails" roleURI="http://www.aon.com/role/ClaimsLawsuitsandOtherContingenciesLegalNarrativeDetails">
        <link:definition>240994069 - Disclosure - Claims, Lawsuits, and Other Contingencies - Legal Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ClaimsLawsuitsandOtherContingenciesGuaranteesandIndemnificationsNarrativeDetails" roleURI="http://www.aon.com/role/ClaimsLawsuitsandOtherContingenciesGuaranteesandIndemnificationsNarrativeDetails">
        <link:definition>241004070 - Disclosure - Claims, Lawsuits, and Other Contingencies - Guarantees and Indemnifications Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ClaimsLawsuitsandOtherContingenciesLettersofCreditNarrativeDetails" roleURI="http://www.aon.com/role/ClaimsLawsuitsandOtherContingenciesLettersofCreditNarrativeDetails">
        <link:definition>241014071 - Disclosure - Claims, Lawsuits, and Other Contingencies - Letters of Credit Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ClaimsLawsuitsandOtherContingenciesPremiumPaymentsDetails" roleURI="http://www.aon.com/role/ClaimsLawsuitsandOtherContingenciesPremiumPaymentsDetails">
        <link:definition>241024072 - Disclosure - Claims, Lawsuits, and Other Contingencies - Premium Payments (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentInformation" roleURI="http://www.aon.com/role/SegmentInformation">
        <link:definition>211031017 - Disclosure - Segment Information</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentInformationTables" roleURI="http://www.aon.com/role/SegmentInformationTables">
        <link:definition>231043014 - Disclosure - Segment Information (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentInformationNarrativeDetails" roleURI="http://www.aon.com/role/SegmentInformationNarrativeDetails">
        <link:definition>241054073 - Disclosure - Segment Information - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentInformationScheduleofconsolidatednoncurrentassetsbygeographicareaDetails" roleURI="http://www.aon.com/role/SegmentInformationScheduleofconsolidatednoncurrentassetsbygeographicareaDetails">
        <link:definition>241064074 - Disclosure - Segment Information - Schedule of consolidated non-current assets by geographic area (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
    </xs:appinfo>
  </xs:annotation>
  <xs:element id="aon_FiduciaryAssetsAndLiabilitiesAbstract" abstract="true" name="FiduciaryAssetsAndLiabilitiesAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_OtherGeneralExpenses" abstract="false" name="OtherGeneralExpenses" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_SummaryOfSignificantAccountingPoliciesLineItems" abstract="true" name="SummaryOfSignificantAccountingPoliciesLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_GuaranteesOfAonPlcs4600SeniorNotesDue2044Member" abstract="true" name="GuaranteesOfAonPlcs4600SeniorNotesDue2044Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_EquityInvestmentsPooledFundsMember" abstract="true" name="EquityInvestmentsPooledFundsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_FinancingAndOperatingLeaseLiabilityNetOfSubleaseIncome" abstract="false" name="FinancingAndOperatingLeaseLiabilityNetOfSubleaseIncome" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_OperatingLeaseAndFinanceLeaseRightofUseAsset" abstract="false" name="OperatingLeaseAndFinanceLeaseRightofUseAsset" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_FinancingAndOperatingLeaseLiabilityPaymentsNetOfSubleaseIncomeDue" abstract="false" name="FinancingAndOperatingLeaseLiabilityPaymentsNetOfSubleaseIncomeDue" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_DefinedBenefitPlanNetPeriodicBenefitCostBeforeRecognizedNetGainLossDuetoSettlementsandCurtailments" abstract="false" name="DefinedBenefitPlanNetPeriodicBenefitCostBeforeRecognizedNetGainLossDuetoSettlementsandCurtailments" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_CashCashEquivalentsAndShortTermInvestmentsPolicyTextBlock" abstract="false" name="CashCashEquivalentsAndShortTermInvestmentsPolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType"/>
  <xs:element id="aon_EmployeerelatedLiabilitiesNoncurrent" abstract="false" name="EmployeerelatedLiabilitiesNoncurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_IncomeTaxAuthorityTable" abstract="true" name="IncomeTaxAuthorityTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="aon_USCommercialPaperProgramMember" abstract="true" name="USCommercialPaperProgramMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_GuaranteesOfAonPlcs4000SeniorNotesDue2023Member" abstract="true" name="GuaranteesOfAonPlcs4000SeniorNotesDue2023Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_FinancingAndOperatingLeaseLiabilityPaymentsNetOfSubleaseIncomeDueYearThree" abstract="false" name="FinancingAndOperatingLeaseLiabilityPaymentsNetOfSubleaseIncomeDueYearThree" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_AmortizationAndImpairmentOfIntangibleAssetsMember" abstract="true" name="AmortizationAndImpairmentOfIntangibleAssetsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_BusinessCombinationsandDiscontinuedOperationsandDisposalGroupsAbstract" abstract="true" name="