Derivatives (Hedges of Net Investments in Foreign Operations) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Amount And Location Of Gains Losses Reclassified From Accumulated Other Comprehensive Income Loss Into Income Loss Effective Portion On Net Investment In Foreign Operation Hedges	$ 0		$ 0
Amount of Gains (Losses) Deferred in AOCI	414
Foreign Operations Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gains (Losses) Deferred in AOCI	(445)	$ (302)	117
Foreign Operations Hedges [Member] | Foreign currency forwards
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gains (Losses) Deferred in AOCI	(155)	(267)	255
Foreign Operations Hedges [Member] | Currency options
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gains (Losses) Deferred in AOCI	$ (290)	$ (35)	$ (138)