Goodwill and Other Intangible Assets (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Dec. 31, 2012
Goodwill and Intangible Assets
Tradenames	$ 1,025			$ 1,025
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	4,300			4,358
Intangible assets with finite lives, Accumulated Amortization	1,456			1,383
Intangible assets, Net Carrying Amount	2,844			2,975
Amortization expense on intangible assets	99		104
Estimated amortization for intangible assets
Remainder of 2013	293
2014	339
2015	294
2016	246
2017	193
Thereafter	454
Estimated future amortization for intangible assets	1,819
HR Solutions
Estimated amortization for intangible assets
Remainder of 2013	208
2014	243
2015	212
2016	177
2017	140
Thereafter	347
Estimated future amortization for intangible assets	1,327
Risk Solutions
Estimated amortization for intangible assets
Remainder of 2013	85
2014	96
2015	82
2016	69
2017	53
Thereafter	107
Estimated future amortization for intangible assets	492
Customer related and contract based
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	2,670			2,714
Intangible assets with finite lives, Accumulated Amortization	1,037			969
Intangible assets, Net Carrying Amount	1,633			1,745
Marketing, technology and other (1)
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	605	[1]		619	[1]
Intangible assets with finite lives, Accumulated Amortization	419	[1]		414	[1]
Intangible assets, Net Carrying Amount	$ 186	[1]		$ 205	[1]

[1] Tradenames with finite lives disclosed separately in prior years are now presented in Marketing, technology and other