Goodwill and Other Intangible Assets (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Goodwill and Intangible Assets
Tradenames	$ 1,019		$ 1,019		$ 1,019
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	4,400		4,400		4,323
Intangible assets with finite lives, Accumulated Amortization	1,932		1,932		1,745
Intangible assets, Net Carrying Amount	2,468		2,468		2,578
Amortization expense on intangible assets	87	99	173	198
Estimated amortization for intangible assets
Remainder of 2014	178		178
2015	307		307
2016	255		255
2017	205		205
2018	147		147
Thereafter	357		357
Estimated future amortization for intangible assets	1,449		1,449
Risk Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2014	54		54
2015	94		94
2016	77		77
2017	64		64
2018	53		53
Thereafter	104		104
Estimated future amortization for intangible assets	446		446
HR Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2014	124		124
2015	213		213
2016	178		178
2017	141		141
2018	94		94
Thereafter	253		253
Estimated future amortization for intangible assets	1,003		1,003
Customer related and contract based [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	2,788		2,788		2,720
Intangible assets with finite lives, Accumulated Amortization	1,469		1,469		1,310
Intangible assets, Net Carrying Amount	1,319		1,319		1,410
Marketing, technology and other [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	593		593		584
Intangible assets with finite lives, Accumulated Amortization	463		463		435
Intangible assets, Net Carrying Amount	$ 130		$ 130		$ 149