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Acquisitions and Dispositions - Acquisitions (Details) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2015 USD ($) acquisition | Dec. 31, 2014 USD ($) acquisition | Dec. 31, 2013 USD ($)
Business Acquisition |  |  |
Number of business acquired under business combination | acquisition | 7 | 13 |
Goodwill | $ 8,448 | $ 8,860 | $ 8,997
Risk Solutions [Member] |  |  |
Business Acquisition |  |  |
Number of business acquired under business combination | acquisition | 4 | 11 |
Goodwill | $ 5,593 | $ 5,911 | 6,020
HR Solutions [Member] |  |  |
Business Acquisition |  |  |
Number of business acquired under business combination | acquisition | 3 | 2 |
Goodwill | $ 2,855 | $ 2,949 | $ 2,977
Business Acquisitions [Member] |  |  |
Business Acquisition |  |  |
Consideration | 27 | 461 |
Goodwill | 18 | 292 |
Other intangible assets | 6 | 328 |
Total intangible assets | $ 24 | $ 620 |

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