Goodwill and Other Intangible Assets (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Intangible assets with indefinite lives
Tradenames	$ 1,019		$ 1,019		$ 1,019
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	4,579		4,579		4,323
Intangible assets with finite lives, Accumulated Amortization	1,967		1,967		1,745
Intangible assets, Net Carrying Amount	2,612		2,612		2,578
Amortization expense on intangible assets	90	98	263	296
Estimated amortization for intangible assets
Remainder of 2014	89		89
2015	320		320
2016	276		276
2017	231		231
2018	172		172
Thereafter	505		505
Estimated future amortization for intangible assets	1,593		1,593
Risk Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2014	29		29
2015	109		109
2016	100		100
2017	91		91
2018	79		79
Thereafter	253		253
Estimated future amortization for intangible assets	661		661
HR Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2014	60		60
2015	211		211
2016	176		176
2017	140		140
2018	93		93
Thereafter	252		252
Estimated future amortization for intangible assets	932		932
Customer related and contract based [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	2,972		2,972		2,720
Intangible assets with finite lives, Accumulated Amortization	1,520		1,520		1,310
Intangible assets, Net Carrying Amount	1,452		1,452		1,410
Marketing, technology and other [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	588		588		584
Intangible assets with finite lives, Accumulated Amortization	447		447		435
Intangible assets, Net Carrying Amount	$ 141		$ 141		$ 149