Asset Quality - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015 SecurityLoan	Mar. 31, 2014 SecurityLoan	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Estimated gross contractual amount receivable of PCI loans	$ 41
Estimated cash flows nonaccretable amount	11
Estimated cash flows accretable amount	5
Purchased Credit Impaired, Outstanding	12	16	13
Changes in the accretable yield, accretion	1
Changes in the accretable yield, net reclassifications	1
Accretable yield	5
Percentage of carrying amount of our commercial nonperforming loans outstanding	79.00%
Percentage of nonperforming loans outstanding face value	81.00%
Percentage of loans held for sale and other nonperforming assets	81.00%
Aggregate carrying amount of largest nonperforming loans		75
Number of largest nonperforming loans	20	20
Total loans on nonperforming status from continuing operations	123
Percentage of total loans on nonperforming status	28.00%	17.00%
Net reduction to interest income	4		16
Interest income recognized on outstanding balances	1	2
Total restructured loans	268	294	270
Addition in restructured loans	11
Restructured loans partially in payments and charge-offs	13
loans net of deferred income	57,953	55,445	57,381
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
Number of days to designate the charge-off policy for credit card loans taking effect, payment due period	180 days
ALLL	794	834	794
ALLL percentage	1.37%	1.50%
ALLL of nonperforming loans percentage	181.70%	185.70%
Increase (decrease) in allowance for loan losses	(40)
Percentage decrease in allowance for loan losses	4.80%
Individually evaluated for impairment, outstanding	338	304	302
Individually evaluated for Impairment, corresponding allowance	49	34	40
Collectively Evaluated for Impairment, Outstanding	57,603	55,125	57,066
Collectively evaluated for current, corresponding allowance	744	799	753
Provision (credit) for loan and lease losses	6	2
Liability for credit losses on lending-related commitments	41	35	35	37
Percentage of total allowance for credit losses	1.44%	1.57%
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Outstanding		1	1
Nature of default in repayment of loan TDRs	90 days past due
Number of loans		2
Financial receivable, modifications, subsequent default, recorded investment		11
loans net of deferred income	42,151	39,504	41,381
Individually evaluated for impairment, outstanding	109	71	72
Individually evaluated for Impairment, corresponding allowance	22	3	12
Collectively Evaluated for Impairment, Outstanding	42,042	39,432	41,308
Collectively evaluated for current, corresponding allowance	614	630	611
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Outstanding	12	15	12
Nature of default in repayment of loan TDRs	More than 60 days past due
Number of loans	89	157
Financial receivable, modifications, subsequent default, recorded investment	4	4
loans net of deferred income	15,802	15,941	16,000
Individually evaluated for impairment, outstanding	229	233	230
Individually evaluated for Impairment, corresponding allowance	27	31	28
Collectively Evaluated for Impairment, Outstanding	15,561	15,693	15,758
Collectively evaluated for current, corresponding allowance	130	169	142
Purchase Credit Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for Impairment, corresponding allowance	1	1
Collectively Evaluated for Impairment, Outstanding	12	16
Provision (credit) for loan and lease losses	0	0
Performing [Member] | Loans, Total [Member] | Credit Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
loans net of deferred income	57,200
Concentration risk	98.70%
Nonperforming [Member] | Loans, Total [Member] | Credit Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
loans net of deferred income	764
Concentration risk	1.30%
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Outstanding	19
Purchased credit impaired loans carrying value	$ 12