Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Supplemental Cash Flow Information [Abstract]
Deferred and contingent consideration from prior years acquisition	$ 37	$ 29
Deferred purchase consideration from prior years' acquisitions	27	25
Contingent consideration from prior year's acquisitions	10	4
Contingent consideration from prior year's dispositions	5
Payment of contingent consideration	1	9
Credit adjustment related to contingent consideration liabilities		1
Non-cash issuance of common stock	212	201
Stock-based compensation expense, equity awards	$ 78	$ 72