Loans and Allowance for Loan Losses - Summary of Nonaccrual Loans (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	$ 534		$ 638
Troubled debt restructured loans that continue to accrue interest	364		252
Troubled debt restructured nonaccrual loans (included in the total nonaccrual loans above)	228		221
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	36		127
Commercial mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	91		139
Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans			16
Commercial portfolio [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	127		282
Residential mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	325		285
Home equity and other consumer loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	52	21	24
Consumer portfolio [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	377		309
Nonaccrual loans excluding FDIC covered loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	504		591
FDIC covered Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	$ 30		$ 47