Derivative Financial Instruments - Notional Amounts and Fair Values for All Derivative Instruments Included in the Condensed Consolidated Balance Sheets (Details) - USD ($)	Sep. 30, 2020	Sep. 29, 2020	Dec. 31, 2019
Derivatives, Fair Value
Derivative Assets	$ 3,222,000,000		$ 1,673,000,000
Derivative Liabilities	1,118,000,000		741,000,000
Amount of variation margin payment applied to derivative asset contracts	1,200,000,000		623,000,000
Amount of variation margin payment applied to derivative liability contracts	1,300,000,000		488,000,000
Fair Value Hedging | Interest rate swap
Derivatives, Fair Value
Notional Amount		$ 750,000,000
Designated as Hedging Instrument | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Derivative Assets	846,000,000		508,000,000
Derivative Liabilities	1,000,000		2,000,000
Designated as Hedging Instrument | Fair Value Hedging | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Derivative Assets	581,000,000		393,000,000
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	1,955,000,000		2,705,000,000
Derivative Assets	581,000,000		393,000,000
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	265,000,000		115,000,000
Derivative Liabilities	1,000,000		2,000,000
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	8,000,000,000		8,000,000,000
Derivative Assets	0		0
Derivative Liabilities	1,000,000		2,000,000
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	3,000,000,000		3,000,000,000
Derivative Assets	265,000,000		115,000,000
Derivative Liabilities	0		0
Not Designated as Hedging Instrument
Derivatives, Fair Value
Derivative Assets	2,376,000,000		1,165,000,000
Derivative Liabilities	1,117,000,000		739,000,000
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes
Derivatives, Fair Value
Derivative Assets	233,000,000		132,000,000
Derivative Liabilities	200,000,000		175,000,000
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate swap
Derivatives, Fair Value
Notional Amount	750,000,000
Derivative Assets	0
Derivative Liabilities	0
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contracts
Derivatives, Fair Value
Notional Amount	12,000,000,000
Derivative Assets	1,000,000
Derivative Liabilities	1,000,000
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Interest rate contracts | MSR portfolio
Derivatives, Fair Value
Notional Amount	6,560,000,000		6,420,000,000
Derivative Assets	227,000,000		131,000,000
Derivative Liabilities	1,000,000		2,000,000
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	3,087,000,000		2,901,000,000
Derivative Assets	2,000,000		1,000,000
Derivative Liabilities	10,000,000		5,000,000
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Swap
Derivatives, Fair Value
Notional Amount	3,280,000,000		3,082,000,000
Derivative Assets	0		0
Derivative Liabilities	188,000,000		163,000,000
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Foreign exchange contracts
Derivatives, Fair Value
Notional Amount	169,000,000		195,000,000
Derivative Assets	3,000,000		0
Derivative Liabilities	0		5,000,000
Not Designated as Hedging Instrument | Risk Management and Other Business Purposes | Commercial loan trading
Derivatives, Fair Value
Notional Amount	6,000,000
Derivative Assets	0
Derivative Liabilities	0
Not Designated as Hedging Instrument | Customer Accommodation
Derivatives, Fair Value
Derivative Assets	2,143,000,000		1,033,000,000
Derivative Liabilities	917,000,000		564,000,000
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate contracts
Derivatives, Fair Value
Notional Amount	79,286,000,000		73,327,000,000
Derivative Assets	1,399,000,000		579,000,000
Derivative Liabilities	293,000,000		148,000,000
Amount of variation margin payment applied to derivative asset contracts	50,000,000		40,000,000
Amount of variation margin payment applied to derivative liability contracts	1,211,000,000		493,000,000
Not Designated as Hedging Instrument | Customer Accommodation | Foreign exchange contracts
Derivatives, Fair Value
Notional Amount	13,154,000,000		14,144,000,000
Derivative Assets	176,000,000		165,000,000
Derivative Liabilities	136,000,000		146,000,000
Not Designated as Hedging Instrument | Customer Accommodation | Interest rate lock commitments
Derivatives, Fair Value
Notional Amount	3,044,000,000		907,000,000
Derivative Assets	85,000,000		18,000,000
Derivative Liabilities	0		0
Not Designated as Hedging Instrument | Customer Accommodation | Commodity contracts
Derivatives, Fair Value
Notional Amount	7,441,000,000		8,525,000,000
Derivative Assets	483,000,000		271,000,000
Derivative Liabilities	488,000,000		270,000,000
Not Designated as Hedging Instrument | Customer Accommodation | TBA securities
Derivatives, Fair Value
Notional Amount	67,000,000		50,000,000
Derivative Assets	0		0
Derivative Liabilities	$ 0		$ 0