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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, 2018 | Sep. 30, 2017
Supplemental Disclosure to the Consolidate Statements of Cash Flows [Line Items] |  |
Deferred and contingent consideration from prior years acquisition | $ 106 | $ 127
Contingent consideration from prior year's acquisitions | 47 | 80
Net charge for adjustments related to acquisition related accounts |  | (3)
Payment of contingent consideration | 29 | 27
Non-cash issuance of common stock | 129 | 88
Stock-based compensation expense, equity awards | 146 | 111
Prior Fiscal Periods Acquisitions |  |
Supplemental Disclosure to the Consolidate Statements of Cash Flows [Line Items] |  |
Deferred purchase consideration from prior years' acquisitions | 59 | 47
Contingent consideration from prior year's acquisitions | $ 76 | $ 107

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