Goodwill and Other Intangible Assets (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Intangible assets with indefinite lives
Trademarks	$ 1,024		$ 1,024
Intangible assets with finite lives
Intangible assets with finite lives, accumulated amortization	1,081		966
Intangible assets with finite lives, gross carrying amount	4,284		4,242
Intangible assets, net	3,203		3,276
Amortization expense on intangible assets	104	91
Estimated amortization for intangible assets
Remainder of 2012	313
2013	377
2014	330
2015	285
2016	241
Thereafter	633
Estimated future amortization for intangible assets	2,179
HR Solutions
Estimated amortization for intangible assets
Remainder of 2012	223
2013	276
2014	239
2015	209
2016	175
Thereafter	478
Estimated future amortization for intangible assets	1,600
Risk Solutions
Estimated amortization for intangible assets
Remainder of 2012	90
2013	101
2014	91
2015	76
2016	66
Thereafter	155
Estimated future amortization for intangible assets	579
Trademarks
Intangible assets with finite lives
Intangible assets with finite lives, accumulated amortization	1		1
Intangible assets with finite lives, gross carrying amount	4		4
Intangible assets, net	3		3
Customer Related and Contract Based
Intangible assets with finite lives
Intangible assets with finite lives, accumulated amortization	711		615
Intangible assets with finite lives, gross carrying amount	2,642		2,608
Intangible assets, net	1,931		1,993
Marketing, Technology and Other
Intangible assets with finite lives
Intangible assets with finite lives, accumulated amortization	369		350
Intangible assets with finite lives, gross carrying amount	614		606
Intangible assets, net	$ 245		$ 256