Derivative Instruments - Summary of Gains (Losses) Recognized in Earnings for Other Economic Hedges and Customer-Related Positions (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Customer-Related Positions [Member] | Interest Rate Contracts [Member] | Commercial Products Revenue [Member] | Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	$ 4		$ (3)	$ 17
Customer-Related Positions [Member] | Interest Rate Contracts [Member] | Commercial Products Revenue [Member] | Futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings				(18)
Customer-Related Positions [Member] | Swaps [Member] | Commercial Products Revenue [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	25	$ 66	52	44
Customer-Related Positions [Member] | Credit Contracts [Member] | Commercial Products Revenue [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	(4)	(23)	(2)	(5)
Customer-Related Positions [Member] | Foreign Exchange Rate Contracts [Member] | Commercial Products Revenue [Member] | Forwards, Spots and Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	27	17	46	34
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Mortgage Banking Revenue/Other Noninterest Income [Member] | Futures and Forwards [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	(99)	82	331	7
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Mortgage Banking Revenue [Member] | Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	253	465	265	745
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Swaps [Member] | Mortgage Banking Revenue [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	193	46	(197)	775
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Foreign Exchange Forward Contracts [Member] | Other Noninterest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	(7)	(6)	(10)	11
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Equity Contracts [Member] | Compensation Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	1	$ 1	5	(3)
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Other Derivatives [Member] | Other Noninterest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	$ 1		$ 1	$ (1)