Derivative Financial Instruments And Hedging Activities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Apr. 01, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Notional forward foreign exchange contracts outstanding	$ 4,600	$ 5,800
Average maturity of foreign currency forward contracts, in years	2 years
Cash and equivalents	$ 673	963	$ 4,332	$ 2,983
Marketable securities held in trust	$ 199	$ 202
Maximum
Derivative Instruments, Gain (Loss) [Line Items]
Maturity of fixed-income securities, in years	5 years