Loans and Allowance for Loan Losses - Summary of Nonaccrual Loans (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	$ 520	$ 505
Troubled debt restructured loans that continue to accrue interest	366	401
Troubled debt restructured nonaccrual loans (included in the total nonaccrual loans above)	245	209
Commercial and industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	69	48
Commercial mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	62	65
Commercial portfolio [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	131	113
Residential mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	315	306
Home equity and other consumer loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	50	56
Consumer portfolio [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	365	362
Nonaccrual loans, before purchased credit-impaired loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	496	475
Purchased Credit Impaired [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	$ 24	$ 30