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Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Mar. 31, 2019 | Jun. 30, 2019 | Jun. 30, 2018
Supplemental Cash Flow Information [Abstract] |  |  |
Deferred and contingent consideration from prior years acquisition |  | $ 39 | $ 85
Deferred purchase consideration from prior years' acquisitions |  |  | 53
Contingent consideration from prior year's acquisitions |  | 16 | 32
Net charge for adjustments related to acquisition related accounts |  | 20 | 11
Payment of contingent consideration |  | 29 | 9
Non-cash issuance of common stock |  | 162 | 128
Stock-based compensation expense, equity awards |  | $ 117 | $ 99
Right-of-use asset, noncash | $ 1,700 |  |
Right-to-use liability, noncash | $ 1,900 |  |

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