Loans and Allowance for Loan Losses - Recorded Investment Amounts of Troubled Debt Restructurings (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013
Financing Receivable, Modifications [Line Items]
Total troubled debt restructured loans at date of default	$ 11	$ 18
Commercial and industrial [Member]
Financing Receivable, Modifications [Line Items]
Total troubled debt restructured loans at date of default	3	8
Residential mortgage [Member]
Financing Receivable, Modifications [Line Items]
Total troubled debt restructured loans at date of default	7	9
Home equity and other consumer loans [Member]
Financing Receivable, Modifications [Line Items]
Total troubled debt restructured loans at date of default	1	1
Consumer portfolio [Member]
Financing Receivable, Modifications [Line Items]
Total troubled debt restructured loans at date of default	$ 8	$ 10