Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Supplemental Cash Flow Information [Abstract]
Deferred and contingent consideration from prior years acquisition	$ 97	$ 69
Deferred purchase consideration from prior years' acquisitions	84	27
Contingent consideration from prior year's acquisitions	13	42
Contingent consideration from prior year's dispositions	71
Credit adjustment related to contingent consideration liabilities	17	6
Payment of contingent consideration	4	36
Adjustments related to contingent consideration receivable	24
Proceeds from contingent consideration, prior period dispositions	18
Non-cash issuance of common stock	228	213
Stock-based compensation expense, equity awards	$ 176	$ 147