Name:	aon_AmountOfEquityInvestmentsExchangedForDebentures
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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

The value of debentures cancelled in a trust dissolution exchange transaction.

No definition available.

Name:	aon_DebenturesCancelledAmount
Namespace Prefix:	aon_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Reflects as of the balance sheet date the actual annualized interest rate that includes both LIBOR and the contractual variable rate margin.

No definition available.

Name:	aon_DebtAnnualizedInterestRate
Namespace Prefix:	aon_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

This element represents the carrying value of debt instrument related to hedging activities.

No definition available.

Name:	aon_DebtInstrumentCarryingAmountRelatedToHedgingActivities
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents the upper limit of non-recurring cash charges permitted by the entity's debt covenants related to an acquisition.

No definition available.

Name:	aon_DebtInstrumentCovenantAcquisitionTransactionCostLimit
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Represents the ratio of consolidated EBITDA (earnings before interest, taxes, depreciation and amortization) less transaction costs to consolidated interest expense ratio required to be maintained under financial covenants.

No definition available.

Name:	aon_DebtInstrumentCovenantRatioConsolidatedEBITDALessTransactionCostsToConsolidatedCashInterestExpense
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Data Type:	xbrli:pureItemType
Balance Type:	na
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Represents the maximum ratio of consolidated indebtedness to consolidated EBITDA (earnings before interest, taxes, depreciation and amortization) ratio permitted under financial covenants.

No definition available.

Name:	aon_DebtInstrumentMaximumCovenantRatioConsolidatedIndebtednessToConsolidatedEBITDA
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Data Type:	xbrli:pureItemType
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Represents the gain realized from the repurchase of trust capital securities, which was reported in other income (expense) in the consolidated statement of income.

No definition available.

Name:	aon_GainOnRepurchaseOfTrustCapitalSecurities
Namespace Prefix:	aon_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Line of Credit Facility, Term

No definition available.

Name:	aon_LineOfCreditFacilityTerm
Namespace Prefix:	aon_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the percentage of common equity in a trust.

No definition available.

Name:	aon_PercentageOfCommonEquityInTrust
Namespace Prefix:	aon_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the face value of repurchased preferred capital securities issued by a business trust or other special purpose entity.

No definition available.

Name:	aon_PreferredStockParOrStatedValueRepurchased
Namespace Prefix:	aon_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Reflects the calculation as of the balance sheet date of the average interest rate weighted by the average outstanding amount of short-term debt outstanding by type or by instrument at that time.

No definition available.

Name:	aon_ShortTermDebtAverageOutstandingAmountWeightedAverageInterestRate
Namespace Prefix:	aon_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

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-Subparagraph (SX 210.7-03.16)

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-Subparagraph (SX 210.9-03.13,16)

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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-Article 5

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The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

No definition available.

Name:	us-gaap_DebtInstrumentDescriptionOfVariableRateBasis
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Data Type:	xbrli:stringItemType
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Period Type:	duration

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

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Name:	us-gaap_DebtInstrumentFaceAmount
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Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

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-Number 210

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- Details

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The amount of debt premium that was originally recognized at the issuance of the instrument that has yet to be amortized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Topic 835

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Name:	us-gaap_DebtInstrumentUnamortizedPremium
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For an unclassified balance sheet, the amount as of the balance sheet date of capitalized costs associated with the issuance of debt instruments (for example, legal, accounting, underwriting, printing, and registration costs) that will be charged against earnings over the life of the debt instruments to which such costs pertain. Such amount is before the consideration of accumulated amortization.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Topic 230

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The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

No definition available.

Name:	us-gaap_LineOfCreditFacilityCommitmentFeePercentage
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Data Type:	num:percentItemType
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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

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-Subparagraph (SX 210.5-02.19(b),22(b))

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The cash outflow to reacquire preferred stocks issued by a business trust or other special purpose entity, mainly established by a bank holding entity, to third party investors. The trust's assets are deeply subordinated debentures of the bank holding entity. Most trust preferred securities are subject to a mandatory redemption upon the repayment of the debentures.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Topic 230

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Name:	us-gaap_PaymentsForRepurchaseOfTrustPreferredSecurities
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Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

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-Section S99

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-Subparagraph (SX 210.4-08.(f))

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-Number 210

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-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

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-Topic 230

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Name:	us-gaap_ProceedsFromLinesOfCredit
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Data Type:	xbrli:monetaryItemType
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The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

No definition available.

Name:	us-gaap_RepaymentsOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period.

No definition available.

Name:	us-gaap_ShorttermDebtAverageOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Write-off of amounts previously capitalized as debt issuance cost in an extinguishment of debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.8)

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