Goodwill and Other Intangible Assets (Details 2) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 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	4,459		4,459		4,542
Intangible assets with finite lives, Accumulated Amortization	2,202		2,202		2,022
Intangible assets, Net Carrying Amount	2,257		2,257		2,520
Amortization expense on intangible assets	78	$ 90	237	$ 263
Estimated amortization for intangible assets
Remainder of 2015	79		79
2016	272		272
2017	228		228
2018	169		169
2019	140		140
Thereafter	350		350
Total	1,238		1,238
Risk Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2015	51		51
2016	172		172
2017	137		137
2018	91		91
2019	72		72
Thereafter	164		164
Total	687		687
HR Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2015	28		28
2016	100		100
2017	91		91
2018	78		78
2019	68		68
Thereafter	186		186
Total	551		551
Customer related and contract based [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	2,899		2,899		2,952
Intangible assets with finite lives, Accumulated Amortization	1,753		1,753		1,579
Intangible assets, Net Carrying Amount	1,146		1,146		1,373
Technology and other [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	541		541		571
Intangible assets with finite lives, Accumulated Amortization	449		449		443
Intangible assets, Net Carrying Amount	$ 92		$ 92		$ 128