Accumulated Other Comprehensive Income - Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012
Unrealized gains (losses) on securities available-for-sale, not other-than temporarily impaired:
Balance at beginning of period	$ 992		$ 883
Other comprehensive income for period:
Net unrealized holding losses arising during period, net of tax of ($61) million and $(75) million, respectively	(82)		(109)
Reclassification adjustment for gains realized in net income, net of tax of ($47) million and $(12) million, respectively	(68)	[1]	(18)	[1]
Total other comprehensive loss for period	(150)		(127)
Balance at end of period	842		756
Unrealized (losses) gains on derivatives classified as cash flow hedges:
Balance at beginning of period	(201)		(229)
Other comprehensive income (loss) for period:
Net gains arising during period, net of tax of $13 million and $27 million, respectively	21		35
Reclassification adjustment for losses realized in net income, net of tax of $2 million and $2 million, respectively	2	[2]	2	[2]
Total other comprehensive income for period	23		37
Balance at end of period	(178)		(192)
Pension and postretirement benefit liability:
Balance at beginning of period	(6)		(12)
Other comprehensive income (loss) for period:
Change in unfunded pension postretirement liability, net of tax of $1 million	0		1
Amortization of prior service costs and transition obligation included in net income	0	[3]	0	[3]
Total other comprehensive income for period	0		1
Balance at end of period	(6)		(11)
Total accumulated other comprehensive income at end of period	$ 658		$ 553		$ 785

[1] Amount reclassified to net income is included in other securities gains, net in our consolidated statement of income.

[2] Amount reclassified to net income relates to interest rate contracts and is included in interest income (expense) in our consolidated statement of income.

[3] Amount reclassified to net income is included in salaries and employee benefits in our consolidated statement of income.