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		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
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	$ 274	$ 7	$ 360	$ 215
Net Change in net derivative asset and liability unrealized gains (losses) relating to assets still held at end of period	159	(65)	131	30
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	152	88	365	353
Net Change in net derivative asset and liability unrealized gains (losses) relating to assets still held at end of period	$ 72	$ 50	$ 72	$ 50