Segment Information Schedule of reconciliation of segment income before tax to income from continuing operations before income taxes (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]
Operating income from continuing operations before income taxes	$ 515	$ 364	$ 382	$ 410	$ 461	$ 339	$ 394	$ 402	$ 1,671	$ 1,596	$ 1,596
Interest income									9	10	18
Interest expense									(210)	(228)	(245)
Other income									68	2	19
Income before income taxes									1,538	1,380	1,388
Risk Solutions [Member]
Segment Reporting Information [Line Items]
Operating income from continuing operations before income taxes									1,540	1,493	1,413
HR Solutions [Member]
Segment Reporting Information [Line Items]
Operating income from continuing operations before income taxes									318	289	336
Total operating segments [Member]
Segment Reporting Information [Line Items]
Operating income from continuing operations before income taxes									1,858	1,782	1,749
Unallocated expense [Member]
Segment Reporting Information [Line Items]
Operating income from continuing operations before income taxes									$ (187)	$ (186)	$ (153)