Loans - Trouble Debt Restructuring Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	$ 1,274	$ 1,149
Trouble debt restructuring interest income recognized	11	9
Commercial Loan [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	411	491
Trouble debt restructuring interest income recognized	3	3
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	320	355
Trouble debt restructuring interest income recognized	2	2
Commercial Loan [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	60	100
Trouble debt restructuring interest income recognized	0	0
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	31	36
Trouble debt restructuring interest income recognized	1	1
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	863	658
Trouble debt restructuring interest income recognized	8	6
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	849	638
Trouble debt restructuring interest income recognized	8	6
Consumer Loans [Member] | Credit Card Receivables [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	14	20
Trouble debt restructuring interest income recognized	$ 0	$ 0