Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Supplemental Cash Flow Information [Abstract]
Deferred and contingent consideration from prior years acquisition	$ 125	$ 60
Deferred purchase consideration from prior years' acquisitions	60	37
Contingent consideration from prior year's acquisitions	65	23
Expense for adjustments related to contingent consideration liabilities	22	26
Payment of contingent consideration	36	35
Non-cash issuance of common stock	217	164
Stock-based compensation expense, equity awards	$ 219	$ 184