Derivative Financial Instruments - Gains and Losses on Derivative Instruments Held For Other Purpose (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Derivatives, Fair Value [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives held for other purposes	$ 340	$ 165
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member]
Derivatives, Fair Value [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives held for other purposes	357	161
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member] | Interest rate contracts [Member]
Derivatives, Fair Value [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives held for other purposes	3	214
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member] | Foreign exchange contracts [Member]
Derivatives, Fair Value [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives held for other purposes	9	12
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member] | Equity contracts [Member]
Derivatives, Fair Value [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives held for other purposes	360	(49)
Other Income [Member] | Credit contracts [Member]
Derivatives, Fair Value [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives held for other purposes	$ (32)	$ (12)