Asset Quality - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013 SecurityLoan	Mar. 31, 2012 SecurityLoan	Dec. 31, 2012	Dec. 31, 2011
Estimated gross contractual amount receivable of PCI loans	$ 41
Estimated cash flows nonaccretable amount	11
Estimated cash flows accretable amount	5
Purchased credit impaired loans	22		23
Changes in the accretable yield, net reclassifications	1
Accretable yield	4
Percentage of carrying amount of our commercial nonperforming loans outstanding	63.00%
Percentage of nonperforming loans outstanding face value	76.00%
Percentage of loans held for sale and other nonperforming assets	73.00%
Aggregate carrying amount of largest nonperforming loans	194
Number of largest nonperforming loans	20	20
Total loans on nonperforming status from continuing operations		215
Percentage of total loans on nonperforming status	30.00%	32.00%
Net reduction to interest income	6		25
Interest income recognized on outstanding balances	2	1
Total restructured loans	294	293	320
Addition in restructured loans	34
Restructured loans partially in payments and charge-offs	60
Total current loan	51,451	47,971	51,623
Percent of total current loan	97.90%
Total past due loan	1,101	1,255	1,176
Percent of total past due loans	2.10%
Minimum outstanding impaired commercial loans	2.5
Number of days to designate commercial loans will be charged off in full or charged down to the fair value of the underlying collateral payment due period	180 days
Number of days to designate the charge-off policy for most consumer loans taking effect, payment due period	120 days
Number of days to designate home equity and residential mortgage loans to get charged down to the fair value of the underlying collateral payment due period	180 days
ALLL	893	944	888
ALLL percentage	1.70%	1.92%
ALLL of nonperforming loans percentage	137.38%	141.74%
Increase (decrease) in allowance for loan losses	51
Percentage decrease in allowance for loan losses	5.00%
Individually evaluated for impairment, corresponding allowance	445	359	411
Corresponding allowance	34	38	35
Collectively Evaluated for Impairment, Outstanding	52,107	48,867	52,388
Collectively evaluated for current, corresponding allowance	859
Increase decrease liability for credit losses on lending related commitments		13
Percentage of total allowance for credit losses	1.76%	2.01%
Liability for credit losses on lending-related commitments	32	45	29	45
PCI Loans [Member]
Purchased credit impaired loans	29
Purchased credit impaired loans carrying value	22
Consumer loans [Member]
Purchased credit impaired loans	19		19
Number of loans	240
Financial Receivable, Modifications, Subsequent Default, Recorded Investment	14
Individually evaluated for impairment, corresponding allowance	193		202
Corresponding allowance	23		22
Collectively Evaluated for Impairment, Outstanding	15,553	14,604	15,721
Purchase Credit Impaired Loans [Member]
Corresponding allowance	1
Collectively Evaluated for Impairment, Outstanding	$ 22