Derivative Financial Instruments - Notional Amounts and Fair Values for All Derivative Instruments Included in the Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value
Derivative Assets	$ 3,590	$ 1,673
Derivative Liabilities	1,294	741
Amount of variation margin payment applied to derivative asset contracts	1,200	623
Amount of variation margin payment applied to derivative liability contracts	1,400	488
Designated as Hedging Instrument | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Derivative Assets	897	508
Derivative Liabilities	4	2
Designated as Hedging Instrument | Fair Value Hedging | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Derivative Assets	616	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	2,705	2,705
Derivative Assets	616	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	281	115
Derivative Liabilities	4	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	0	0
Derivative Liabilities	4	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	281	115
Derivative Liabilities	0	0
Not Designated as Hedging Instrument
Derivatives, Fair Value
Derivative Assets	2,693	1,165
Derivative Liabilities	1,290	739
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes
Derivatives, Fair Value
Derivative Assets	294	132
Derivative Liabilities	208	175
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contracts
Derivatives, Fair Value
Notional Amount	12,000
Derivative Assets	1
Derivative Liabilities	0
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contracts | MSR portfolio
Derivatives, Fair Value
Notional Amount	6,770	6,420
Derivative Assets	289	131
Derivative Liabilities	3	2
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	4,085	2,901
Derivative Assets	4	1
Derivative Liabilities	19	5
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Swap
Derivatives, Fair Value
Notional Amount	3,169	3,082
Derivative Assets	0	0
Derivative Liabilities	183	163
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Foreign exchange contracts
Derivatives, Fair Value
Notional Amount	315	195
Derivative Assets	0	0
Derivative Liabilities	3	5
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Commercial loan trading
Derivatives, Fair Value
Notional Amount	2
Derivative Assets	0
Derivative Liabilities	0
Not Designated as Hedging Instrument | Customer Accommodation
Derivatives, Fair Value
Derivative Assets	2,399	1,033
Derivative Liabilities	1,082	564
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate contracts
Derivatives, Fair Value
Notional Amount	79,392	73,327
Derivative Assets	1,514	579
Derivative Liabilities	312	148
Amount of variation margin payment applied to derivative asset contracts	60	40
Amount of variation margin payment applied to derivative liability contracts	1,318	493
Not Designated as Hedging Instrument | Customer Accommodation | Foreign exchange contracts
Derivatives, Fair Value
Notional Amount	13,253	14,144
Derivative Assets	212	165
Derivative Liabilities	168	146
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate lock commitments
Derivatives, Fair Value
Notional Amount	2,745	907
Derivative Assets	91	18
Derivative Liabilities	0	0
Not Designated as Hedging Instrument | Customer Accommodation | Commodity contracts
Derivatives, Fair Value
Notional Amount	7,745	8,525
Derivative Assets	582	271
Derivative Liabilities	602	270
Not Designated as Hedging Instrument | Customer Accommodation | TBA securities
Derivatives, Fair Value
Notional Amount	102	50
Derivative Assets	0	0
Derivative Liabilities	$ 0	$ 0