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v2.4.1.9

Guarantee of Registered Securities - Condensed Consolidating Statement of Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2013 | Sep. 30, 2013 | Jun. 30, 2013 | Mar. 31, 2013 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net income | $ 467 us-gaap_ProfitLoss | $ 315 us-gaap_ProfitLoss | $ 313 us-gaap_ProfitLoss | $ 336 us-gaap_ProfitLoss | $ 360 us-gaap_ProfitLoss | $ 264 us-gaap_ProfitLoss | $ 252 us-gaap_ProfitLoss | $ 272 us-gaap_ProfitLoss | $ 1,431 us-gaap_ProfitLoss | $ 1,148 us-gaap_ProfitLoss | $ 1,020 us-gaap_ProfitLoss
Less: Net income attributable to noncontrolling interests | 8 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | 6 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | 9 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | 11 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | 5 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | 8 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | 11 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | 11 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | 34 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | 35 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | 27 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest
Net income attributable to Aon shareholders | 459 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 309 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 304 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 325 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 355 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 256 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 241 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 261 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 1,397 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 1,113 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 993 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
Change in fair value of investments |  |  |  |  |  |  |  |  | (1)us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax | 1 us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax | 0 us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax
Change in fair value of derivatives |  |  |  |  |  |  |  |  | 5 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax | 6 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax | 9 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax
Foreign currency translation adjustments |  |  |  |  |  |  |  |  | (507)us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax | (65)us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax | 109 us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax
Post-retirement benefit obligation |  |  |  |  |  |  |  |  | (260)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax | 293 us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax | (358)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax
Total other comprehensive loss |  |  |  |  |  |  |  |  | (763)us-gaap_OtherComprehensiveIncomeLossNetOfTax | 235 us-gaap_OtherComprehensiveIncomeLossNetOfTax | (240)us-gaap_OtherComprehensiveIncomeLossNetOfTax
Equity in other comprehensive loss of subsidiaries, net of tax |  |  |  |  |  |  |  |  | 0 aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries | 0 aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries | 0 aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries
Less: Other comprehensive (loss) income attributable to noncontrolling interests |  |  |  |  |  |  |  |  | (3)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest | (1)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest
Total other comprehensive (loss) income attributable to Aon shareholders |  |  |  |  |  |  |  |  | (760)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent | 236 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent | (240)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent
Comprehensive income attributable to Aon shareholders |  |  |  |  |  |  |  |  | 637 us-gaap_ComprehensiveIncomeNetOfTax | 1,349 us-gaap_ComprehensiveIncomeNetOfTax | 753 us-gaap_ComprehensiveIncomeNetOfTax
Aon plc [Member] |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net income |  |  |  |  |  |  |  |  | 1,397 us-gaap_ProfitLoss / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 1,113 us-gaap_ProfitLoss / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 993 us-gaap_ProfitLoss / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Less: Net income attributable to noncontrolling interests |  |  |  |  |  |  |  |  | 0 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Net income attributable to Aon shareholders |  |  |  |  |  |  |  |  | 1,397 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 1,113 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 993 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Change in fair value of investments |  |  |  |  |  |  |  |  | 0 us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |
Change in fair value of derivatives |  |  |  |  |  |  |  |  | 0 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Foreign currency translation adjustments |  |  |  |  |  |  |  |  | 0 us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Post-retirement benefit obligation |  |  |  |  |  |  |  |  | 0 us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Total other comprehensive loss |  |  |  |  |  |  |  |  | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Equity in other comprehensive loss of subsidiaries, net of tax |  |  |  |  |  |  |  |  | (760)aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 236 aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (240)aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Less: Other comprehensive (loss) income attributable to noncontrolling interests |  |  |  |  |  |  |  |  | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Total other comprehensive (loss) income attributable to Aon shareholders |  |  |  |  |  |  |  |  | (760)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 236 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | (240)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Comprehensive income attributable to Aon shareholders |  |  |  |  |  |  |  |  | 637 us-gaap_ComprehensiveIncomeNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 1,349 us-gaap_ComprehensiveIncomeNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 753 us-gaap_ComprehensiveIncomeNetOfTax / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Aon Corporation [Member] |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net income |  |  |  |  |  |  |  |  | 565 us-gaap_ProfitLoss / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 815 us-gaap_ProfitLoss / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 939 us-gaap_ProfitLoss / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember
Less: Net income attributable to noncontrolling interests |  |  |  |  |  |  |  |  | 0 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 0 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 0 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember
Net income attributable to Aon shareholders |  |  |  |  |  |  |  |  | 565 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 815 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 939 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember
Change in fair value of investments |  |  |  |  |  |  |  |  | 0 us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 0 us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember |
Change in fair value of derivatives |  |  |  |  |  |  |  |  | (3)us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 5 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 2 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember
Foreign currency translation adjustments |  |  |  |  |  |  |  |  | (31)us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | (60)us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 24 us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember
