Fair Values of Assets and Liabilities - Changes in Fair Value for All Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3) (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Other Noninterest Income [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net gains and (losses) on net derivative assets and liabilities included in net income		$ (1)	$ (1)
Net Change in net derivative asset and liability unrealized gains (losses) relating to assets still held at end of period		(1)	(1)
Mortgage Banking Revenue [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net gains and (losses) on net derivative assets and liabilities included in net income	$ 622	136	979	$ 219
Net Change in net derivative asset and liability unrealized gains (losses) relating to assets still held at end of period	334	51	334	52
Commercial Products Revenue [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net gains and (losses) on net derivative assets and liabilities included in net income	110	433	1,500	712
Net Change in net derivative asset and liability unrealized gains (losses) relating to assets still held at end of period	$ 306	$ 612	$ 1,700	$ 967