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Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions | 9 Months Ended
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Sep. 30, 2020 | Sep. 30, 2019
Supplemental Cash Flow Information [Abstract] |  |
Deferred and contingent consideration from prior years acquisition | $ 125 | $ 60
Deferred purchase consideration from prior years' acquisitions | 60 | 37
Contingent consideration from prior year's acquisitions | 65 | 23
Expense for adjustments related to contingent consideration liabilities | 22 | 26
Payment of contingent consideration | 36 | 35
Non-cash issuance of common stock | 217 | 164
Stock-based compensation expense, equity awards | $ 219 | $ 184

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