Acquisitions and Dispositions (Details 2) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012 item	Sep. 30, 2011 item
Dispositions
Pretax gain (loss) recognized on sale of businesses	1
Risk Solutions
Dispositions
Number of dispositions	2	2
Pretax gain (loss) recognized on sale of businesses		$ (2)
HR Solutions
Dispositions
Number of dispositions	1