Loans and Leases and the Allowance for Credit Losses - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contractual principal and interest payments	$ 237		$ 331
Purchased impaired loans as a percentage of total assets	Less than 1% of the Company's assets
Loan delinquent period	90 days
Delinquency period for loan level collectability analysis consumer mortgage	More than 150 days
Real Estate Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial mortgage loans held for sale	159		68
Troubled debt restructurings for which there was a subsequent payment default	3	20
Residential Mortgage Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans held for sale	466		401
Carrying value of loans for which partial charge-off has been recognized	64		58
Home Equity Loans And Lines of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value of loans for which partial charge-off has been recognized	$ 18		$ 18