Goodwill and Other Intangible Assets (Details 2) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Intangible assets with indefinite lives
Tradenames	$ 1,019		$ 1,019
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	4,425		4,446
Intangible assets with finite lives, Accumulated Amortization	2,317		2,266
Intangible assets, Net Carrying Amount	2,108		2,180
Amortization expense on intangible assets	67	$ 80
Estimated amortization for intangible assets
Remainder of 2016	200
2017	225
2018	168
2019	140
2020	119
Thereafter	237
Total	1,089
Risk Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2016	72
2017	88
2018	77
2019	67
2020	59
Thereafter	123
Total	486
HR Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2016	128
2017	137
2018	91
2019	73
2020	60
Thereafter	114
Total	603
Customer related and contract based [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	2,871		2,886
Intangible assets with finite lives, Accumulated Amortization	1,851		1,809
Intangible assets, Net Carrying Amount	1,020		1,077
Technology and other [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	535		541
Intangible assets with finite lives, Accumulated Amortization	466		457
Intangible assets, Net Carrying Amount	$ 69		$ 84