Derivative Financial Instruments - Schedule of The Fair Values of Derivative Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	$ 16,905	$ 15,148
Fair value of derivative liabilities	15,700	15,381
Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	16,905	15,140
Fair value of derivative liabilities	15,472	15,150
Interest rate contracts
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	0	8
Fair value of derivative liabilities	52	49
Derivatives not designated as hedging instruments | Other Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	16,866	15,140
Derivatives not designated as hedging instruments | Other Liabilities
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	15,628	15,236
Derivatives not designated as hedging instruments | Foreign exchange contracts | Other Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	16,866	15,140
Derivatives not designated as hedging instruments | Foreign exchange contracts | Other Liabilities
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	15,452	15,054
Derivatives not designated as hedging instruments | Other derivative contracts | Other Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	0	0
Derivatives not designated as hedging instruments | Other derivative contracts | Other Liabilities
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	176	182
Derivatives designated as hedging instruments | Other Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	39	8
Derivatives designated as hedging instruments | Other Liabilities
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	73	145
Derivatives designated as hedging instruments | Foreign exchange contracts | Other Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	39	0
Derivatives designated as hedging instruments | Foreign exchange contracts | Other Liabilities
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	20	96
Derivatives designated as hedging instruments | Interest rate contracts | Other Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	0	8
Derivatives designated as hedging instruments | Interest rate contracts | Other Liabilities
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	$ 53	$ 49