Goodwill and Other Intangible Assets (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Intangible assets with indefinite lives
Trademarks	$ 1,025	$ 1,024
Intangible assets with finite lives
Intangible assets with finite lives, gross carrying amount	4,358	4,242
Intangible assets with finite lives, accumulated amortization	1,383	966
Intangible assets, net	2,975	3,276
Amortization expense on intangible assets	423	362	154
Estimated amortization for intangible assets
2013	394
2014	343
2015	299
2016	251
2017	199
Thereafter	464
Estimated future amortization for intangible assets	1,950
HR Solutions
Estimated amortization for intangible assets
2013	281
2014	245
2015	214
2016	179
2017	142
Thereafter	351
Estimated future amortization for intangible assets	1,412
Risk Solutions
Estimated amortization for intangible assets
2013	113
2014	98
2015	85
2016	72
2017	57
Thereafter	113
Estimated future amortization for intangible assets	538
Tradenames
Intangible assets with finite lives
Intangible assets with finite lives, gross carrying amount	7	4
Intangible assets with finite lives, accumulated amortization	3	1
Intangible assets, net	4	3
Customer related and contract based
Intangible assets with finite lives
Intangible assets with finite lives, gross carrying amount	2,714	2,608
Intangible assets with finite lives, accumulated amortization	969	615
Intangible assets, net	1,745	1,993
Marketing, technology and other
Intangible assets with finite lives
Intangible assets with finite lives, gross carrying amount	612	606
Intangible assets with finite lives, accumulated amortization	411	350
Intangible assets, net	$ 201	$ 256