Derivative Financial Instruments - Notional Amounts and Fair Values for All Derivative Instruments Included in the Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Derivatives, Fair Value
Derivative assets	$ 2,098	$ 2,677
Derivative liabilities	2,427	2,999
Amount of variation margin payment applied to derivative asset contracts	(437)	(587)
Amount of variation margin payment applied to derivative liability contracts	437	721
Designated as Hedging Instrument
Derivatives, Fair Value
Derivative assets	0	10
Derivative liabilities	37	45
Designated as Hedging Instrument | Fair Value Hedging
Derivatives, Fair Value
Derivative assets	0	0
Derivative liabilities	27	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	0	0
Derivative liabilities	27	32
Designated as Hedging Instrument | Cash Flow Hedging
Derivatives, Fair Value
Derivative assets	0	10
Derivative liabilities	10	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	0	2
Derivative liabilities	10	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	0	1
Derivative liabilities	0	0
Designated as Hedging Instrument | Cash Flow Hedging | Forward starting interest rate swap | Commercial and industrial
Derivatives, Fair Value
Notional amount	4,000	6,000
Derivative assets	0	6
Derivative 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	0	1
Derivative liabilities	0	1
Not Designated as Hedging Instrument
Derivatives, Fair Value
Derivative assets	2,098	2,667
Derivative liabilities	2,390	2,954
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes
Derivatives, Fair Value
Derivative assets	13	83
Derivative liabilities	201	178
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contracts related to MSR portfolio
Derivatives, Fair Value
Notional amount	3,505	3,205
Derivative assets	11	81
Derivative 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	1,040	650
Derivative assets	1	0
Derivative liabilities	4	5
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Swap
Derivatives, Fair Value
Notional amount	2,206	4,178
Derivative assets	0	0
Derivative liabilities	196	168
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Foreign exchange contracts
Derivatives, Fair Value
Notional amount	175	190
Derivative assets	0	0
Derivative liabilities	0	4
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest-only strips
Derivatives, Fair Value
Notional amount	32	39
Derivative assets	1	1
Derivative 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	1,000	5,000
Derivative assets	0	1
Derivative liabilities	0	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	0	0
Derivative liabilities	0	0
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Other
Derivatives, Fair Value
Notional amount	41	30
Derivative assets	0	0
Derivative liabilities	0	0
Not Designated as Hedging Instrument | Customer Accommodation
Derivatives, Fair Value
Derivative assets	2,085	2,584
Derivative liabilities	2,189	2,776
Not Designated as Hedging Instrument | Customer Accommodation | Foreign exchange contracts
Derivatives, Fair Value
Notional amount	38,815	37,734
Derivative assets	739	643
Derivative liabilities	710	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	89,233	95,079
Derivative assets	628	885
Derivative liabilities	777	1,162
Amount of variation margin payment applied to derivative asset contracts	(190)	(335)
Amount of variation margin payment applied to derivative liability contracts	49	58
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate lock commitments
Derivatives, Fair Value
Notional amount	398	252
Derivative assets	6	5
Derivative liabilities	0	0
Not Designated as Hedging Instrument | Customer Accommodation | Commodity contracts
Derivatives, Fair Value
Notional amount	16,977	17,621
Derivative assets	712	1,051
Derivative liabilities	702	1,018
Not Designated as Hedging Instrument | Customer Accommodation | TBA securities
Derivatives, Fair Value
Notional amount	17	27
Derivative assets	0	0
Derivative liabilities	$ 0	$ 0