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

No definition available.

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

- Definition

Loss Contingency Damages Awarded Value Excluding Interest and Costs

+ References

No definition available.

+ Details

Name:	aon_LossContingencyDamagesAwardedValueExcludingInterestandCosts
Namespace Prefix:	aon_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

Loss Contingency, Settlement Agreement, Terms, Maximum Liability

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

Name:	aon_PartnershipObligationsFunded
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 Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

+ Details

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

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of judgment or settlement awarded to (against) the entity in respect of litigation.

+ References

No definition available.

+ Details

Name:	us-gaap_LitigationSettlementAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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.

+ References

No definition available.

+ Details

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

- Definition

Amount of damages awarded to the plaintiff in the legal matter.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 9

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

+ Details

Name:	us-gaap_LossContingencyDamagesAwardedValue
Namespace Prefix:	us-gaap_
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.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 9

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

+ Details

Name:	us-gaap_LossContingencyDamagesSoughtValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 9

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

+ Details

Name:	us-gaap_LossContingencyEstimateOfPossibleLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The estimated maximum amount of possible loss from the contingency.

+ References

+ Details

Name:	us-gaap_LossContingencyRangeOfPossibleLossMaximum
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The estimated minimum amount of possible loss from the contingency.

+ References

+ Details

Name:	us-gaap_LossContingencyRangeOfPossibleLossMinimum
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of cash paid for the settlement of litigation or for other legal issues during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3536-108585

+ Details

Name:	us-gaap_PaymentsForLegalSettlements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=aon_PotentialClaimforPensionAdvisoryServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_FinancialGuaranteeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationCaseAxis=aon_OpryMillsMallLimitedPartnershipMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationCaseAxis=aon_PhilipsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationCaseAxis=aon_InternationalRoadTransportUnionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=aon_LitigationForeignCurrencyDenominatedAwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=aon_LitigationUSDDenominatedAwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=aon_LitigationExpensesandInterestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationCaseAxis=aon_HuntingtonIngallsIndustriesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationCaseAxis=aon_VersicherungAktiengesellschaftMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationStatusAxis=us-gaap_PendingLitigationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationCaseAxis=aon_LyttletonPortCompanyLimitedMember
Namespace Prefix:
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Commitments and Contingencies (Details) € in Millions, £ in Millions, SFr in Millions, NZD in Millions											1 Months Ended						3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2015 USD ($)	Jun. 29, 2015 NZD	Jan. 26, 2015 USD ($)	Jan. 26, 2015 CHF (SFr)	Dec. 02, 2014 USD ($)	Dec. 02, 2014 CHF (SFr)	Jan. 02, 2014 GBP (£)	Sep. 14, 2010 USD ($)	Jun. 01, 2007 USD ($)	Jun. 01, 2007 CHF (SFr)	Aug. 31, 2015 USD ($)	Jun. 30, 2015 GBP (£)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2014 CHF (SFr)	Jun. 30, 2015 USD ($)	Jun. 30, 2015 EUR (€)	Jun. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)	Apr. 30, 2014 GBP (£)
Legal, Guarantees and Indemnifications
Range of possible loss, minimum	$ 0																			$ 0
Range of possible loss, maximum	300,000,000																			300,000,000
Letters of credit outstanding	59,000,000														$ 95,000,000					59,000,000
Maximum potential funding under commitments	82,000,000														112,000,000					82,000,000
Potential Claim for Pension Advisory Services [Member]
Legal, Guarantees and Indemnifications
Estimate of possible loss	68,000,000																			68,000,000	£ 45
Commitments to fund certain limited partnerships or subsidiaries [Member]
Legal, Guarantees and Indemnifications
Maximum potential funding under commitments	12,000,000														14,000,000					12,000,000
Commitments funded																				$ 2,000,000
Opry Mills Mall Limited Partnership [Member]
Legal, Guarantees and Indemnifications
Damages sought								$ 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
Damages awarded											$ 204,000,000			$ 200,000,000
Philips [Member]
Legal, Guarantees and Indemnifications
Damages sought	287,000,000						£ 189					£ 290	$ 440,000,000
International Road Transport Union [Member] \| Litigation Award [Member]
Legal, Guarantees and Indemnifications
Damages sought									$ 47,000,000	SFr 46.0
Damages awarded															28,000,000	SFr 27.9
Damages awarded excluding interest and costs	17,000,000					SFr 16.8
Case settlement amount			$ 13,000,000	SFr 12.8
Settlement, maximum liability			9,000,000	SFr 8.7
International Road Transport Union [Member] \| Litigation USD Denominated Award [Member]
Legal, Guarantees and Indemnifications
Damages sought									3,000,000
Damages awarded															$ 5,000,000
Damages awarded excluding interest and costs					$ 3,100,000
Case settlement amount			4,700,000
Settlement, maximum liability			$ 115,000
International Road Transport Union [Member] \| Litigation Expenses and Interest [Member]
Legal, Guarantees and Indemnifications
Damages sought									$ 30,000,000
Huntington Ingalls Industries [Member]
Legal, Guarantees and Indemnifications
Settlement payment																	$ 150,000,000
Versicherung Aktiengesellschaft [Member] \| Litigation Award [Member]
Legal, Guarantees and Indemnifications
Case settlement amount																		€ 1.6	$ 2,000,000
Pending Litigation [Member] \| Lyttleton Port Company Limited [Member]
Legal, Guarantees and Indemnifications
Damages sought	$ 117,500,000	NZD 184