Goodwill and Other Intangible Assets (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013		Jun. 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	4,284			4,284			4,358
Intangible assets with finite lives, Accumulated Amortization	1,548			1,548			1,383
Intangible assets, Net Carrying Amount	2,736			2,736			2,975
Amortization expense on intangible assets	99		104	198		208
Estimated amortization for intangible assets
Remainder of 2013	194			194
2014	334			334
2015	288			288
2016	242			242
2017	196			196
Thereafter	457			457
Estimated future amortization for intangible assets	1,711			1,711
HR Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2013	139			139
2014	240			240
2015	209			209
2016	175			175
2017	139			139
Thereafter	338			338
Estimated future amortization for intangible assets	1,240			1,240
Risk Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2013	55			55
2014	94			94
2015	79			79
2016	67			67
2017	57			57
Thereafter	119			119
Estimated future amortization for intangible assets	471			471
Customer related and contract based [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	2,659			2,659			2,714
Intangible assets with finite lives, Accumulated Amortization	1,124			1,124			969
Intangible assets, Net Carrying Amount	1,535			1,535			1,745
Marketing, technology and other [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	600	[1]		600	[1]		619	[1]
Intangible assets with finite lives, Accumulated Amortization	424	[1]		424	[1]		414	[1]
Intangible assets, Net Carrying Amount	$ 176	[1]		$ 176	[1]		$ 205	[1]

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