BusinessCombinationsandDiscontinuedOperationsandDisposalGroupsAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_ReinsuranceMember" abstract="true" name="ReinsuranceMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_NumberofRevenueLines" abstract="false" name="NumberofRevenueLines" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="aon_LeadershipPerformancePlanCycle20162018Member" abstract="true" name="LeadershipPerformancePlanCycle20162018Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_A4.50SeniorNotesDueDecember2028Member" abstract="true" name="A4.50SeniorNotesDueDecember2028Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_IncomeTaxHolidayIncomeTaxBenefits" abstract="false" name="IncomeTaxHolidayIncomeTaxBenefits" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_FiduciaryLiabilities" abstract="false" name="FiduciaryLiabilities" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_ScheduleOfPropertyPlantAndEquipmentComponentsTableTextBlock" abstract="false" name="ScheduleOfPropertyPlantAndEquipmentComponentsTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType"/>
  <xs:element id="aon_CapitalizedCostToObtainCustomerContractsMember" abstract="true" name="CapitalizedCostToObtainCustomerContractsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_LesseeWeightedaverageRemainingLeaseTermAbstract" abstract="true" name="LesseeWeightedaverageRemainingLeaseTermAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_CommonStockExchangeRatioRelatedToReorganization" abstract="false" name="CommonStockExchangeRatioRelatedToReorganization" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="aon_NotesDueat2043at4.45PercentMember" abstract="true" name="NotesDueat2043at4.45PercentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_InterestCarryforward" abstract="false" name="InterestCarryforward" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_CapitalizedContractCostForeignCurrencyAndOtherAdjustmentsNet" abstract="false" name="CapitalizedContractCostForeignCurrencyAndOtherAdjustmentsNet" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_ShortTermDebtAverageOutstandingAmountWeightedAverageInterestRate" abstract="false" name="ShortTermDebtAverageOutstandingAmountWeightedAverageInterestRate" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="num:percentItemType"/>
  <xs:element id="aon_OtherFinancialDataAbstract" abstract="true" name="OtherFinancialDataAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAfterAccumulatedDepreciationandAmortization" abstract="false" name="PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAfterAccumulatedDepreciationandAmortization" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_DefinedBenefitPlanPercentageOfTotalPensionObligations" abstract="false" name="DefinedBenefitPlanPercentageOfTotalPensionObligations" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="num:percentItemType"/>
  <xs:element id="aon_SharebasedCompensationArrangementbySharebasedPaymentAwardVestingConditionsPeriod" abstract="false" name="SharebasedCompensationArrangementbySharebasedPaymentAwardVestingConditionsPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="aon_GainLossOnSaleofBusinessAndInvestmentsNet" abstract="false" name="GainLossOnSaleofBusinessAndInvestmentsNet" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_OtherInvestmentsPooledFundsMember" abstract="true" name="OtherInvestmentsPooledFundsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_AssetsAndLiabilitiesOfLesseeTableTextBlock" abstract="false" name="AssetsAndLiabilitiesOfLesseeTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType"/>
  <xs:element id="aon_ScheduleOfDeferredTaxAssetsAndLiabilitiesNettedByJurisdictionTableTextBlock" abstract="false" name="ScheduleOfDeferredTaxAssetsAndLiabilitiesNettedByJurisdictionTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType"/>
  <xs:element id="aon_NumberOfDispositions" abstract="false" name="NumberOfDispositions" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="aon_CapitalizedContractCostAdditions" abstract="false" name="CapitalizedContractCostAdditions" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_DeferredTaxAssetsLeaseGuarantees" abstract="false" name="DeferredTaxAssetsLeaseGuarantees" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_LeadershipPerformancePlanCycle20152017Member" abstract="true" name="LeadershipPerformancePlanCycle20152017Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_LeasesMaturityAbstract" abstract="true" name="LeasesMaturityAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_LossContingencyDamagesSoughtValueOptionTwo" abstract="false" name="LossContingencyDamagesSoughtValueOptionTwo" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_UnamortizedExpenseOnPerformanceBasedPlans" abstract="false" name="UnamortizedExpenseOnPerformanceBasedPlans" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_CompensationandBenefitsMember" abstract="true" name="CompensationandBenefitsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_ContractWithCustomerLiabilityIncludingNewContractRevenueRecognized" abstract="false" name="ContractWithCustomerLiabilityIncludingNewContractRevenueRecognized" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedPercent" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedPercent" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="num:percentItemType"/>
