Loans and Allowance for Loan Losses - Reconciliation of Changes in Allowance for Loan Losses by Portfolio Segments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning of period	$ 656	$ 826	$ 764	$ 1,191
(Reversal of) provision for loan losses	43	(13)	31	(207)
(Reversal of) provision for FDIC covered loan losses not subject to FDIC indemnification	2		(1)	(2)
Increase/Decrease in allowance covered by FDIC indemnification	8		(1)	(5)
Other	1	(1)	1	(1)
Loans charged off	57	57	164	253
Recoveries of loans previously charged off	15	13	38	45
Allowance for loan losses, end of period	668	768	668	768
FDIC Covered [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	4	17	17	25
(Reversal of) provision for FDIC covered loan losses not subject to FDIC indemnification	2		(1)	(2)
Increase/Decrease in allowance covered by FDIC indemnification	8		(1)	(5)
Other
Loans charged off	3	1	5	2
Recoveries of loans previously charged off	1	1	2	1
Loans and Leases Receivable, Allowance, Ending Balance	12	17	12	17
Commercial portfolio [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning of period	388	475	474	683
(Reversal of) provision for loan losses	(17)	30	(58)	(62)
Other	1	(1)	1	(1)
Loans charged off	13	35	79	182
Recoveries of loans previously charged off	13	10	34	41
Allowance for loan losses, end of period	372	479	372	479
Consumer portfolio [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning of period	126	151	138	185
(Reversal of) provision for loan losses	30	13	56	26
Loans charged off	41	21	80	69
Recoveries of loans previously charged off	1	2	2	3
Allowance for loan losses, end of period	116	145	116	145
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, beginning of period	138	183	135	298
(Reversal of) provision for loan losses	30	(56)	33	(171)
Allowance for loan losses, end of period	$ 168	$ 127	$ 168	$ 127