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Supplemental Disclosures (Schedule of Supplemental Cash Flow Disclosures) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Supplemental Cash Flow Information [Abstract] |  |  |
Assets acquired, excluding cash | $ 1,100 | $ 898 | $ 960
Liabilities assumed | (83) | (134) | (111)
Contingent/deferred purchase consideration | (133) | (109) | (36)
Net cash outflow for acquisitions | 884 | 655 | 813
Interest paid | 264 | 199 | 178
Income taxes paid, net of refunds | $ 632 | $ 583 | $ 642

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