Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Supplemental Cash Flow Information [Abstract]
Deferred and contingent consideration from prior years acquisition	$ 69	$ 39
Deferred purchase consideration from prior years' acquisitions	27	23
Contingent consideration from prior year's acquisitions	42	16
Expense for adjustments related to contingent consideration liabilities	6	20
Payment of contingent consideration	36	29
Non-cash issuance of common stock	213	162
Stock-based compensation expense, equity awards	$ 147	$ 117