This element represents the amount of coverage as contended by the insurers for the loss.

Name:	aon_LossContingencyCoverageFromInsurers
Namespace Prefix:	aon
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents the difference amount of damages sought by the client after adjusting for amount claimed from insurers.

+ Details

Name:	aon_LossContingencyDamagesDifferenceAmountSoughtValue
Namespace Prefix:	aon
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The value (monetary amount) of the award the plaintiff seeks in the legal matter.

+ Details

Name:	aon_LossContingencyDamagesSoughtValue
Namespace Prefix:	aon
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The estimated maximum amount of possible loss with respect to contractual contingent guarantees for premium payments owed by clients to certain insurance companies.

+ Details

Name:	aon_LossContractualContingentGuaranteesRangeOfPossibleLossMaximum
Namespace Prefix:	aon
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Payments made to fund limited partnership interest and reduce related guaranteed commitment.

+ Details

Name:	aon_PartnershipObligationsFunded
Namespace Prefix:	aon
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the agreed amount which entity would pay in exchange for dismissal of class claims.

+ Details

Name:	aon_PaymentOnDismissalOfClassClaims
Namespace Prefix:	aon
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Settlement agreement to pay fine arising from failure to exercise reasonable care to establish and maintain effective systems and controls to counter the risks of bribery arising from the use of overseas firms and individuals who helped win business.

+ Details

Name:	aon_SettlementAgreementToPayFine
Namespace Prefix:	aon
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

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

-Publisher FASB

-Name FASB Interpretation (FIN)

-Number 45

-Paragraph 13

-Subparagraph b

+ Details

Name:	us-gaap_GuaranteeObligationsMaximumExposure
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ Details

Name:	us-gaap_LossContingenciesLineItems
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Commitments and Contingencies (Details)	1 Months Ended			1 Months Ended	3 Months Ended	9 Months Ended
Commitments and Contingencies (Details)	Mar. 31, 2011 USD ($)	Jan. 31, 2009 GBP (£)	Sep. 30, 2011 USD ($)	May 31, 2010 Opry Mills Mall Limited Partnership USD ($)	Sep. 30, 2011 Commitments to fund certain limited partnerships USD ($)	Sep. 30, 2011 Commitments to fund certain limited partnerships USD ($)
Legal, Guarantees and Indemnifications
Agreed upon payment in exchange for dismissal of class claims	$ 550,000
Settlement agreement with the FSA to pay fine (amount in GBP)		5,250,000
Damages sought by Opry Mills Mall Limited Partnership				200,000,000
Amount of coverage for damages contended by the insurers				50,000,000
Difference amount of damages sought by the client				150,000,000
Estimated exposure with respect to contractual contingent guarantees for premium payments owed by clients			8,000,000
Maximum potential funding under commitments					69,000,000	69,000,000
Commitments funded					$ 1,000,000	$ 13,000,000