Loans - Summary of Receivables which were Modified and as Result Became Classified as TDR Loans (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Total	$ 555	$ 315
Commercial Loan [Member]
Financing Receivable, Impaired [Line Items]
Total	99	75
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total	78	70
Commercial Loan [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Impaired [Line Items]
Total	21	5
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Total	456	240
Weighted Average Rate Reduction on TDR Loans	2.60%	1.85%
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Total	452	235
Consumer Loans [Member] | Credit Card Receivables [Member]
Financing Receivable, Impaired [Line Items]
Total	$ 4	$ 5