Goodwill and Other Intangible Assets Schedule of changes in the net carrying amount of goodwill by operating segment (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Changes in the net carrying amount of goodwill by operating segment (in millions)
Balance at the beginning of the period	$ 8,943	$ 8,770
Goodwill related to acquisitions	38	96
Goodwill related to disposals	(12)	(1)
Goodwill related to other prior year acquisitions	15	(6)
Transfers		0	[1]
Foreign currency translation	13	84
Balance at the end of the period	8,997	8,943
Risk Solutions [Member]
Changes in the net carrying amount of goodwill by operating segment (in millions)
Balance at the beginning of the period	5,982	5,557
Goodwill related to acquisitions	36	49
Goodwill related to disposals	(9)	(1)
Goodwill related to other prior year acquisitions	(2)	(6)
Transfers		313	[1]
Foreign currency translation	13	70
Balance at the end of the period	6,020	5,982
HR Solutions [Member]
Changes in the net carrying amount of goodwill by operating segment (in millions)
Balance at the beginning of the period	2,961	3,213
Goodwill related to acquisitions	2	47
Goodwill related to disposals	(3)	0
Goodwill related to other prior year acquisitions	17	0
Transfers		(313)	[1]
Foreign currency translation	0	14
Balance at the end of the period	$ 2,977	$ 2,961

[1] Effective January 1, 2012, the Health and Benefits Consulting business was transferred from the HR Solutions segment to the Risk Solutions segment.