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, 2023	Dec. 31, 2022
Derivatives, Fair Value
Derivative Assets	$ 3,307	$ 3,173
Derivative Liabilities	3,772	3,952
Amount of variation margin payment applied to derivative asset contracts	698	1,000
Amount of variation margin payment applied to derivative liability contracts	1,900	1,000
Designated as Hedging Instrument | Cash flow hedge derivatives
Derivatives, Fair Value
Derivative Assets	3	157
Derivative Liabilities	73	296
Designated as Hedging Instrument | Fair Value Hedging | Cash flow hedge derivatives
Derivatives, Fair Value
Derivative Assets	0	126
Derivative Liabilities	63	195
Designated as Hedging Instrument | Fair Value Hedging | Interest rate swap | Cash flow hedge derivatives | Long-term debt
Derivatives, Fair Value
Notional Amount	5,955	5,955
Derivative Assets	0	126
Derivative Liabilities	63	195
Designated as Hedging Instrument | Cash Flow Hedging | Cash flow hedge derivatives
Derivatives, Fair Value
Derivative Assets	3	31
Derivative Liabilities	10	101
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swap | Cash flow hedge derivatives | Commercial and industrial
Derivatives, Fair Value
Notional Amount	8,000	8,000
Derivative Assets	1	0
Derivative Liabilities	6	76
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swap | Cash flow hedge derivatives | Commercial mortgage and commercial construction
Derivatives, Fair Value
Notional Amount	4,000	4,000
Derivative Assets	2	0
Derivative Liabilities	0	25
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate floor | Cash flow hedge derivatives | Commercial and industrial
Derivatives, Fair Value
Notional Amount	3,000	3,000
Derivative Assets	0	4
Derivative Liabilities	0	0
Designated as Hedging Instrument | Cash Flow Hedging | Forward starting interest rate swap | Cash flow hedge derivatives | Commercial and industrial
Derivatives, Fair Value
Notional Amount	10,000	11,000
Derivative Assets	0	22
Derivative Liabilities	2	0
Designated as Hedging Instrument | Cash Flow Hedging | Forward starting interest rate swap | Cash flow hedge derivatives | Commercial mortgage and commercial construction
Derivatives, Fair Value
Notional Amount	4,000	4,000
Derivative Assets	0	5
Derivative Liabilities	2	0
Not Designated as Hedging Instrument
Derivatives, Fair Value
Derivative Assets	3,304	3,016
Derivative Liabilities	3,699	3,656
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes
Derivatives, Fair Value
Derivative Assets	87	85
Derivative Liabilities	184	220
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contracts related to MSR portfolio
Derivatives, Fair Value
Notional Amount	2,550	2,975
Derivative Assets	73	62
Derivative Liabilities	10	17
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Forward contracts related to residential mortgage loans held for sale | Loans held for sale
Derivatives, Fair Value
Notional Amount	869	1,869
Derivative Assets	12	9
Derivative Liabilities	1	7
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Swap
Derivatives, Fair Value
Notional Amount	3,691	3,358
Derivative Assets	0	0
Derivative Liabilities	172	195
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Foreign exchange contracts
Derivatives, Fair Value
Notional Amount	200	156
Derivative Assets	0	1
Derivative Liabilities	0	0
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest-only strips
Derivatives, Fair Value
Notional Amount	42	58
Derivative Assets	1	4
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	12,000	12,000
Derivative Assets	1	9
Derivative 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	0	0
Derivative Liabilities	0	0
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Other
Derivatives, Fair Value
Notional Amount	14
Derivative Assets	0
Derivative Liabilities	0
Not Designated as Hedging Instrument | Customer Accommodation
Derivatives, Fair Value
Derivative Assets	3,217	2,931
Derivative Liabilities	3,515	3,436
Not Designated as Hedging Instrument | Customer Accommodation | Foreign exchange contracts
Derivatives, Fair Value
Notional Amount	32,998	25,322
Derivative Assets	706	453
Derivative Liabilities	644	422
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate contracts for LIBOR transition
Derivatives, Fair Value
Notional Amount	1,300
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate contracts
Derivatives, Fair Value
Notional Amount	90,848	83,605
Derivative Assets	1,392	998
Derivative Liabilities	1,826	1,663
Amount of variation margin payment applied to derivative asset contracts	528	694
Amount of variation margin payment applied to derivative liability contracts	96	37
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate lock commitments
Derivatives, Fair Value
Notional Amount	355	216
Derivative Assets	4	2
Derivative Liabilities	0	1
Not Designated as Hedging Instrument | Customer Accommodation | Commodity contracts
Derivatives, Fair Value
Notional Amount	18,417	16,122
Derivative Assets	1,115	1,478
Derivative Liabilities	1,045	1,350
Not Designated as Hedging Instrument | Customer Accommodation | TBA securities
Derivatives, Fair Value
Notional Amount	60	62
Derivative Assets	0	0
Derivative Liabilities	$ 0	$ 0