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

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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

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

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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

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+ Details

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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

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-SubTopic 20
-Section 50
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-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

+ Details

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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
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+ Details

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

- Definition

Cash outflow related to the acquisition or continued holding of limited partnership interests held for investment purposes.

+ References

No definition available.

+ Details

Name:	us-gaap_PaymentsToAcquireLimitedPartnershipInterests
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

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- Details

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Namespace Prefix:
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Balance Type:
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- Details

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Namespace Prefix:
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- Details

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Commitments and Contingencies (Details) £ in Millions, NZD in Millions											1 Months Ended					3 Months Ended	9 Months Ended
	Sep. 30, 2016 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 (£)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2014 CHF (SFr)	Sep. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	Apr. 30, 2014 GBP (£)
Legal, Guarantees and Indemnifications
Letters of credit outstanding	$ 91,000,000															$ 91,000,000	$ 91,000,000		$ 58,000,000
Maximum potential funding under commitments	82,000,000															82,000,000	82,000,000		104,000,000
Payments to funds																(2,000,000)	(2,000,000)
Potential Claim for Pension Advisory Services [Member]
Legal, Guarantees and Indemnifications
Estimate of possible loss	58,000,000															58,000,000	58,000,000			£ 45
Commitments to fund certain limited partnerships or subsidiaries [Member]
Legal, Guarantees and Indemnifications
Maximum potential funding under commitments	10,000,000															10,000,000	10,000,000	$ 12,000,000	$ 12,000,000
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	376,000,000						£ 189					£ 290					245,000,000
International Road Transport Union [Member] \| Litigation Award [Member]
Legal, Guarantees and Indemnifications
Damages sought	47,000,000									SFr 46,000,000
Damages awarded	29,000,000														SFr 27,900,000
Damages awarded excluding interest and costs	17,000,000					SFr 16,800,000
Case settlement amount	14,000,000			SFr 12,800,000
Settlement, maximum liability	9,000,000			SFr 8,700,000.0
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
Pending Litigation [Member] \| Lyttleton Port Company Limited [Member]
Legal, Guarantees and Indemnifications
Damages sought	134,000,000	NZD 184
Minimum [Member]
Legal, Guarantees and Indemnifications
Estimate of possible loss	0															0	0
Maximum [Member]
Legal, Guarantees and Indemnifications
Estimate of possible loss	$ 200,000,000															$ 200,000,000	$ 200,000,000