Derivative Financial Instruments - Schedule of The Fair Values of Derivative Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	$ 13,371	$ 16,552
Fair value of derivative liabilities	13,792	16,684
Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	13,371	16,484
Fair value of derivative liabilities	13,312	15,956
Interest-rate contracts(6)
Derivatives, Fair Value [Line Items]
Fair value of derivative assets		68
Fair value of derivative liabilities	124	348
Derivatives not designated as hedging instruments | Other Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	13,323	15,982
Derivatives not designated as hedging instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	13,522	16,261
Derivatives not designated as hedging instruments | Foreign exchange contracts | Other Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	13,323	15,982
Derivatives not designated as hedging instruments | Foreign exchange contracts | Other liabilities
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	13,166	15,881
Derivatives not designated as hedging instruments | Other derivative contracts | Other liabilities
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	356	380
Derivatives designated as hedging instruments | Other Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	48	570
Derivatives designated as hedging instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	270	423
Derivatives designated as hedging instruments | Foreign exchange contracts | Other Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	48	502
Derivatives designated as hedging instruments | Foreign exchange contracts | Other liabilities
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	146	75
Derivatives designated as hedging instruments | Interest-rate contracts(6) | Other Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	0	68
Derivatives designated as hedging instruments | Interest-rate contracts(6) | Other liabilities
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	$ 124	$ 348