Acquisitions and Dispositions (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2011 item	Dec. 31, 2010 item
Dispositions
Number of dispositions			8
Pretax gain (loss) recognized on sale of businesses	1		(4)
Risk Solutions
Dispositions
Number of dispositions	3	2	7
HR Solutions
Dispositions
Number of dispositions	1		1