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, 2022	Dec. 31, 2021
Derivatives, Fair Value
Derivative Assets	$ 4,270	$ 2,908
Derivative Liabilities	4,241	2,013
Amount of variation margin payment applied to derivative asset contracts	759	771
Amount of variation margin payment applied to derivative liability contracts	465	570
Designated as Hedging Instrument | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Derivative Assets	312	522
Derivative Liabilities	44	3
Designated as Hedging Instrument | Fair Value Hedging | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Derivative Assets	266	400
Derivative Liabilities	27	2
Designated as Hedging Instrument | Fair Value Hedging | Interest rate swap | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Available-for-sale debt and other securities
Derivatives, Fair Value
Notional Amount		445
Derivative Assets		7
Derivative Liabilities		0
Designated as Hedging Instrument | Fair Value Hedging | Interest rate swap | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Long-term debt
Derivatives, Fair Value
Notional Amount	1,955	1,955
Derivative Assets	266	393
Derivative Liabilities	27	2
Designated as Hedging Instrument | Cash Flow Hedging | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Derivative Assets	46	122
Derivative Liabilities	17	1
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swap | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Commercial and industrial
Derivatives, Fair Value
Notional Amount	8,000	8,000
Derivative Assets	0	0
Derivative Liabilities	2	1
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swap | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Commercial Mortgage and Commercial Construction
Derivatives, Fair Value
Notional Amount	4,000	4,000
Derivative Assets	0	0
Derivative Liabilities	15	0
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate floor | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Commercial and industrial
Derivatives, Fair Value
Notional Amount	3,000	3,000
Derivative Assets	46	122
Derivative Liabilities	0	0
Not Designated as Hedging Instrument
Derivatives, Fair Value
Derivative Assets	3,958	2,386
Derivative Liabilities	4,197	2,010
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes
Derivatives, Fair Value
Derivative Assets	104	147
Derivative Liabilities	216	221
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contracts related to MSR portfolio
Derivatives, Fair Value
Notional Amount	4,965	6,260
Derivative Assets	57	140
Derivative Liabilities	1	0
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	2,505	1,952
Derivative Assets	40	2
Derivative Liabilities	7	2
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Swap
Derivatives, Fair Value
Notional Amount	3,627	3,545
Derivative Assets	0	0
Derivative Liabilities	198	214
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Foreign exchange contracts
Derivatives, Fair Value
Notional Amount	187	158
Derivative Assets	0	0
Derivative Liabilities	3	1
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	7	5
Derivative Liabilities	7	4
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contracts for LIBOR transition
Derivatives, Fair Value
Notional Amount	2,372	2,372
Derivative Assets	0	0
Derivative Liabilities	0	0
Not Designated as Hedging Instrument | Customer Accommodation
Derivatives, Fair Value
Derivative Assets	3,854	2,239
Derivative Liabilities	3,981	1,789
Not Designated as Hedging Instrument | Customer Accommodation | Foreign exchange contracts
Derivatives, Fair Value
Notional Amount	22,264	23,148
Derivative Assets	367	323
Derivative Liabilities	354	297
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate contracts
Derivatives, Fair Value
Notional Amount	76,263	76,061
Derivative Assets	423	578
Derivative Liabilities	674	232
Amount of variation margin payment applied to derivative asset contracts	316	104
Amount of variation margin payment applied to derivative liability contracts	80	472
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate lock commitments
Derivatives, Fair Value
Notional Amount	773	673
Derivative Assets	8	12
Derivative Liabilities	2	0
Not Designated as Hedging Instrument | Customer Accommodation | Commodity contracts
Derivatives, Fair Value
Notional Amount	14,720	12,376
Derivative Assets	3,056	1,326
Derivative Liabilities	2,951	1,260
Not Designated as Hedging Instrument | Customer Accommodation | TBA securities
Derivatives, Fair Value
Notional Amount	48	55
Derivative Assets	0	0
Derivative Liabilities	$ 0	$ 0