Acquisitions and Dispositions (Details 2) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2012 item	Jun. 30, 2011 item
Dispositions
Pretax gain (loss) recognized on sale of businesses	2
Risk Solutions
Dispositions
Number of dispositions	1
HR Solutions
Dispositions
Number of dispositions	1	1
Pretax gain (loss) recognized on sale of businesses		$ (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