  <xs:element id="aon_LesseeWeightedAverageDiscountRateAbstract" abstract="true" name="LesseeWeightedAverageDiscountRateAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_NumberOfCreditFacilities" abstract="false" name="NumberOfCreditFacilities" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="aon_ScheduleofAccountsNotesLoansandFinancingReceivableAllowanceforDoubtfulAccountsTableTextBlock" abstract="false" name="ScheduleofAccountsNotesLoansandFinancingReceivableAllowanceforDoubtfulAccountsTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType"/>
  <xs:element id="aon_LossContingencyInvestmentLossesSufferedByPlaintiff" abstract="false" name="LossContingencyInvestmentLossesSufferedByPlaintiff" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_DataSolutionsMember" abstract="true" name="DataSolutionsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_FinancingAndOperatingLeaseLiabilityPaymentsNetOfSubleaseIncomeDueYearTwo" abstract="false" name="FinancingAndOperatingLeaseLiabilityPaymentsNetOfSubleaseIncomeDueYearTwo" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_OperatingLeaseRightOfUseAssetAmortization" abstract="false" name="OperatingLeaseRightOfUseAssetAmortization" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAcquiredIncludingGoodwill" abstract="false" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAcquiredIncludingGoodwill" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_FivePointZeroZeroPercentSeniorNotesDueTwentyTwentyMember" abstract="true" name="FivePointZeroZeroPercentSeniorNotesDueTwentyTwentyMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_DeferredTaxAssetsAccruedInterest" abstract="false" name="DeferredTaxAssetsAccruedInterest" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_EuropeanMultiCurrencyCommercialPaperProgramMember" abstract="true" name="EuropeanMultiCurrencyCommercialPaperProgramMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_FinancingAndOperatingLeaseLiabilityPaymentsNetOfSubleaseIncomeDueYearFour" abstract="false" name="FinancingAndOperatingLeaseLiabilityPaymentsNetOfSubleaseIncomeDueYearFour" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_OperatingAndFinanceLeaseLiability" abstract="false" name="OperatingAndFinanceLeaseLiability" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_FinancingAndOperatingLeaseLiabilityPaymentsNetOfSubleaseIncomeDueAfterYearFive" abstract="false" name="FinancingAndOperatingLeaseLiabilityPaymentsNetOfSubleaseIncomeDueAfterYearFive" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_NumberOfPerformanceMetricsMeasured" abstract="false" name="NumberOfPerformanceMetricsMeasured" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="aon_EmployeeStockPurchasePlanMember" abstract="true" name="EmployeeStockPurchasePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_FinancingAndOperatingLeaseLiabilityPaymentsNetOfSubleaseIncomeDueYearFive" abstract="false" name="FinancingAndOperatingLeaseLiabilityPaymentsNetOfSubleaseIncomeDueYearFive" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_RealEstateAndRealEstateInvestmentTrustMember" abstract="true" name="RealEstateAndRealEstateInvestmentTrustMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_OperatingLeaseAndFinanceLeaseLiabilityCurrent" abstract="false" name="OperatingLeaseAndFinanceLeaseLiabilityCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_GuaranteesOfAonPlcs3875SeniorNotesDue2025Member" abstract="true" name="GuaranteesOfAonPlcs3875SeniorNotesDue2025Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_RetirementMember" abstract="true" name="RetirementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_LossContingencyDamagesSoughtValueOptionThree" abstract="false" name="LossContingencyDamagesSoughtValueOptionThree" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_ChristchurchCityCouncilMember" abstract="true" name="ChristchurchCityCouncilMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_IncomeTaxAuthorityLineItems" abstract="true" name="IncomeTaxAuthorityLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_MoneyMarketFundsAndOtherHighlyLiquidDebtSecuritiesMember" abstract="true" name="MoneyMarketFundsAndOtherHighlyLiquidDebtSecuritiesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_TRIUMGmbHInsuranceBrokerMember" abstract="true" name="TRIUMGmbHInsuranceBrokerMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_FinanceAndOperatingLeaseLiabilityPaymentsNetOfSubleaseIncomeDueYearOne" abstract="false" name="FinanceAndOperatingLeaseLiabilityPaymentsNetOfSubleaseIncomeDueYearOne" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_A2019And2020AcquisitionsMember" abstract="true" name="A2019And2020AcquisitionsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_A280SeniorNotesDueMay2030Member" abstract="true" name="A280SeniorNotesDueMay2030Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_AmericasOtherthanUnitedStatesMember" abstract="true" name="AmericasOtherthanUnitedStatesