Derivatives and Hedging Foreign Exchange Risk Management Narrative (Details)	9 Months Ended
Sep. 30, 2014
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Foreign currency exposures, maximum hedging period	1 year
Cash Flow Hedging [Member]
Derivative [Line Items]
Foreign currency exposures, maximum average hedging period	2 years
Foreign currency exposures, maximum hedging period	5 years
Net Investment Hedging [Member]
Derivative [Line Items]
Foreign currency exposures, maximum hedging period	2 years

Maximum average contract period for foreign currency exchange rate derivatives.

No definition available.

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

- Definition

Maximum length of time over which the entity is hedging its exposure to the variability in future exchange rates on its net investments in foreign operations.

+ References

No definition available.

+ Details

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

- Definition

Maximum length of time over which the entity is hedging its exposure to the variability in future exchange rates using instruments not designated as accounting hedges.

+ References

No definition available.

+ Details

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

- Details

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

- Definition

Maximum period of time the entity is hedging its exposure to variability in future cash flows for forecasted transactions, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Excludes forecasted transactions related to payment of variable interest on existing financial instruments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7668309&loc=d3e80748-113994

+ Details

Name:	us-gaap_MaximumLengthOfTimeForeignCurrencyCashFlowHedge
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration