Segment Information Schedule of total revenue by business segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Revenue	$ 3,209	$ 2,794	$ 2,897	$ 2,915	$ 3,115	$ 2,737	$ 2,821	$ 2,841	$ 11,815	$ 11,514	$ 11,287
Total operating segments [Member]
Segment Reporting Information [Line Items]
Revenue									11,815	11,514	11,287
Risk Solutions [Member]
Segment Reporting Information [Line Items]
Revenue									7,789	7,632	7,537
HR Solutions [Member]
Segment Reporting Information [Line Items]
Revenue									4,057	3,925	3,781
Intersegment elimination [Member]
Segment Reporting Information [Line Items]
Revenue									$ (31)	$ (43)	$ (31)