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_CustomerRelatedAndContractBasedMember" abstract="true" name="CustomerRelatedAndContractBasedMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_PCAdvisoryMember" abstract="true" name="PCAdvisoryMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_GuaranteesOfAonPlcs3500SeniorNotesDue2024Member" abstract="true" name="GuaranteesOfAonPlcs3500SeniorNotesDue2024Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_LossContingencyDamagesSoughtValueOptionOne" abstract="false" name="LossContingencyDamagesSoughtValueOptionOne" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_RestrictedCashOperatingFunds" abstract="false" name="RestrictedCashOperatingFunds" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_MaximumAverageMaturityOfForeignCurrencyDerivatives" abstract="false" name="MaximumAverageMaturityOfForeignCurrencyDerivatives" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="aon_A3.50NotesdueJune2024Member" abstract="true" name="A3.50NotesdueJune2024Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuable" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="aon_FinancingAndOperatingLeaseLiabilityNetOfSubleaseIncomeUndiscountedExcessAmount" abstract="false" name="FinancingAndOperatingLeaseLiabilityNetOfSubleaseIncomeUndiscountedExcessAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_NoncashLeaseActivitiesAbstract" abstract="true" name="NoncashLeaseActivitiesAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_EquityDerivativeMember" abstract="true" name="EquityDerivativeMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_ShareRepurchaseProgramOf2017Member" abstract="true" name="ShareRepurchaseProgramOf2017Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_FourPointSevenFivePercentSeniorNotesDueTwentyFortyFiveMember" abstract="true" name="FourPointSevenFivePercentSeniorNotesDueTwentyFortyFiveMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_IncreaseDecreaseInFiduciaryLiabilities" abstract="false" name="IncreaseDecreaseInFiduciaryLiabilities" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseTransactionCostsPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationNondeductibleExpenseTransactionCostsPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="aon_A2.875notesdue2026Member" abstract="true" name="A2.875notesdue2026Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_LineOfCreditFacilityMaximumBorrowingCapacityIncreaseDecrease" abstract="false" name="LineOfCreditFacilityMaximumBorrowingCapacityIncreaseDecrease" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_LeadershipPerformancePlanCycle20172019Member" abstract="true" name="LeadershipPerformancePlanCycle20172019Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_GuaranteesOfAonPlcs4750SeniorNotesDue2045Member" abstract="true" name="GuaranteesOfAonPlcs4750SeniorNotesDue2045Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_Noncashpaymentoflongtermdebtnet" abstract="false" name="Noncashpaymentoflongtermdebtnet" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_FiniteLivedIntangibleAssetAbstract" abstract="true" name="FiniteLivedIntangibleAssetAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_A4.00SeniorNotesDueNovember2023Member" abstract="true" name="A4.00SeniorNotesDueNovember2023Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_FarmingtonAdministrativeServicesLLCMember" abstract="true" name="FarmingtonAdministrativeServicesLLCMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_GuaranteesOfAonPlcs4450SeniorNotesDue2043Member" abstract="true" name="GuaranteesOfAonPlcs4450SeniorNotesDue2043Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_BasisMoneyMarketFundsAndHighlyLiquidSecuritiesFairValueDisclosure" abstract="false" name="BasisMoneyMarketFundsAndHighlyLiquidSecuritiesFairValueDisclosure" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_SummaryOfSignificantAccountingPoliciesTable" abstract="true" name="SummaryOfSignificantAccountingPoliciesTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="aon_SeniorNotes4.25PercentDue2042Member" abstract="true" name="SeniorNotes4.25PercentDue2042Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_FiduciaryAssets" abstract="false" name="FiduciaryAssets" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_CytelligenceIncMember" abstract="true" name="CytelligenceIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_CoverWalletIncMember" abstract="true" name="CoverWalletIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_CreditFacilityExpiringOctober2023Member" abstract="true" name="CreditFacilityExpiringOctober2023Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_DeferredTaxLiabilitiesIntangibleAssetsAndPropertyPlantAndEquipment" abstract="false" name="DeferredTaxLiabilitiesIntangibleAssetsAndPropertyPlantAndEquipment" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_EffectiveIncomeTaxRateReconciliationDeferredTaxAdjustmentsIncludingStatutoryRateChangesPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationDeferredTaxAdjustmentsIncludingStatutoryRateChangesPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="num:percentItemType"/>