Post-retirement benefit obligation |  |  |  |  |  |  |  |  | (315)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 223 us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | (68)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember
Total other comprehensive loss |  |  |  |  |  |  |  |  | (349)us-gaap_OtherComprehensiveIncomeLossNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 168 us-gaap_OtherComprehensiveIncomeLossNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | (42)us-gaap_OtherComprehensiveIncomeLossNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember
Equity in other comprehensive loss of subsidiaries, net of tax |  |  |  |  |  |  |  |  | (411)aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 69 aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | (187)aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember
Less: Other comprehensive (loss) income attributable to noncontrolling interests |  |  |  |  |  |  |  |  | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember
Total other comprehensive (loss) income attributable to Aon shareholders |  |  |  |  |  |  |  |  | (760)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 237 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | (229)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember
Comprehensive income attributable to Aon shareholders |  |  |  |  |  |  |  |  | (195)us-gaap_ComprehensiveIncomeNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 1,052 us-gaap_ComprehensiveIncomeNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember | 710 us-gaap_ComprehensiveIncomeNetOfTax / dei_LegalEntityAxis = us-gaap_GuarantorSubsidiariesMember
Other Non-Guarantor Subsidiaries [Member] |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net income |  |  |  |  |  |  |  |  | 1,588 us-gaap_ProfitLoss / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 1,376 us-gaap_ProfitLoss / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 1,128 us-gaap_ProfitLoss / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember
Less: Net income attributable to noncontrolling interests |  |  |  |  |  |  |  |  | 34 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 35 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 27 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember
Net income attributable to Aon shareholders |  |  |  |  |  |  |  |  | 1,554 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 1,341 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 1,101 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember
Change in fair value of investments |  |  |  |  |  |  |  |  | (1)us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 1 us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember |
Change in fair value of derivatives |  |  |  |  |  |  |  |  | 8 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 1 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 7 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember
Foreign currency translation adjustments |  |  |  |  |  |  |  |  | (476)us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | (5)us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 85 us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember
Post-retirement benefit obligation |  |  |  |  |  |  |  |  | 55 us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 70 us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | (290)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember
Total other comprehensive loss |  |  |  |  |  |  |  |  | (414)us-gaap_OtherComprehensiveIncomeLossNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 67 us-gaap_OtherComprehensiveIncomeLossNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | (198)us-gaap_OtherComprehensiveIncomeLossNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember
Equity in other comprehensive loss of subsidiaries, net of tax |  |  |  |  |  |  |  |  | 0 aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 0 aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 0 aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember
Less: Other comprehensive (loss) income attributable to noncontrolling interests |  |  |  |  |  |  |  |  | (3)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | (1)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember
Total other comprehensive (loss) income attributable to Aon shareholders |  |  |  |  |  |  |  |  | (411)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 68 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | (198)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember
Comprehensive income attributable to Aon shareholders |  |  |  |  |  |  |  |  | 1,143 us-gaap_ComprehensiveIncomeNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 1,409 us-gaap_ComprehensiveIncomeNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember | 903 us-gaap_ComprehensiveIncomeNetOfTax / dei_LegalEntityAxis = us-gaap_NonGuarantorSubsidiariesMember
Consolidating Adjustments [Member] |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net income |  |  |  |  |  |  |  |  | (2,119)us-gaap_ProfitLoss / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | (2,156)us-gaap_ProfitLoss / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | (2,040)us-gaap_ProfitLoss / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember
Less: Net income attributable to noncontrolling interests |  |  |  |  |  |  |  |  | 0 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 0 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 0 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember
Net income attributable to Aon shareholders |  |  |  |  |  |  |  |  | (2,119)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | (2,156)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | (2,040)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember
Change in fair value of investments |  |  |  |  |  |  |  |  | 0 us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 0 us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember |
Change in fair value of derivatives |  |  |  |  |  |  |  |  | 0 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 0 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 0 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember
Foreign currency translation adjustments |  |  |  |  |  |  |  |  | 0 us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 0 us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 0 us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember
Post-retirement benefit obligation |  |  |  |  |  |  |  |  | 0 us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 0 us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 0 us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember
Total other comprehensive loss |  |  |  |  |  |  |  |  | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember
Equity in other comprehensive loss of subsidiaries, net of tax |  |  |  |  |  |  |  |  | 1,171 aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | (305)aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 427 aon_EquityOtherComprehensiveIncomeLossFromSubsidiaries / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember
Less: Other comprehensive (loss) income attributable to noncontrolling interests |  |  |  |  |  |  |  |  | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 0 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember
Total other comprehensive (loss) income attributable to Aon shareholders |  |  |  |  |  |  |  |  | 1,171 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | (305)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | 427 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember
Comprehensive income attributable to Aon shareholders |  |  |  |  |  |  |  |  | $ (948)us-gaap_ComprehensiveIncomeNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | $ (2,461)us-gaap_ComprehensiveIncomeNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember | $ (1,613)us-gaap_ComprehensiveIncomeNetOfTax / dei_LegalEntityAxis = us-gaap_ConsolidationEliminationsMember

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