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, 2020	Dec. 31, 2019
Derivatives, Fair Value
Derivative Assets	$ 2,919	$ 1,673
Derivative Liabilities	1,072	741
Amount of variation margin payment applied to derivative asset contracts	1,100	623
Amount of variation margin payment applied to derivative liability contracts	1,100	488
Designated as Hedging Instrument | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Derivative Assets	788	508
Derivative Liabilities	2	2
Designated as Hedging Instrument | Fair Value Hedging | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Derivative Assets	528	393
Derivative Liabilities	0	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	2,705
Derivative Assets	528	393
Derivative Liabilities	0	0
Designated as Hedging Instrument | Cash Flow Hedging | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Derivative Assets	260	115
Derivative Liabilities	2	2
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swap | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Commercial and industrial loans
Derivatives, Fair Value
Notional Amount	8,000	8,000
Derivative Assets	16	0
Derivative Liabilities	2	2
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate floor | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Commercial and industrial loans
Derivatives, Fair Value
Notional Amount	3,000	3,000
Derivative Assets	244	115
Derivative Liabilities	0	0
Not Designated as Hedging Instrument
Derivatives, Fair Value
Derivative Assets	2,131	1,165
Derivative Liabilities	1,070	739
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes
Derivatives, Fair Value
Derivative Assets	206	132
Derivative Liabilities	222	175
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contract | Servicing rights
Derivatives, Fair Value
Notional Amount	6,910	6,420
Derivative Assets	202	131
Derivative Liabilities	1	2
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contracts for collateral management
Derivatives, Fair Value
Notional Amount	12,000
Derivative Assets	3
Derivative Liabilities	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
Derivative Assets	0
Derivative Liabilities	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	2,903	2,901
Derivative Assets	1	1
Derivative Liabilities	16	5
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Swap
Derivatives, Fair Value
Notional Amount	3,588	3,082
Derivative Assets	0	0
Derivative Liabilities	201	163
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Foreign exchange contracts
Derivatives, Fair Value
Notional Amount	204	195
Derivative Assets	0	0
Derivative Liabilities	3	5
Not Designated as Hedging Instrument | Customer Accommodation
Derivatives, Fair Value
Derivative Assets	1,925	1,033
Derivative Liabilities	848	564
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate contract
Derivatives, Fair Value
Notional Amount	77,806	73,327
Derivative Assets	1,238	579
Derivative Liabilities	265	148
Amount of variation margin payment applied to derivative asset contracts	47	40
Amount of variation margin payment applied to derivative liability contracts	1,063	493
Not Designated as Hedging Instrument | Customer Accommodation | Foreign exchange contracts
Derivatives, Fair Value
Notional Amount	14,587	14,144
Derivative Assets	255	165
Derivative Liabilities	224	146
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate lock commitments
Derivatives, Fair Value
Notional Amount	1,830	907
Derivative Assets	57	18
Derivative Liabilities	0	0
Not Designated as Hedging Instrument | Customer Accommodation | Commodity contracts
Derivatives, Fair Value
Notional Amount	7,762	8,525
Derivative Assets	375	271
Derivative Liabilities	$ 359	270
Not Designated as Hedging Instrument | Customer Accommodation | TBA securities
Derivatives, Fair Value
Notional Amount		50
Derivative Assets		0
Derivative Liabilities		$ 0