Goodwill and Other Intangible Assets (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2013
Changes in the net carrying amount of goodwill by operating segment (in millions)
Balance as of December 31, 2012	$ 8,943
Goodwill related to current year acquisitions	26
Goodwill related to disposals	(3)
Goodwill related to prior year acquisitions	15
Foreign currency translation	(23)
Balance as of September 30, 2013	8,958
Risk Solutions [Member]
Changes in the net carrying amount of goodwill by operating segment (in millions)
Balance as of December 31, 2012	5,982
Goodwill related to current year acquisitions	24
Goodwill related to disposals	(3)
Goodwill related to prior year acquisitions	(2)
Foreign currency translation	(19)
Balance as of September 30, 2013	5,982
HR Solutions [Member]
Changes in the net carrying amount of goodwill by operating segment (in millions)
Balance as of December 31, 2012	2,961
Goodwill related to current year acquisitions	2
Goodwill related to disposals	0
Goodwill related to prior year acquisitions	17
Foreign currency translation	(4)
Balance as of September 30, 2013	$ 2,976

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 25

-Paragraph 16

-URI http://asc.fasb.org/extlink&oid=21917927&loc=d3e961-128460

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Amount of increase (decrease) from foreign currency translation adjustments of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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