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Acquisitions and Dispositions of Businesses - Acquisitions (Details) $ in Millions | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2018 USD ($) acquisition | Dec. 31, 2017 USD ($) acquisition
Business Acquisition |  |
Number of business acquired under business combination | acquisition | 5 | 17
Assets acquired: |  |
Goodwill | $ 8,291 | $ 8,358
2018 Acquisitions |  |
Business Combination, Consideration Transferred [Abstract] |  |
Cash | 45 |
Deferred and contingent consideration | 14 |
Aggregate consideration transferred | 59 |
Assets acquired: |  |
Receivables, net | 2 |
Goodwill | 31 |
Intangible assets, net | 28 |
Other assets | 3 |
Total assets acquired | 64 |
Liabilities assumed: |  |
Current liabilities | 4 |
Other non-current liabilities | 1 |
Total liabilities assumed | 5 |
Net assets acquired | $ 59 |

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