Derivative Financial Instruments - Notional Amounts and Fair Values for All Derivative Instruments Included in the Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Derivatives, Fair Value
Derivative assets, fair value, gross assets	$ 2,896	$ 2,862
Total derivative assets	2,908	2,919
Derivative liabilities, fair value, gross liabilities	2,013	1,072
Total derivative liabilities	2,013	1,072
Amount of variation margin payment applied to derivative asset contracts	771	1,100
Amount of variation margin payment applied to derivative liability contracts	570	1,100
Designated as Hedging Instrument | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Derivative assets, fair value, gross assets	522	788
Derivative liabilities, fair value, gross liabilities	3	2
Designated as Hedging Instrument | Fair Value Hedging | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Derivative assets, fair value, gross assets	400	528
Derivative liabilities, fair value, gross liabilities	2	0
Designated as Hedging Instrument | Fair Value Hedging | Interest rate swaps | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Available-for-sale debt and other securities
Derivatives, Fair Value
Notional Amount	445
Derivative assets, fair value, gross assets	7
Derivative liabilities, fair value, gross liabilities	0
Designated as Hedging Instrument | Fair Value Hedging | Interest rate swaps | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Long-term debt
Derivatives, Fair Value
Notional Amount	1,955	1,955
Derivative assets, fair value, gross assets	393	528
Derivative liabilities, fair value, gross liabilities	2	0
Designated as Hedging Instrument | Cash Flow Hedging | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Derivative assets, fair value, gross assets	122	260
Derivative liabilities, fair value, gross liabilities	1	2
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swaps | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Commercial and Industrial
Derivatives, Fair Value
Notional Amount	8,000	8,000
Derivative assets, fair value, gross assets	0	16
Derivative liabilities, fair value, gross liabilities	1	2
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swaps | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Commercial Mortgage and Commercial Construction
Derivatives, Fair Value
Notional Amount	4,000
Derivative assets, fair value, gross assets	0
Derivative liabilities, fair value, gross liabilities	0
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate floors | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Commercial and Industrial
Derivatives, Fair Value
Notional Amount	3,000	3,000
Derivative assets, fair value, gross assets	122	244
Derivative liabilities, fair value, gross liabilities	0	0
Not Designated as Hedging Instrument
Derivatives, Fair Value
Total derivative assets	2,386	2,131
Total derivative liabilities	2,010	1,070
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes
Derivatives, Fair Value
Derivative assets, fair value, gross assets	147	206
Derivative liabilities, fair value, gross liabilities	221	222
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contracts related to MSR portfolio
Derivatives, Fair Value
Notional Amount	6,260	6,910
Derivative assets, fair value, gross assets	140	202
Derivative liabilities, fair value, gross liabilities	0	1
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	1,952	2,903
Derivative assets, fair value, gross assets	2	1
Derivative liabilities, fair value, gross liabilities	2	16
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Swap
Derivatives, Fair Value
Notional Amount	3,545	3,588
Derivative assets, fair value, gross assets	0	0
Derivative liabilities, fair value, gross liabilities	214	201
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Foreign exchange contracts
Derivatives, Fair Value
Notional Amount	158	204
Derivative assets, fair value, gross assets	0	0
Derivative liabilities, fair value, gross liabilities	1	3
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, fair value, gross assets	5	3
Derivative liabilities, fair value, gross liabilities	4	1
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, fair value, gross assets	0	0
Derivative liabilities, fair value, gross liabilities	0	0
Not Designated as Hedging Instrument | Customer Accommodation
Derivatives, Fair Value
Total derivative assets	2,239	1,925
Total derivative liabilities	1,789	848
Not Designated as Hedging Instrument | Customer Accommodation | Foreign exchange contracts
Derivatives, Fair Value
Notional Amount	23,148	14,587
Derivative assets, fair value, gross assets	323	255
Derivative liabilities, fair value, gross liabilities	297	224
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate contracts
Derivatives, Fair Value
Notional Amount	76,061	77,806
Derivative assets, fair value, gross assets	578	1,238
Derivative liabilities, fair value, gross liabilities	232	265
Amount of variation margin payment applied to derivative asset contracts	104	47
Amount of variation margin payment applied to derivative liability contracts	472	1,063
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate lock commitments
Derivatives, Fair Value
Notional Amount	673	1,830
Derivative assets, not subject to master netting arrangement	12	57
Derivative liabilities, not subject to master netting arrangement	0	0
Not Designated as Hedging Instrument | Customer Accommodation | Commodity contracts
Derivatives, Fair Value
Notional Amount	12,376	7,762
Derivative assets, fair value, gross assets	1,326	375
Derivative liabilities, fair value, gross liabilities	1,260	$ 359
Not Designated as Hedging Instrument | Customer Accommodation | TBA securities
Derivatives, Fair Value
Notional Amount	55
Derivative assets, fair value, gross assets	0
Derivative liabilities, fair value, gross liabilities	$ 0