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, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
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	$ 7	$ 89	$ 215	$ (122)
Net Change in net derivative asset and liability unrealized gains (losses) relating to assets still held at end of period	(65)	(28)	30	(301)
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	88	93	353	88
Net Change in net derivative asset and liability unrealized gains (losses) relating to assets still held at end of period	50	83	50	83
Securities Gains Losses [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net gains and losses on available for sale securities included in net income		(3)		(13)
Interest Income [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net gains and losses on available for sale securities included in net income		$ (1)		$ (2)