Loans and Leases and the Allowance for Credit Losses - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Residential mortgage loans [Member]	Dec. 30, 2012 Residential mortgage loans [Member]	Sep. 30, 2013 Commercial Real Estate [Member]	Dec. 30, 2012 Commercial Real Estate [Member]
Loans And Leases Receivable [Line Items]
Contractual principal and interest payments	$ 357		$ 447
Purchased impaired loans as a percentage of total assets	Less than 1% of the Company's assets		Less than 1% of the Company's assets
Mortgage loans held for sale				667	1,200
Commercial mortgage loans held for sale						152	200
Loan delinquent period	90 days or more
Maturity period of line of credit	More than 150 days
Payment default for troubled debt restructuring	$ 20	$ 13