Derivative Financial Instruments - Total Notional or Contractual Amounts, Fair Value, Collateral and Net Exposure of Derivative Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Derivative Assets	$ 258	$ 285
Derivative Liabilities	218	237
Derivative Assets, Total	524	488
Derivative Liabilities, Total	218	237
Reduction in derivative liabilities due to rules of clearing houses	6	45
Interest rate swaps
Derivative [Line Items]
Derivative Assets	16	0
Derivative Liabilities	2	0
Foreign exchange forwards
Derivative [Line Items]
Derivative Assets	175	215
Derivative Liabilities	155	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	65	68
Derivative Liabilities	59	27
Derivatives designated as hedging instruments | Interest rate swaps | Other assets
Derivative [Line Items]
Derivative Asset, Notional or Contractual Amount	9,775	0
Derivative Assets	16	0
Derivatives designated as hedging instruments | Interest rate swaps | Other liabilities
Derivative [Line Items]
Derivative Liabilities, Notional or Contractual Amount	3,025	0
Derivative Liabilities	2	0
Derivatives not designated as hedging instruments
Derivative [Line Items]
Derivative Assets	508	488
Derivative Liabilities	216	237
Derivatives not designated as hedging instruments | Foreign exchange forwards | Other assets
Derivative [Line Items]
Derivative Asset, Notional or Contractual Amount	616	68
Derivative Liabilities	10	0
Derivatives not designated as hedging instruments | Foreign exchange forwards | Other liabilities
Derivative [Line Items]
Derivative Liabilities, Notional or Contractual Amount	184	567
Derivative Liabilities	2	20
Derivatives not designated as hedging instruments | Equity warrant assets | Other assets
Derivative [Line Items]
Derivative Asset, Notional or Contractual Amount	301	253
Derivative Assets	266	203
Derivatives not designated as hedging instruments | Client foreign exchange forwards | Other assets
Derivative [Line Items]
Derivative Asset, Notional or Contractual Amount	11,234	8,026
Derivative Assets	165	215
Derivatives not designated as hedging instruments | Client foreign exchange forwards | Other liabilities
Derivative [Line Items]
Derivative Liabilities, Notional or Contractual Amount	10,717	7,491
Derivative Liabilities	153	188
Derivatives not designated as hedging instruments | Client foreign currency options | Other assets
Derivative [Line Items]
Derivative Asset, Notional or Contractual Amount	233	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	233	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	1,306	1,082
Derivative Assets	65	68
Derivatives not designated as hedging instruments | Client interest rate derivatives | Other liabilities
Derivative [Line Items]
Derivative Liabilities, Notional or Contractual Amount	1,483	1,251
Derivative Liabilities	$ 59	$ 27