Loans and Allowance for Credit Losses - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2014 MortgageLoan	Sep. 30, 2014 MortgageLoan	Jun. 30, 2014	Dec. 31, 2013
Loans and Allowance for Credit Losses [Line Items]
Loans pledged at the Federal Home Loan Bank ("FHLB")	$ 79,400,000,000	$ 79,400,000,000		$ 77,200,000,000
Loans pledged at the Federal Reserve Bank	61,800,000,000	61,800,000,000		53,000,000,000
Unearned interest and deferred fees and costs on loans	575,000,000	575,000,000		556,000,000
Contractually required payments receivable for all purchased nonimpaired loans acquired in the Charter One acquisition			1,500,000,000
Contractual cash flows not expected to be collected in the Charter One acquisition			247,000,000
Fair value of loans acquired in the Charter One acquisition			969,000,000
Purchased impaired loans acquired in the Charter One acquisition			0
Minimum period for non collection of principal and interest placed on nonaccrual status for commercial lending segment loans		90 days
Minimum period beyond which revolving consumer lines and credit cards are charged off		180 days
Minimum period beyond which residential mortgages and other retail loans secured by 1-4 family properties are charged down to fair value of the collateral securing the loan less costs to sell		180 days
Minimum period beyond which other retail loans not secured by 1-4 family properties are charged off		120 days
Foreclosed residential real estate property included in other real estate owned	273,000,000	273,000,000
Foreclosed residential real estate property included in other real estate owned excluding covered assets	236,000,000	236,000,000
Foreclosed residential real estate related to mortgage loans whose payments are insured by the Federal Housing Administration or guaranteed by the Department of Veterans Affairs	623,000,000	623,000,000
Residential mortgage loans secured by residential real estate in process of foreclosure	3,000,000,000	3,000,000,000
Maximum restructuring period under credit card and other retail loan financial difficulty modifications		60 months
Number of residential mortgage loans, home equity and second mortgage loans, and GNMA loans where trial period arrangement was unsuccessful and no longer eligible for a permanent modification	435	1,313
Outstanding balance of residential mortgage loans, home equity and second mortgage loans, and GNMA loans where trial period was unsuccessful and no longer eligible for a permanent modification	57,000,000	159,000,000
Remaining term for single family residential mortgages covered under loss sharing agreements		5 years
Purchased impaired loans included in covered loans classified as nonperforming assets	5,000,000	5,000,000		5,000,000
Commercial Lending Segment [Member] | Maximum [Member]
Loans and Allowance for Credit Losses [Line Items]
Period of loss experience		13 years
Commercial Lending Segment [Member] | Minimum [Member]
Loans and Allowance for Credit Losses [Line Items]
Impairment loan threshold for allowance in which loans are individually analyzed	5,000,000	5,000,000
Junior Lien [Member]
Loans and Allowance for Credit Losses [Line Items]
Loans and lines in a junior lien position secured by 1-4 family properties placed on nonaccrual status		120 days
First Lien [Member]
Loans and Allowance for Credit Losses [Line Items]
Loans and lines in a junior lien position placed on nonaccrual status when behind a first lien past due		180 days
Government National Mortgage Association [Member]
Loans and Allowance for Credit Losses [Line Items]
Residential mortgage loans secured by residential real estate in process of foreclosure purchased from Government National Mortgage Association mortgage pools whose repayments are insured by the Federal Housing Administration or guaranteed by the Department of Veterans Affairs	2,100,000,000	2,100,000,000
Residential Mortgages [Member]
Loans and Allowance for Credit Losses [Line Items]
Number of loans in trial period	310	310
Outstanding balance of loans in trial period	40,000,000	40,000,000
Estimated post-modification balance of loans in trial period	41,000,000	41,000,000
Home equity and second mortgage loans [Member]
Loans and Allowance for Credit Losses [Line Items]
Number of loans in trial period	49	49
Outstanding balance of loans in trial period	3,000,000	3,000,000
Estimated post-modification balance of loans in trial period	3,000,000	3,000,000
Loans Purchased from GNMA Mortgage Pools [Member]
Loans and Allowance for Credit Losses [Line Items]
Number of loans in trial period	1,764	1,764
Outstanding balance of loans in trial period	231,000,000	231,000,000
Estimated post-modification balance of loans in trial period	$ 232,000,000	$ 232,000,000