  <xs:element id="aon_OtherTaxAssetsCurrent" abstract="false" name="OtherTaxAssetsCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_TreasuryStockValueAcquiredCostMethodIncludingAssociatedAcquisitionCosts" abstract="false" name="TreasuryStockValueAcquiredCostMethodIncludingAssociatedAcquisitionCosts" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_GuaranteesOfAonPlcs2875SeniorNotesDue2026Member" abstract="true" name="GuaranteesOfAonPlcs2875SeniorNotesDue2026Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_AssimediaSAMember" abstract="true" name="AssimediaSAMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_CashPaidForLeasesAbstract" abstract="true" name="CashPaidForLeasesAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_GovernmentBondSecuritiesMember" abstract="true" name="GovernmentBondSecuritiesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_CapitalLossCarryforwards" abstract="false" name="CapitalLossCarryforwards" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_DeferredTaxAssetsNetOperatingAndCapitalLossCarryforwardsAndTaxCreditCarryforwards" abstract="false" name="DeferredTaxAssetsNetOperatingAndCapitalLossCarryforwardsAndTaxCreditCarryforwards" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_OrdinaryShareProgramsTable" abstract="true" name="OrdinaryShareProgramsTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="aon_AccountsReceivableAllowanceForCreditLossForeignCurrencyTranslationAndOther" abstract="false" name="AccountsReceivableAllowanceForCreditLossForeignCurrencyTranslationAndOther" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_AmortizationAndImpairmentOfIntangibleAssets" abstract="false" name="AmortizationAndImpairmentOfIntangibleAssets" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_IncreaseDecreaseInFiduciaryReceivables" abstract="false" name="IncreaseDecreaseInFiduciaryReceivables" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_HealthMember" abstract="true" name="HealthMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationUnderlyingPriceInflation" abstract="false" name="DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationUnderlyingPriceInflation" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="num:percentItemType"/>
  <xs:element id="aon_DeferredTaxLiabilitiesLeaseRightofUseAsset" abstract="false" name="DeferredTaxLiabilitiesLeaseRightofUseAsset" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_CommonStockProgramsLineItems" abstract="true" name="CommonStockProgramsLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_OtherGeneralExpensesMember" abstract="true" name="OtherGeneralExpensesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_NEBCMember" abstract="true" name="NEBCMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_DefinedBenefitPlanMarketRelatedValue" abstract="false" name="DefinedBenefitPlanMarketRelatedValue" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_JuniorSubordinatedDeferrableInterestDebentures8.205PercentDue2027Member" abstract="true" name="JuniorSubordinatedDeferrableInterestDebentures8.205PercentDue2027Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_CashandCashEquivalentsandShortTermInvestments" abstract="false" name="CashandCashEquivalentsandShortTermInvestments" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_FatalPlainCrashInNovember2016Member" abstract="true" name="FatalPlainCrashInNovember2016Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_DefinedBenefitPlanPercentageofMedicalSupplementPlan" abstract="false" name="DefinedBenefitPlanPercentageofMedicalSupplementPlan" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="num:percentItemType"/>
  <xs:element id="aon_MarketingTechnologyAndOtherMember" abstract="true" name="MarketingTechnologyAndOtherMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_CapitalizedCostToFulfillCustomerContractsMember" abstract="true" name="CapitalizedCostToFulfillCustomerContractsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_CurrentLeaseLiabilitiesAbstract" abstract="true" name="CurrentLeaseLiabilitiesAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_A3.75SeniorNotesDueMay22029Member" abstract="true" name="A3.75SeniorNotesDueMay22029Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_EffectiveIncomeTaxRateReconciliationCapitalLossesPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationCapitalLossesPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="aon_GuaranteesOfAonPlcs4250SeniorNotesDue2042Member" abstract="true" name="GuaranteesOfAonPlcs4250SeniorNotesDue2042Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_FixedIncomeInvestmentsPooledFundsMember" abstract="true" name="FixedIncomeInvestmentsPooledFundsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_ScheduleOfOtherPostretirementBenefitsOtherInformationTableTextBlock" abstract="false" name="ScheduleOfOtherPostretirementBenefitsOtherInformationTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType"/>
