Goodwill and Other Intangible Assets (Details 2) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 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	4,484		4,484		4,446
Intangible assets with finite lives, Accumulated Amortization	2,377		2,377		2,266
Intangible assets, Net Carrying Amount	2,107		2,107		2,180
Amortization expense on intangible assets	68	$ 79	135	$ 159
Estimated amortization for intangible assets
Remainder of 2016	147		147
2017	228		228
2018	172		172
2019	145		145
2020	123		123
Thereafter	273		273
Total	1,088		1,088
Risk Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2016	44		44
2017	81		81
2018	73		73
2019	66		66
2020	58		58
Thereafter	157		157
Total	479		479
HR Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2016	103		103
2017	147		147
2018	99		99
2019	79		79
2020	65		65
Thereafter	116		116
Total	609		609
Customer related and contract based [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	2,923		2,923		2,886
Intangible assets with finite lives, Accumulated Amortization	1,899		1,899		1,809
Intangible assets, Net Carrying Amount	1,024		1,024		1,077
Technology and other [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	542		542		541
Intangible assets with finite lives, Accumulated Amortization	478		478		457
Intangible assets, Net Carrying Amount	$ 64		$ 64		$ 84