Goodwill and Other Intangible Assets (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012	Dec. 31, 2012
Goodwill and Intangible Assets
Tradenames	$ 1,025			$ 1,025			$ 1,025
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	4,322			4,322			4,358
Intangible assets with finite lives, Accumulated Amortization	1,665			1,665			1,383
Intangible assets, Net Carrying Amount	2,657			2,657			2,975
Amortization expense on intangible assets	98		105	296		313
Estimated amortization for intangible assets
Remainder of 2013	98			98
2014	338			338
2015	291			291
2016	244			244
2017	196			196
Thereafter	465			465
Estimated future amortization for intangible assets	1,632			1,632
HR Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2013	70			70
2014	243			243
2015	212			212
2016	177			177
2017	140			140
Thereafter	342			342
Estimated future amortization for intangible assets	1,184			1,184
Risk Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2013	28			28
2014	95			95
2015	79			79
2016	67			67
2017	56			56
Thereafter	123			123
Estimated future amortization for intangible assets	448			448
Customer related and contract based [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	2,686			2,686			2,714
Intangible assets with finite lives, Accumulated Amortization	1,218			1,218			969
Intangible assets, Net Carrying Amount	1,468			1,468			1,745
Marketing, technology and other [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	611	[1]		611	[1]		619	[1]
Intangible assets with finite lives, Accumulated Amortization	447	[1]		447	[1]		414	[1]
Intangible assets, Net Carrying Amount	$ 164	[1]		$ 164	[1]		$ 205	[1]

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