v2.3.0.15

Goodwill and Other Intangible Assets (Details) (USD $) In Millions | 9 Months Ended
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Sep. 30, 2011
Changes in the net carrying amount of goodwill by operating segment (in millions) |
Balance at the beginning of the period | $ 8,647
Goodwill related to current year acquisitions | 58
Goodwill related to disposals | (2)
Goodwill related to prior year acquisitions | 67
Foreign currency revaluation and other | 65
Balance at the end of the period | 8,835
Risk Solutions |
Changes in the net carrying amount of goodwill by operating segment (in millions) |
Balance at the beginning of the period | 5,549
Goodwill related to current year acquisitions | 54
Goodwill related to disposals | (2)
Transfers | (83)
Foreign currency revaluation and other | 11
Balance at the end of the period | 5,529
HR Solutions |
Changes in the net carrying amount of goodwill by operating segment (in millions) |
Balance at the beginning of the period | 3,098
Goodwill related to current year acquisitions | 4
Goodwill related to prior year acquisitions | 67
Transfers | 83
Foreign currency revaluation and other | 54
Balance at the end of the period | $ 3,306

X
- Definition Represents the transfers during the reporting period taken place in the carrying value of goodwill. + Details
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Namespace Prefix: | aon
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Net changes to the recorded value of goodwill for foreign currency translation adjustments. + Details
Name: | aon_GoodwillTranslationAdjustments
Namespace Prefix: | aon
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Carrying amount as of the balance sheet date, which is the cumulative amount paid, adjusted for any amortization recognized prior to adoption of FAS 142 and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 43 + Details
Name: | us-gaap_Goodwill
Namespace Prefix: | us-gaap
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The aggregate amount of goodwill acquired in the period and allocated to the reportable segment. The value is stated at fair value based on the purchase price allocation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph e(1) + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Purchase price allocation adjustment for allocation not yet complete at the prior year end. + Details
Name: | us-gaap_GoodwillAllocationAdjustment
Namespace Prefix: | us-gaap
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + Details
Name: | us-gaap_GoodwillRollForward
Namespace Prefix: | us-gaap
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Write-off of the carrying amount of goodwill associated with all or a portion of a reporting unit that is sold in the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph e(3) + Details
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Namespace Prefix: | us-gaap
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration