Asset Quality - Additional Information (Detail)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($) SecurityLoan	Jun. 30, 2015 USD ($) SecurityLoan	Jun. 30, 2016 USD ($) SecurityLoan	Jun. 30, 2015 USD ($) SecurityLoan	Dec. 31, 2015 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
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	11,000,000	$ 12,000,000	11,000,000	$ 12,000,000	11,000,000
Accretable yield	$ 5,000,000	5,000,000	$ 5,000,000	5,000,000	5,000,000
Percentage of carrying amount of our commercial nonperforming loans outstanding	0.83%		0.83%
Percentage of nonperforming loans outstanding face value	0.83%		0.83%
Percentage of loans held for sale and other nonperforming assets	0.83%		0.83%
Aggregate carrying amount of largest nonperforming loans	$ 331,000,000	$ 120,000,000	$ 331,000,000	$ 120,000,000
Number of largest nonperforming loans | SecurityLoan	20	20	20	20
Percentage of total loans on nonperforming status	54.00%	29.00%	54.00%	29.00%
Net reduction to interest income			$ 12,000,000	$ 8,000,000
Interest income recognized on outstanding balances			6,000,000	3,000,000
Total restructured loans	$ 277,000,000	$ 300,000,000	277,000,000	300,000,000	280,000,000
Addition in restructured loans			49,000,000	73,000,000	99,000,000
Restructured loans partially in payments and charge-offs			52,000,000	43,000,000	89,000,000
Loans net of deferred income	62,098,000,000	58,264,000,000	62,098,000,000	58,264,000,000	59,876,000,000
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	854,000,000	796,000,000	$ 854,000,000	$ 796,000,000	796,000,000
ALLL percentage			1.38%	1.37%
ALLL of nonperforming loans percentage			138.00%	190.00%
Provision (credit) for loan and lease losses			$ 149,000,000	$ 67,000,000
Liability for credit losses on lending-related commitments	$ 50,000,000	$ 45,000,000	$ 50,000,000	$ 45,000,000	56,000,000	$ 69,000,000	$ 41,000,000	$ 35,000,000
Percentage of total allowance for credit losses	1.46%	1.44%	1.46%	1.44%
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Changes in the accretable yield, accretion			$ 1,000,000	$ 1,000,000	1,000,000
Changes in the accretable yield, net reclassifications			5,000,000	1,000,000	1,000,000
Continuing Operations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Outstanding	$ 11,000,000	$ 12,000,000	11,000,000	12,000,000	11,000,000
Loans net of deferred income	62,098,000,000	58,264,000,000	62,098,000,000	58,264,000,000	59,876,000,000
Increase (decrease) in allowance for loan losses				$ 58,000,000
Percentage of Increase (decrease) in allowance for loan losses				7.30%
Individually Evaluated for Impairment, Outstanding	571,000,000	334,000,000	571,000,000	$ 334,000,000	308,000,000
Individually evaluated for Impairment, corresponding allowance	41,000,000	52,000,000	41,000,000	52,000,000	35,000,000
Collectively Evaluated for Impairment, Outstanding	61,516,000,000	57,918,000,000	61,516,000,000	57,918,000,000	59,557,000,000
Collectively evaluated for Impairment, corresponding allowance	812,000,000	743,000,000	812,000,000	743,000,000	760,000,000
Provision (credit) for loan and lease losses			147,000,000	66,000,000
Continuing Operations [Member] | Purchase Credit Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively Evaluated for Impairment, Outstanding	11,000,000	12,000,000	11,000,000	12,000,000
Collectively evaluated for Impairment, corresponding allowance	$ 1,000,000	1,000,000	1,000,000	1,000,000
Provision (credit) for loan and lease losses			$ 0	0
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
Loans net of deferred income	$ 46,827,000,000	42,423,000,000	$ 46,827,000,000	42,423,000,000	44,272,000,000
Commercial Loans [Member] | Continuing Operations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans net of deferred income	46,827,000,000	42,423,000,000	46,827,000,000	42,423,000,000	44,272,000,000
Increase (decrease) in allowance for loan losses				$ 64,000,000
Percentage of Increase (decrease) in allowance for loan losses				9.90%
Individually Evaluated for Impairment, Outstanding	348,000,000	105,000,000	348,000,000	$ 105,000,000	83,000,000
Individually evaluated for Impairment, corresponding allowance	16,000,000	25,000,000	16,000,000	25,000,000	8,000,000
Collectively Evaluated for Impairment, Outstanding	46,479,000,000	42,318,000,000	46,479,000,000	42,318,000,000	44,189,000,000
Collectively evaluated for Impairment, corresponding allowance	$ 694,000,000	$ 621,000,000	694,000,000	621,000,000	648,000,000
Provision (credit) for loan and lease losses			$ 107,000,000	43,000,000
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	41	65
Financial receivable, modifications, subsequent default, recorded investment	$ 2,000,000	$ 3,000,000
Loans net of deferred income	15,271,000,000	15,841,000,000	$ 15,271,000,000	15,841,000,000	15,604,000,000
Consumer Loans [Member] | Continuing Operations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Outstanding	11,000,000	12,000,000	11,000,000	12,000,000	11,000,000
Loans net of deferred income	15,271,000,000	15,841,000,000	15,271,000,000	15,841,000,000	15,604,000,000
Increase (decrease) in allowance for loan losses				$ 6,000,000
Percentage of Increase (decrease) in allowance for loan losses				4.00%
Individually Evaluated for Impairment, Outstanding	223,000,000	229,000,000	223,000,000	$ 229,000,000	225,000,000
Individually evaluated for Impairment, corresponding allowance	25,000,000	27,000,000	25,000,000	27,000,000	27,000,000
Collectively Evaluated for Impairment, Outstanding	15,037,000,000	15,600,000,000	15,037,000,000	15,600,000,000	15,368,000,000
Collectively evaluated for Impairment, corresponding allowance	118,000,000	122,000,000	118,000,000	122,000,000	112,000,000
Provision (credit) for loan and lease losses			40,000,000	23,000,000
Performing [Member] | Loans, Total [Member] | Credit Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans net of deferred income	61,200,000,000	57,600,000,000	$ 61,200,000,000	$ 57,600,000,000	$ 59,200,000,000
Concentration risk			98.50%	98.80%	98.90%
Nonperforming [Member] | Loans, Total [Member] | Credit Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans net of deferred income	892,000,000	666,000,000	$ 892,000,000	$ 666,000,000	$ 667,000,000
Concentration risk			1.40%	1.20%	1.10%
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Outstanding	16,000,000	18,000,000	$ 16,000,000	$ 18,000,000	$ 17,000,000
Purchased credit impaired loans carrying value	$ 11,000,000	$ 12,000,000	$ 11,000,000	$ 12,000,000	$ 11,000,000