Goodwill and Other Intangible Assets (Details 2) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
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	4,472		4,472		4,446
Intangible assets with finite lives, Accumulated Amortization	2,434		2,434		2,266
Intangible assets, Net Carrying Amount	2,038		2,038		2,180
Amortization of intangible assets	72	$ 78	207	$ 237
Estimated amortization for intangible assets
Remainder of 2016	66		66
2017	233		233
2018	177		177
2019	149		149
2020	126		126
Thereafter	268		268
Total	1,019		1,019
Risk Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2016	26		26
2017	99		99
2018	87		87
2019	76		76
2020	66		66
Thereafter	155		155
Total	509		509
HR Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2016	40		40
2017	134		134
2018	90		90
2019	73		73
2020	60		60
Thereafter	113		113
Total	510		510
Customer related and contract based [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	2,913		2,913		2,886
Intangible assets with finite lives, Accumulated Amortization	1,945		1,945		1,809
Intangible assets, Net Carrying Amount	968		968		1,077
Technology and other [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	540		540		541
Intangible assets with finite lives, Accumulated Amortization	489		489		457
Intangible assets, Net Carrying Amount	$ 51		$ 51		$ 84