Acquisitions and Dispositions - Dispositions (Details) (Risk Solutions [Member], USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2014 business	Sep. 30, 2013 business	Sep. 30, 2014 business	Sep. 30, 2013 business
Risk Solutions [Member]
Dispositions
Number of dispositions	1	1	2	5
Gain (loss) recognized on sale	$ 25.0	$ 0.2	$ 25.0	$ 0.2

The gain (loss) resulting from the sale of a disposal group that is not a discontinued operation and other income. It is included in income from continuing operations before income taxes in the income statement.

No definition available.

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