Derivative Financial Instruments - Notional Amounts and Fair Values for All Derivative Instruments Included in the Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Derivatives, Fair Value
Derivative assets, fair value, gross assets	$ 2,855	$ 2,672
Derivative liabilities, fair value, gross liabilities	3,283	2,999
Derivative assets	2,860	2,677
Derivative liabilities	3,283	2,999
Amount of variation margin payment applied to derivative asset contracts	511	587
Amount of variation margin payment applied to derivative liability contracts	1,200	721
Designated as Hedging Instrument
Derivatives, Fair Value
Derivative assets, fair value, gross assets	1	10
Derivative liabilities, fair value, gross liabilities	56	45
Designated as Hedging Instrument | Fair Value Hedging
Derivatives, Fair Value
Derivative assets, fair value, gross assets	1	0
Derivative liabilities, fair value, gross liabilities	42	32
Designated as Hedging Instrument | Fair Value Hedging | Interest rate swap | Long-term debt
Derivatives, Fair Value
Notional amount	5,955	5,955
Derivative assets, fair value, gross assets	1	0
Derivative liabilities, fair value, gross liabilities	42	32
Designated as Hedging Instrument | Cash Flow Hedging
Derivatives, Fair Value
Derivative assets, fair value, gross assets	0	10
Derivative liabilities, fair value, gross liabilities	14	13
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swap | Commercial and industrial
Derivatives, Fair Value
Notional amount	8,000	8,000
Derivative assets, fair value, gross assets	0	2
Derivative liabilities, fair value, gross liabilities	13	11
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate floor | Commercial and industrial
Derivatives, Fair Value
Notional amount	3,000	3,000
Derivative assets, fair value, gross assets	0	1
Derivative liabilities, fair value, gross liabilities	0	0
Designated as Hedging Instrument | Cash Flow Hedging | Forward starting interest rate swap | Commercial and industrial
Derivatives, Fair Value
Notional amount	5,000	6,000
Derivative assets, fair value, gross assets	0	6
Derivative liabilities, fair value, gross liabilities	1	1
Designated as Hedging Instrument | Cash Flow Hedging | Forward starting interest rate swap | Commercial mortgage and commercial construction
Derivatives, Fair Value
Notional amount	4,000	4,000
Derivative assets, fair value, gross assets	0	1
Derivative liabilities, fair value, gross liabilities	0	1
Not Designated as Hedging Instrument
Derivatives, Fair Value
Derivative assets	2,859	2,667
Derivative liabilities	3,227	2,954
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes
Derivatives, Fair Value
Derivative assets, fair value, gross assets	24	83
Derivative liabilities, fair value, gross liabilities	172	178
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contracts related to MSR portfolio
Derivatives, Fair Value
Notional amount	3,180	3,205
Derivative assets, fair value, gross assets	20	81
Derivative liabilities, fair value, gross liabilities	1	0
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Forward contracts related to residential mortgage loans measured at fair value | Loans Measured At Fair Value
Derivatives, Fair Value
Notional amount	1,271	650
Derivative assets, fair value, gross assets	2	0
Derivative liabilities, fair value, gross liabilities	5	5
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Swap
Derivatives, Fair Value
Notional amount	2,808	4,178
Derivative assets, fair value, gross assets	0	0
Derivative liabilities, fair value, gross liabilities	164	168
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Foreign exchange contracts
Derivatives, Fair Value
Notional amount	218	190
Derivative assets, fair value, gross assets	1	0
Derivative liabilities, fair value, gross liabilities	0	4
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest-only strips
Derivatives, Fair Value
Notional amount	34	39
Derivative assets, fair value, gross assets	1	1
Derivative liabilities, fair value, gross liabilities	0	0
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contracts for collateral management
Derivatives, Fair Value
Notional amount	3,000	5,000
Derivative assets, fair value, gross assets	0	1
Derivative liabilities, fair value, gross liabilities	1	1
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contracts for LIBOR transition
Derivatives, Fair Value
Notional amount	597	597
Derivative assets, fair value, gross assets	0	0
Derivative liabilities, fair value, gross liabilities	0	0
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Other
Derivatives, Fair Value
Notional amount	38	30
Derivative assets, fair value, gross assets	0	0
Derivative liabilities, fair value, gross liabilities	1	0
Not Designated as Hedging Instrument | Customer Accommodation
Derivatives, Fair Value
Derivative assets	2,835	2,584
Derivative liabilities	3,055	2,776
Not Designated as Hedging Instrument | Customer Accommodation | Foreign exchange contracts
Derivatives, Fair Value
Notional amount	39,512	37,734
Derivative assets, fair value, gross assets	1,127	643
Derivative liabilities, fair value, gross liabilities	1,092	596
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate contracts for LIBOR transition
Derivatives, Fair Value
Notional amount	675	675
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate contracts
Derivatives, Fair Value
Notional amount	91,331	95,079
Derivative assets, fair value, gross assets	920	885
Derivative liabilities, fair value, gross liabilities	1,190	1,162
Amount of variation margin payment applied to derivative asset contracts	336	335
Amount of variation margin payment applied to derivative liability contracts	62	58
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate lock commitments
Derivatives, Fair Value
Notional amount	446	252
Derivative assets, fair value, gross assets	5	5
Derivative liabilities, fair value, gross liabilities	0	0
Not Designated as Hedging Instrument | Customer Accommodation | Commodity contracts
Derivatives, Fair Value
Notional amount	17,544	17,621
Derivative assets, fair value, gross assets	783	1,051
Derivative liabilities, fair value, gross liabilities	773	1,018
Not Designated as Hedging Instrument | Customer Accommodation | TBA securities
Derivatives, Fair Value
Notional amount	51	27
Derivative assets, fair value, gross assets	0	0
Derivative liabilities, fair value, gross liabilities	$ 0	$ 0