Derivative Financial Instruments - Notional Amounts and Fair Values for All Derivative Instruments Included in the Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Derivatives, Fair Value
Derivative assets, fair value, gross assets	$ 2,772	$ 2,672
Derivative liabilities, fair value, gross liabilities	3,223	2,999
Derivative assets	2,777	2,677
Derivative liabilities	3,223	2,999
Amount of variation margin payment applied to derivative asset contracts	576	587
Amount of variation margin payment applied to derivative liability contracts	1,100	721
Designated as Hedging Instrument
Derivatives, Fair Value
Derivative assets, fair value, gross assets	5	10
Derivative liabilities, fair value, gross liabilities	39	45
Designated as Hedging Instrument | Fair Value Hedging
Derivatives, Fair Value
Derivative assets, fair value, gross assets	0	0
Derivative liabilities, fair value, gross liabilities	35	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	0	0
Derivative liabilities, fair value, gross liabilities	35	32
Designated as Hedging Instrument | Cash Flow Hedging
Derivatives, Fair Value
Derivative assets, fair value, gross assets	5	10
Derivative liabilities, fair value, gross liabilities	4	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	2	2
Derivative liabilities, fair value, gross liabilities	4	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	6,000	6,000
Derivative assets, fair value, gross assets	2	6
Derivative liabilities, fair value, gross liabilities	0	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	1	1
Derivative liabilities, fair value, gross liabilities	0	1
Not Designated as Hedging Instrument
Derivatives, Fair Value
Derivative assets	2,772	2,667
Derivative liabilities	3,184	2,954
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes
Derivatives, Fair Value
Derivative assets, fair value, gross assets	17	83
Derivative liabilities, fair value, gross liabilities	167	178
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contracts related to MSR portfolio
Derivatives, Fair Value
Notional amount	3,005	3,205
Derivative assets, fair value, gross assets	13	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	1,310	650
Derivative assets, fair value, gross assets	2	0
Derivative liabilities, fair value, gross liabilities	3	5
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Swap
Derivatives, Fair Value
Notional amount	4,478	4,178
Derivative assets, fair value, gross assets	0	0
Derivative liabilities, fair value, gross liabilities	162	168
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Foreign exchange contracts
Derivatives, Fair Value
Notional amount	200	190
Derivative assets, fair value, gross assets	0	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	37	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	5,000	5,000
Derivative assets, fair value, gross assets	1	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	32	30
Derivative assets, fair value, gross assets	0	0
Derivative liabilities, fair value, gross liabilities	0	0
Not Designated as Hedging Instrument | Customer Accommodation
Derivatives, Fair Value
Derivative assets	2,755	2,584
Derivative liabilities	3,017	2,776
Not Designated as Hedging Instrument | Customer Accommodation | Foreign exchange contracts
Derivatives, Fair Value
Notional amount	36,615	37,734
Derivative assets, fair value, gross assets	784	643
Derivative liabilities, fair value, gross liabilities	750	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	95,913	95,079
Derivative assets, fair value, gross assets	967	885
Derivative liabilities, fair value, gross liabilities	1,268	1,162
Amount of variation margin payment applied to derivative asset contracts	371	335
Amount of variation margin payment applied to derivative liability contracts	67	58
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate lock commitments
Derivatives, Fair Value
Notional amount	259	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	17,725	17,621
Derivative assets, fair value, gross assets	999	1,051
Derivative liabilities, fair value, gross liabilities	999	1,018
Not Designated as Hedging Instrument | Customer Accommodation | TBA securities
Derivatives, Fair Value
Notional amount	30	27
Derivative assets, fair value, gross assets	0	0
Derivative liabilities, fair value, gross liabilities	$ 0	$ 0