Derivative Financial Instruments - Total Notional or Contractual Amounts, Fair Value, Collateral and Net Exposure of Derivative Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Derivative Assets	$ 314	$ 285
Derivative Liabilities	274	237
Derivative Assets, Total	588	488
Derivative Liabilities, Total	274	237
Reduction in derivative liabilities due to rules of clearing houses	5	45
Interest rate swaps
Derivative [Line Items]
Derivative Assets	14	0
Derivative Liabilities	0	0
Foreign exchange forwards and swaps
Derivative [Line Items]
Derivative Assets	183	215
Derivative Liabilities	156	208
Client foreign currency options
Derivative [Line Items]
Derivative Assets	2	2
Derivative Liabilities	2	2
Client interest rate derivatives
Derivative [Line Items]
Derivative Assets	115	68
Derivative Liabilities	116	27
Derivatives designated as hedging instruments | Interest rate swaps | Other assets
Derivative [Line Items]
Derivative Asset, Notional or Contractual Amount	9,175	0
Derivative Assets	14	0
Derivatives designated as hedging instruments | Interest rate swaps | Other liabilities
Derivative [Line Items]
Derivative Liabilities, Notional or Contractual Amount	2,125	0
Derivative Liabilities	0	0
Derivatives not designated as hedging instruments
Derivative [Line Items]
Derivative Assets	574	488
Derivative Liabilities	274	237
Derivatives not designated as hedging instruments | Foreign exchange forwards and swaps | Other assets
Derivative [Line Items]
Derivative Asset, Notional or Contractual Amount	651	68
Derivative Liabilities	12	0
Derivatives not designated as hedging instruments | Foreign exchange forwards and swaps | Other liabilities
Derivative [Line Items]
Derivative Liabilities, Notional or Contractual Amount	80	567
Derivative Liabilities	1	20
Derivatives not designated as hedging instruments | Equity warrant assets | Other assets
Derivative [Line Items]
Derivative Asset, Notional or Contractual Amount	309	253
Derivative Assets	274	203
Derivatives not designated as hedging instruments | Client foreign exchange forwards and swaps | Other assets
Derivative [Line Items]
Derivative Asset, Notional or Contractual Amount	8,974	8,026
Derivative Assets	171	215
Derivatives not designated as hedging instruments | Client foreign exchange forwards and swaps | Other liabilities
Derivative [Line Items]
Derivative Liabilities, Notional or Contractual Amount	8,652	7,491
Derivative Liabilities	155	188
Derivatives not designated as hedging instruments | Client foreign currency options | Other assets
Derivative [Line Items]
Derivative Asset, Notional or Contractual Amount	196	98
Derivative Assets	2	2
Derivatives not designated as hedging instruments | Client foreign currency options | Other liabilities
Derivative [Line Items]
Derivative Liabilities, Notional or Contractual Amount	196	98
Derivative Liabilities	2	2
Derivatives not designated as hedging instruments | Client interest rate derivatives | Other assets
Derivative [Line Items]
Derivative Asset, Notional or Contractual Amount	2,249	1,082
Derivative Assets	115	68
Derivatives not designated as hedging instruments | Client interest rate derivatives | Other liabilities
Derivative [Line Items]
Derivative Liabilities, Notional or Contractual Amount	2,264	1,251
Derivative Liabilities	$ 116	$ 27