Derivative Financial Instruments (Notional Value Of Outstanding Cash Flow Hedge Contracts By Year Of Maturity And Net Unrealized (Loss) Gain Included In Accumulated Other Comprehensive Income) (Details) - Cash Flow Hedges [Member] - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Derivative, notional amount	$ 1,905	$ 2,340
Net unrealized gains included in accumulated other comprehensive income (loss), net of taxes	115	39
Foreign Exchange Forward, Maturity 2017 [Member]
Derivative [Line Items]
Derivative, notional amount	0	1,320
Foreign Exchange Forward, Maturity 2018 [Member] [Member]
Derivative [Line Items]
Derivative, notional amount	1,185	1,020
Foreign Exchange Forward, Maturity 2019 [Member]
Derivative [Line Items]
Derivative, notional amount	$ 720	$ 0