Acquisitions and Dispositions Dispositions (Details) (Disposal Groups [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Dispositions
Pretax gain recognized on sale of businesses	$ 10	$ 1	$ 0
Risk Solutions [Member]
Dispositions
Number of dispositions	7	3	2
HR Solutions [Member]
Dispositions
Number of dispositions	2	1

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