Acquisitions and Dispositions Acquisitions (Details) (USD $) In Millions, unless otherwise specified										12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Risk Solutions [Member]	Dec. 31, 2012 Risk Solutions [Member]	Dec. 31, 2011 Risk Solutions [Member]	Dec. 31, 2013 HR Solutions [Member]	Dec. 31, 2012 HR Solutions [Member]	Dec. 31, 2011 HR Solutions [Member]	Dec. 31, 2013 Business Acquisitions [Member]	Dec. 31, 2012 Business Acquisitions [Member]	Dec. 31, 2013 Business Acquisitions [Member] Risk Solutions [Member] business	Dec. 31, 2012 Business Acquisitions [Member] Risk Solutions [Member] business	Dec. 31, 2013 Business Acquisitions [Member] HR Solutions [Member] business	Dec. 31, 2012 Business Acquisitions [Member] HR Solutions [Member] business
Business Acquisition
Number of business acquired under business combination												8	6	3	5
Consideration										$ 54	$ 175
Goodwill	8,997	8,943	8,770	6,020	5,982	5,557	2,977	2,961	3,213	38	90
Other intangible assets										28	100
Total										$ 66	$ 190