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v2.4.1.9

Share-Based Compensation Plans Performance Share Awards Narrative (Details) (Performance Shares [Member]) | 3 Months Ended
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Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Vesting conditions period | 3 years
Minimum [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Shares issued, percent | 0.00%aon_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedPercent / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Maximum [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Shares issued, percent | 200.00%aon_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedPercent / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_RangeAxis = us-gaap_MaximumMember

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- Definition Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued, Percent + References No definition available. + Details
Name: | aon_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedPercent
Namespace Prefix: | aon_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Share-based Compensation Arrangement by Share-based Payment Award, Vesting Conditions Period + References No definition available. + Details
Name: | aon_SharebasedCompensationArrangementbySharebasedPaymentAwardVestingConditionsPeriod
Namespace Prefix: | aon_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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