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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, 2018 | Jun. 30, 2017
Supplemental Disclosure to the Consolidate Statements of Cash Flows [Line Items] |  |
Deferred and contingent consideration from prior years acquisition | $ 85 | $ 97
Contingent consideration from prior year's acquisitions | 32 | 60
Net charge for adjustments related to acquisition related accounts | 11 | (8)
Payment of contingent consideration | 9 | 5
Non-cash issuance of common stock | 128 | 87
Stock-based compensation expense, equity awards | 99 | 75
Prior Fiscal Periods Acquisitions |  |
Supplemental Disclosure to the Consolidate Statements of Cash Flows [Line Items] |  |
Deferred purchase consideration from prior years' acquisitions | 53 | 37
Contingent consideration from prior year's acquisitions | $ 41 | $ 65

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