Goodwill and Other Intangible Assets (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Intangible assets with indefinite lives
Trademarks	$ 1,024		$ 1,024		$ 1,024
Intangible assets with finite lives
Intangible assets with finite lives, gross carrying amount	4,310		4,310		4,242
Intangible assets with finite lives, accumulated amortization	1,270		1,270		966
Intangible assets, net	3,040		3,040		3,276
Amortization expense on intangible assets	105	91	313	273
Estimated amortization for intangible assets
Remainder of 2012			108
2013			390
2014			336
2015			292
2016			245
Thereafter			645
Estimated future amortization for intangible assets			2,016
HR Solutions
Estimated amortization for intangible assets
Remainder of 2012			76
2013			278
2014			240
2015			210
2016			175
Thereafter			478
Estimated future amortization for intangible assets			1,457
Risk Solutions
Estimated amortization for intangible assets
Remainder of 2012			32
2013			112
2014			96
2015			82
2016			70
Thereafter			167
Estimated future amortization for intangible assets			559
Trademarks
Intangible assets with finite lives
Intangible assets with finite lives, gross carrying amount	6		6		4
Intangible assets with finite lives, accumulated amortization	2		2		1
Intangible assets, net	4		4		3
Customer related and contract based
Intangible assets with finite lives
Intangible assets with finite lives, gross carrying amount	2,671		2,671		2,608
Intangible assets with finite lives, accumulated amortization	874		874		615
Intangible assets, net	1,797		1,797		1,993
Marketing, technology and other
Intangible assets with finite lives
Intangible assets with finite lives, gross carrying amount	609		609		606
Intangible assets with finite lives, accumulated amortization	394		394		350
Intangible assets, net	$ 215		$ 215		$ 256