Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	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