Acquisitions (Allocation Of Acquisition Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Cash	$ 29	$ 419
Estimated fair value of deferred/contingent consideration	7	90
Total Consideration	36	509
Allocation of purchase price:
Goodwill	9,194	$ 8,769	$ 9,089	$ 8,369
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Cash	29
Estimated fair value of deferred/contingent consideration	7
Total Consideration	36
Allocation of purchase price:
Cash and cash equivalents	5
Accounts receivable, net	3
Other intangible assets	13
Goodwill	15
Other assets	4
Total assets acquired	40
Current liabilities	3
Other liabilities	1
Total liabilities assumed	4
Net assets acquired	$ 36