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Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions | 6 Months Ended
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Jun. 30, 2020 | Jun. 30, 2019
Supplemental Cash Flow Information [Abstract] |  |
Deferred and contingent consideration from prior years acquisition | $ 69 | $ 39
Deferred purchase consideration from prior years' acquisitions | 27 | 23
Contingent consideration from prior year's acquisitions | 42 | 16
Expense for adjustments related to contingent consideration liabilities | 6 | 20
Payment of contingent consideration | 36 | 29
Non-cash issuance of common stock | 213 | 162
Stock-based compensation expense, equity awards | $ 147 | $ 117

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