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v2.4.1.9

Segment Information - Schedule of fiduciary investment income by business segment (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
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fiduciary investment income | $ 7 aon_FiduciaryInvestmentIncome | $ 7 aon_FiduciaryInvestmentIncome | $ 6 aon_FiduciaryInvestmentIncome | $ 6 aon_FiduciaryInvestmentIncome | $ 7 aon_FiduciaryInvestmentIncome | $ 8 aon_FiduciaryInvestmentIncome | $ 6 aon_FiduciaryInvestmentIncome | $ 7 aon_FiduciaryInvestmentIncome | $ 26 aon_FiduciaryInvestmentIncome | $ 28 aon_FiduciaryInvestmentIncome | $ 38 aon_FiduciaryInvestmentIncome
Risk Solutions [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fiduciary investment income |  |  |  |  |  |  |  |  | 26 aon_FiduciaryInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = aon_RiskAndInsuranceBrokerageServicesMember | 28 aon_FiduciaryInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = aon_RiskAndInsuranceBrokerageServicesMember | 38 aon_FiduciaryInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = aon_RiskAndInsuranceBrokerageServicesMember
HR Solutions [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fiduciary investment income |  |  |  |  |  |  |  |  | $ 0 aon_FiduciaryInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = aon_ConsultingMember | $ 0 aon_FiduciaryInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = aon_ConsultingMember | $ 0 aon_FiduciaryInvestmentIncome / us-gaap_StatementBusinessSegmentsAxis = aon_ConsultingMember

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- Definition Income earned on the interest-bearing assets used as temporary investments of premiums collected from insured's but not yet remitted to insurance companies. + References No definition available. + Details
Name: | aon_FiduciaryInvestmentIncome
Namespace Prefix: | aon_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
Name: | us-gaap_SegmentReportingInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=aon_ConsultingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=aon_RiskAndInsuranceBrokerageServicesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |