Goodwill and Other Intangible Assets (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Goodwill and Intangible Assets
Tradenames	$ 1,019		$ 1,019
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	4,335		4,323
Intangible assets with finite lives, Accumulated Amortization	1,835		1,745
Intangible assets, Net Carrying Amount	2,500		2,578
Amortization expense on intangible assets	86	99
Estimated amortization for intangible assets
Remainder of 2014	260
2015	295
2016	247
2017	200
2018	140
Thereafter	339
Estimated future amortization for intangible assets	1,481
Risk Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2014	77
2015	83
2016	70
2017	59
2018	47
Thereafter	89
Estimated future amortization for intangible assets	425
HR Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2014	183
2015	212
2016	177
2017	141
2018	93
Thereafter	250
Estimated future amortization for intangible assets	1,056
Customer related and contract based [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	2,729		2,720
Intangible assets with finite lives, Accumulated Amortization	1,386		1,310
Intangible assets, Net Carrying Amount	1,343		1,410
Marketing, technology and other [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	587		584
Intangible assets with finite lives, Accumulated Amortization	449		435
Intangible assets, Net Carrying Amount	$ 138		$ 149