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Acquisitions and Investments - Additional Information (Detail) $ in Millions | 12 Months Ended
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Dec. 31, 2017 USD ($) Acquisition | Dec. 31, 2016 USD ($) Acquisition | Dec. 31, 2015 USD ($) Acquisition
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |
Aggregate cash investment of acquisitions | $ 86 | $ 230 | $ 86
Goodwill | $ 6,227 | $ 6,067 | $ 6,980
All Other Acquisitions [Member] |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |
Acquisitions completed | Acquisition | 8 | 10 | 7
Aggregate cash investment of acquisitions | $ 86 | $ 230 | $ 86
Intangible assets | 61 | 24 | 13
Goodwill | $ 89 | 74 | $ 51
Business acquisition Nov stock issued |  | $ 18 |

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