Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Supplemental Disclosure to the Consolidate Statements of Cash Flows [Line Items]
Deferred and contingent consideration from prior years acquisition	$ 70	$ 34
Contingent consideration from prior year's acquisitions	30	8
Net charge for adjustments related to acquisition related accounts	5	(16)
Payment of contingent consideration	10	4
Non-cash issuance of common stock	125	85
Stock-based compensation expense, equity awards	50	42
Prior Fiscal Periods Acquisitions
Supplemental Disclosure to the Consolidate Statements of Cash Flows [Line Items]
Deferred purchase consideration from prior years' acquisitions	40	26
Contingent consideration from prior year's acquisitions	$ 40	$ 12