Goodwill and Other Intangible Assets (Details 2) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
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	4,501		4,501		4,542
Intangible assets with finite lives, Accumulated Amortization	2,151		2,151		2,022
Intangible assets, Net Carrying Amount	2,350		2,350		2,520
Amortization expense on intangible assets	79	$ 87	159	$ 173
Estimated amortization for intangible assets
Remainder of 2015	159		159
2016	276		276
2017	231		231
2018	170		170
2019	141		141
Thereafter	354		354
Total	1,331		1,331
Risk Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2015	56		56
2016	104		104
2017	93		93
2018	78		78
2019	68		68
Thereafter	188		188
Total	587		587
HR Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2015	103		103
2016	172		172
2017	138		138
2018	92		92
2019	73		73
Thereafter	166		166
Total	744		744
Customer related and contract based [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	2,930		2,930		2,952
Intangible assets with finite lives, Accumulated Amortization	1,706		1,706		1,579
Intangible assets, Net Carrying Amount	1,224		1,224		1,373
Marketing, technology and other [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	552		552		571
Intangible assets with finite lives, Accumulated Amortization	445		445		443
Intangible assets, Net Carrying Amount	$ 107		$ 107		$ 128