Loans - Summary of Receivables which were Modified and as Result Became Classified as TDR Loans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Financing Receivable, Impaired [Line Items]
Total	$ 48	$ 151
Commercial Loan [Member]
Financing Receivable, Impaired [Line Items]
Total	4	95
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total	0	73
Commercial Loan [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Impaired [Line Items]
Total	4	22
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Total	44	56
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Total	44	55
Consumer Loans [Member] | Credit Card Receivables [Member]
Financing Receivable, Impaired [Line Items]
Total	$ 0	$ 1