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Acquisitions and Dispositions - Acquisitions (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended |
--- | --- | ---
Mar. 31, 2015 business | Mar. 31, 2014 business | Dec. 31, 2014
Intangible assets: |  |  |
Goodwill | $ 8,548 us-gaap_Goodwill |  | $ 8,860 us-gaap_Goodwill
Business Acquisition 1 [Member] |  |  |
Business Acquisition |  |  |
Consideration | 21 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = aon_BusinessAcquisition1Member | 5 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = aon_BusinessAcquisition1Member |
Intangible assets: |  |  |
Goodwill | 16 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = aon_BusinessAcquisition1Member | 4 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = aon_BusinessAcquisition1Member |
Other intangible assets | 1 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill / us-gaap_BusinessAcquisitionAxis = aon_BusinessAcquisition1Member | 4 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill / us-gaap_BusinessAcquisitionAxis = aon_BusinessAcquisition1Member |
Total | 17 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = aon_BusinessAcquisition1Member | 8 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = aon_BusinessAcquisition1Member |
Risk Solutions [Member] |  |  |
Business Acquisition |  |  |
Number of business acquired under business combination | 1 us-gaap_NumberOfBusinessesAcquired / us-gaap_StatementBusinessSegmentsAxis = aon_RiskAndInsuranceBrokerageServicesMember | 1 us-gaap_NumberOfBusinessesAcquired / us-gaap_StatementBusinessSegmentsAxis = aon_RiskAndInsuranceBrokerageServicesMember |
Intangible assets: |  |  |
Goodwill | 5,628 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = aon_RiskAndInsuranceBrokerageServicesMember |  | 5,911 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = aon_RiskAndInsuranceBrokerageServicesMember
HR Solutions [Member] |  |  |
Business Acquisition |  |  |
Number of business acquired under business combination | 1 us-gaap_NumberOfBusinessesAcquired / us-gaap_StatementBusinessSegmentsAxis = aon_ConsultingMember | 1 us-gaap_NumberOfBusinessesAcquired / us-gaap_StatementBusinessSegmentsAxis = aon_ConsultingMember |
Intangible assets: |  |  |
Goodwill | $ 2,920 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = aon_ConsultingMember |  | $ 2,949 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = aon_ConsultingMember

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- Definition Amount of intangible assets, excluding goodwill, acquired at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=56956791&loc=d3e4845-128472 + Details
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- Definition Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=56956791&loc=d3e4845-128472 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 55 -Paragraph 37 -URI http://asc.fasb.org/extlink&oid=35744172&loc=d3e2207-128464 + Details
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- Definition Amount of assets expected to be realized or consumed after one year or the normal operating cycle, if longer, acquired at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=56956791&loc=d3e4845-128472 + Details
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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266 + Details
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- Definition The number of businesses acquired by the entity during the period. + References No definition available. + Details
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