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, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 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	$ (122)	$ 127	$ 86	$ 208
Net Change in net derivative asset and liability unrealized gains (losses) relating to assets still held at end of period	(184)	47	(60)	85
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	50	161	213	265
Net Change in net derivative asset and liability unrealized gains (losses) relating to assets still held at end of period	$ 53	$ 76	$ 54	$ 76