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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
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	$ 2	$ (2)	$ 2	$ (8)
Customer-Related Positions [Member] | Interest Rate Contracts [Member] | Commercial Products Revenue [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	(351)	(323)	(1,515)	(573)
Customer-Related Positions [Member] | Interest Rate Contracts [Member] | Commercial Products Revenue [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	365	333	1,532	602
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	3		11	(2)
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	22	24	45	46
Customer-Related Positions [Member] | Foreign Exchange Option [Member] | Commercial Products Revenue [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings				1
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Mortgage Banking Revenue [Member] | Futures and Forwards [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	15	(1)	73	5
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	56	77	98	117
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Mortgage Banking Revenue [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	(61)	117	(140)	148
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Mortgage Banking Revenue [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	15	(71)	(16)	(111)
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	15	(30)	27	(37)
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)
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Credit Contracts [Member] | Other Noninterest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings	2		2	1
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	$ (1)