Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets [Abstract]

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of intangible assets, excluding goodwill, acquired at the acquisition date.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
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-Section 50
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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of assets expected to be realized or consumed after one year or the normal operating cycle, if longer, acquired at the acquisition date.

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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.

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The number of businesses acquired by the entity during the period.

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Acquisitions and Dispositions of Businesses - Acquisitions (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) acquisition	Sep. 30, 2015 USD ($) acquisition	Sep. 30, 2016 USD ($) acquisition	Sep. 30, 2015 USD ($) acquisition	Dec. 31, 2015 USD ($)
Business Acquisition
Number of business acquired under business combination \| acquisition	1	1	5	5
Intangible assets:
Goodwill	$ 8,452		$ 8,452		$ 8,448
Business Acquisition 1 [Member]
Business Acquisition
Consideration	207	$ 26	207	$ 26
Intangible assets:
Goodwill	117	18	117	18
Other intangible assets	93	1	93	1
Total	$ 210	$ 19	$ 210	$ 19
Risk Solutions [Member]
Business Acquisition
Number of business acquired under business combination \| acquisition	1	0	3	2
Intangible assets:
Goodwill	$ 5,644		$ 5,644		5,593
HR Solutions [Member]
Business Acquisition
Number of business acquired under business combination \| acquisition	0	1	2	3
Intangible assets:
Goodwill	$ 2,808		$ 2,808		$ 2,855