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		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Financing Receivable, Impaired [Line Items]
Total	$ 260	$ 85	$ 458	$ 240
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Total	39	27	127	46
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total	38	27	105	40
Commercial Loans [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Impaired [Line Items]
Total	1		22	6
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Total	221	58	331	194
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Total	220	56	328	189
Consumer Loans [Member] | Credit Card Receivables [Member]
Financing Receivable, Impaired [Line Items]
Total	$ 1	$ 2	$ 3	$ 5