Acquisitions and Dispositions (Allocation Of Acquisition Costs) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Cash	$ 405	$ 579
Estimated fair value of deferred/contingent consideration	141	163
Total consideration	546	742
Allocation of purchase price:
Goodwill	15,648	$ 15,034	$ 15,517	$ 14,671
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Cash	405
Estimated fair value of deferred/contingent consideration	141
Total consideration	546
Allocation of purchase price:
Cash and cash equivalents	4
Accounts receivable, net	32
Fixed assets, net	5
Other intangible assets	190
Goodwill	374
Total assets acquired	605
Current liabilities	27
Other liabilities	32
Total liabilities assumed	59
Net assets acquired	$ 546