Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Supplemental Cash Flow Information [Abstract]
Deferred and contingent consideration from prior years acquisition	$ 110	$ 125
Deferred purchase consideration from prior years' acquisitions	84	60
Contingent consideration from prior year's acquisitions	26	65
Contingent consideration from prior year's dispositions	71
Credit adjustment related to contingent consideration liabilities	(35)	22
Payment of contingent consideration	46	36
Adjustments related to contingent consideration receivable	24
Proceeds from contingent consideration, prior period dispositions	19
Non-cash issuance of common stock	225	217
Stock-based compensation expense, equity awards	$ 263	$ 219