Derivatives and Hedging - Foreign Exchange Risk Management Narrative (Details)	12 Months Ended
Dec. 31, 2014
Cash Flow Hedging [Member]
Derivative [Line Items]
Foreign currency exposures, maximum average hedging period	2 years
Net Investment Hedging [Member]
Derivative [Line Items]
Foreign currency exposures, maximum hedging period	2 years
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Maximum length of time hedged in foreign currency undesignated hedge	1 year

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.

No definition available.

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