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Supplemental Disclosures (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Supplemental Cash Flow Information [Abstract] |  |  |
Deferred and contingent purchase consideration from prior years' acquisition | $ 117 | $ 136 | $ 98
Deferred purchase consideration from prior years' acquisitions | 62 | 55 | 54
Contingent purchase consideration from prior years' acquisitions | 55 | 81 | 44
Net charge for adjustments related to acquisitions | 32 | 3 | 9
Payment of contingent consideration | 36 | 27 | 42
Non-cash issuance of common stock | 130 | 88 | 73
Stock-based compensation expense, equity awards | $ 193 | $ 149 | 109
Adjustments to additional paid in capital, income tax benefit from share-based compensation |  |  | $ 44

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