Fair Value Measurements (Valuation Of Financial Instruments By Pricing Categories) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 1,641	$ 2,542	$ 3,649	$ 3,316
Assets
Available-for-sale securities, current	279	251
Investments Fair Value Disclosure	2,125	2,978
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration [Abstract]
Financial and Nonfinancial Liabilities, Fair Value Disclosure	247	190
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	1,641	2,542
Assets
Investments Fair Value Disclosure	1,770	2,663
Deferred compensation arrangements	129	121
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration [Abstract]
Financial and Nonfinancial Liabilities, Fair Value Disclosure	129	121
Fair Value, Inputs, Level 1 | Trading marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading marketable securities	129	121
Fair Value, Inputs, Level 2
Assets
Investments Fair Value Disclosure	355	315
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration [Abstract]
Financial and Nonfinancial Liabilities, Fair Value Disclosure	13	37
Fair Value, Inputs, Level 2 | Foreign currency exchange forward contracts
Assets
Derivative asset	76	15
Liabilities
Foreign currency exchange forward contracts	13	37
Fair Value, Inputs, Level 2 | Interest rate swap asset
Assets
Derivative asset	0	49
Fair Value, Inputs, Level 2 | Available-for-sale marketable securities:
Assets
Available-for-sale securities, current	279	251
Fair Value, Inputs, Level 2 | Available-for-sale marketable securities: | Corporate and asset-backed debt securities
Assets
Available-for-sale securities, current	99	125
Fair Value, Inputs, Level 2 | Available-for-sale marketable securities: | Foreign government debt securities
Assets
Available-for-sale securities, current	2	2
Fair Value, Inputs, Level 2 | Available-for-sale marketable securities: | United States agency debt securities
Assets
Available-for-sale securities, current	32	27
Fair Value, Inputs, Level 2 | Available-for-sale marketable securities: | United States Treasury debt securities
Assets
Available-for-sale securities, current	77	70
Fair Value, Inputs, Level 2 | Available-for-sale marketable securities: | Certificates of deposit
Assets
Available-for-sale securities, current	69	27
Fair Value, Inputs, Level 3
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration [Abstract]
Beginning	32	86
Additions	78	3
Change in estimate	(1)	2
Settlements	(4)	(59)
Ending	105	32
Financial and Nonfinancial Liabilities, Fair Value Disclosure	$ 105	$ 32