Asset Quality - Additional Information (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($) SecurityLoan	Sep. 30, 2014 USD ($) SecurityLoan	Sep. 30, 2015 USD ($) SecurityLoan	Sep. 30, 2014 USD ($) SecurityLoan	Dec. 31, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2013 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Estimated gross contractual amount receivable of PCI loans	$ 41,000,000		$ 41,000,000
Estimated cash flows nonaccretable amount			11,000,000
Estimated cash flows accretable amount	5,000,000		5,000,000
Purchased Credit Impaired, Outstanding	12,000,000	$ 14,000,000	12,000,000	$ 14,000,000	$ 13,000,000
Accretable yield	$ 5,000,000		$ 5,000,000
Percentage of carrying amount of our commercial nonperforming loans outstanding	74.00%		74.00%
Percentage of nonperforming loans outstanding face value	79.00%		79.00%
Percentage of loans held for sale and other nonperforming assets	79.00%		79.00%
Aggregate carrying amount of largest nonperforming loans	$ 112,000,000	$ 72,000,000	$ 112,000,000	$ 72,000,000
Number of largest nonperforming loans | SecurityLoan	20	20	20	20
Percentage of total loans on nonperforming status	28.00%	18.00%	28.00%	18.00%
Net reduction to interest income			$ 12,000,000		16,000,000
Interest income recognized on outstanding balances			5,000,000	$ 5,000,000
Total restructured loans	$ 287,000,000	$ 264,000,000	287,000,000	264,000,000	270,000,000
Addition in restructured loans			87,000,000
Restructured loans partially in payments and charge-offs			70,000,000
Loans net of deferred income	60,085,000,000	56,155,000,000	60,085,000,000	56,155,000,000	57,381,000,000
Minimum outstanding impaired commercial loans	2,500,000		$ 2,500,000
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 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 net realizable value 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	790,000,000	804,000,000	$ 790,000,000	$ 804,000,000	794,000,000
ALLL percentage			1.31%	1.43%
ALLL of nonperforming loans percentage			197.50%	200.50%
Provision (credit) for loan and lease losses			$ 110,000,000	$ 52,000,000
Liability for credit losses on lending-related commitments	$ 54,000,000	$ 35,000,000	$ 54,000,000	$ 35,000,000	35,000,000	$ 45,000,000	$ 37,000,000	$ 37,000,000
Percentage of total allowance for credit losses	1.40%	1.49%	1.40%	1.49%
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Changes in the accretable yield, accretion			$ 1,000,000
Changes in the accretable yield, net reclassifications			$ 1,000,000
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nature of default in repayment of loan TDRs			90 days past due
Number of loans | SecurityLoan	0	0
Loans net of deferred income	$ 44,274,000,000	$ 40,130,000,000	$ 44,274,000,000	$ 40,130,000,000	41,381,000,000
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nature of default in repayment of loan TDRs			More than 60 days past due
Number of loans | SecurityLoan	61	93
Financial receivable, modifications, subsequent default, recorded investment	$ 3,000,000	$ 4,000,000
Loans net of deferred income	15,811,000,000	16,025,000,000	$ 15,811,000,000	16,025,000,000	16,000,000,000
Continuing Operations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Outstanding	12,000,000	14,000,000	12,000,000	14,000,000	13,000,000
Loans net of deferred income	60,085,000,000	56,155,000,000	60,085,000,000	56,155,000,000	57,381,000,000
Increase (decrease) in allowance for loan losses			$ (14,000,000)
Percentage decrease in allowance for loan losses			1.70%
Individually evaluated for impairment, outstanding	318,000,000	299,000,000	$ 318,000,000	299,000,000	302,000,000
Individually evaluated for Impairment, corresponding allowance	36,000,000	38,000,000	36,000,000	38,000,000	40,000,000
Collectively Evaluated for Impairment, Outstanding	59,755,000,000	55,842,000,000	59,755,000,000	55,842,000,000	57,066,000,000
Collectively evaluated for current, corresponding allowance	753,000,000	765,000,000	753,000,000	765,000,000	753,000,000
Provision (credit) for loan and lease losses			101,000,000	37,000,000
Continuing Operations [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Outstanding	0	1,000,000	0	1,000,000	1,000,000
Loans net of deferred income	44,274,000,000	40,130,000,000	44,274,000,000	40,130,000,000	41,381,000,000
Individually evaluated for impairment, outstanding	92,000,000	70,000,000	92,000,000	70,000,000	72,000,000
Individually evaluated for Impairment, corresponding allowance	10,000,000	9,000,000	10,000,000	9,000,000	12,000,000
Collectively Evaluated for Impairment, Outstanding	44,182,000,000	40,059,000,000	44,182,000,000	40,059,000,000	41,308,000,000
Collectively evaluated for current, corresponding allowance	637,000,000	619,000,000	637,000,000	619,000,000	611,000,000
Provision (credit) for loan and lease losses			68,000,000
Continuing Operations [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Outstanding	12,000,000	13,000,000	12,000,000	13,000,000	12,000,000
Loans net of deferred income	15,811,000,000	16,025,000,000	15,811,000,000	16,025,000,000	16,000,000,000
Individually evaluated for impairment, outstanding	226,000,000	229,000,000	226,000,000	229,000,000	230,000,000
Individually evaluated for Impairment, corresponding allowance	26,000,000	29,000,000	26,000,000	29,000,000	28,000,000
Collectively Evaluated for Impairment, Outstanding	15,573,000,000	15,783,000,000	15,573,000,000	15,783,000,000	15,758,000,000
Collectively evaluated for current, corresponding allowance	116,000,000	146,000,000	116,000,000	146,000,000	142,000,000
Provision (credit) for loan and lease losses			33,000,000	37,000,000
Continuing Operations [Member] | Purchase Credit Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for Impairment, corresponding allowance	1,000,000	1,000,000	1,000,000	1,000,000
Collectively Evaluated for Impairment, Outstanding	12,000,000	14,000,000	12,000,000	14,000,000
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	59,300,000,000	55,300,000,000	$ 59,300,000,000	$ 55,300,000,000	$ 56,600,000,000
Concentration risk			98.80%	98.50%	98.70%
Nonperforming [Member] | Loans, Total [Member] | Credit Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans net of deferred income	724,000,000	$ 813,000,000	$ 724,000,000	$ 813,000,000	$ 749,000,000
Concentration risk			1.20%	1.50%	1.30%
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Outstanding	18,000,000		$ 18,000,000
Purchased credit impaired loans carrying value	$ 12,000,000		$ 12,000,000