  <xs:element id="aon_AviationandAerospaceBrokingIndustryMember" abstract="true" name="AviationandAerospaceBrokingIndustryMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_A4.60SeniorNotesDueJune2044Member" abstract="true" name="A4.60SeniorNotesDueJune2044Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_GovernmentAndAgencyBondsMember" abstract="true" name="GovernmentAndAgencyBondsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_ShareRepurchaseProgramOf2012Member" abstract="true" name="ShareRepurchaseProgramOf2012Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_A5.00SeniorNotesDueSeptember2020Member" abstract="true" name="A5.00SeniorNotesDueSeptember2020Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_FurnitureFixturesAndEquipmentMember" abstract="true" name="FurnitureFixturesAndEquipmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_TwoPointEightZeroPercentSeniorNotesDueTwentyTwentyOneMember" abstract="true" name="TwoPointEightZeroPercentSeniorNotesDueTwentyTwentyOneMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_NoncurrentLeaseLiabilitiesAbstract" abstract="true" name="NoncurrentLeaseLiabilitiesAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_PaymentsForProceedsFromMarketableSecurities" abstract="false" name="PaymentsForProceedsFromMarketableSecurities" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_ApolloConseiletCourtageMember" abstract="true" name="ApolloConseiletCourtageMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_EuropeMiddleEastAndAfricaMember" abstract="true" name="EuropeMiddleEastAndAfricaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_AnnuitiesMember" abstract="true" name="AnnuitiesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_SeniorNotes625PercentDue2040Member" abstract="true" name="SeniorNotes625PercentDue2040Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_FiduciaryAssetsPremiumTrustBalances" abstract="false" name="FiduciaryAssetsPremiumTrustBalances" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_DeferredTaxAssetsLeaseLiability" abstract="false" name="DeferredTaxAssetsLeaseLiability" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_ChangeInCapitalizedContractCostsRollForward" abstract="true" name="ChangeInCapitalizedContractCostsRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_DefinedBenefitPlanMaximumPercentageofMedicalSupplementPlanIntoFuturePeriods" abstract="false" name="DefinedBenefitPlanMaximumPercentageofMedicalSupplementPlanIntoFuturePeriods" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="num:percentItemType"/>
  <xs:element id="aon_DeferredTaxLiabilitiesOtherAccruedExpenses" abstract="false" name="DeferredTaxLiabilitiesOtherAccruedExpenses" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_ChangesInAccumulatedOtherComprehensiveIncomeLossRollForward" abstract="true" name="ChangesInAccumulatedOtherComprehensiveIncomeLossRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_EliminationsAndReconcilingItemsMember" abstract="true" name="EliminationsAndReconcilingItemsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_CreditFacilityExpiringFebruary2022Member" abstract="true" name="CreditFacilityExpiringFebruary2022Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_FinanceLeaseCost1Abstract" abstract="true" name="FinanceLeaseCost1Abstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_PilkingtonNorthAmericaInc.Member" abstract="true" name="PilkingtonNorthAmericaInc.Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_A2.20SeniorNotesdueNovember2020Member" abstract="true" name="A2.20SeniorNotesdueNovember2020Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_DistributableReservesAvailableAmount" abstract="false" name="DistributableReservesAvailableAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_AonHewittInvestmentConsultingIncMember" abstract="true" name="AonHewittInvestmentConsultingIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_TheNetherlandsAndCanadaMember" abstract="true" name="TheNetherlandsAndCanadaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_OtherCountryMember" abstract="true" name="OtherCountryMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_ScheduleofPerformanceBasedPlansTableTextBlock" abstract="false" name="ScheduleofPerformanceBasedPlansTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType"/>
  <xs:element id="aon_TreasuryStockAcquiredAdditionalTransactionCosts" abstract="false" name="TreasuryStockAcquiredAdditionalTransactionCosts" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_AlternativeInvestmentsMember" abstract="true" name="AlternativeInvestmentsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_TempoBusinessMember" abstract="true" name="TempoBusinessMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_IncreaseDecreaseInOperatingLeaseLiabilitiesNoncurrent" abstract="false" name="IncreaseDecreaseInOperatingLeaseLiabilitiesNoncurrent" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="aon_ShareRepurchaseProgramof2014Member" abstract="true" name="ShareRepurchaseProgramof2014Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="aon_IncomeLossFromContinuingOperationsBeforeIncomeTaxesAbstract" abstract="true" name="IncomeLossFromContinuingOperationsBeforeIncomeTaxesAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="aon_A3.875SeniorNotesdueDecember2025Member" abstract="true" name="A3.875SeniorNotesdueDecember2025Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
</xs:schema>
