Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	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