Loans - Summary of TDR and Related Credit Loss Reserves for TDR Loans (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
TDR Loans	$ 1,391	$ 1,102
Allowance for credit losses on TDR Loans	151	121
Unpaid Principal Balance of TDR Loans	1,601	1,282
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	492	473
Allowance for credit losses on TDR Loans	33	20
Unpaid Principal Balance of TDR Loans	567	580
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	375	342
Allowance for credit losses on TDR Loans	30	17
Unpaid Principal Balance of TDR Loans	407	393
Commercial Loans [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	84	94
Allowance for credit losses on TDR Loans	3	3
Unpaid Principal Balance of TDR Loans	124	147
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	33	37
Unpaid Principal Balance of TDR Loans	36	40
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	899	629
Allowance for credit losses on TDR Loans	118	101
Unpaid Principal Balance of TDR Loans	1,034	702
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	883	608
Allowance for credit losses on TDR Loans	113	94
Unpaid Principal Balance of TDR Loans	1,018	682
Consumer Loans [Member] | Credit Card Receivables [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	16	21
Allowance for credit losses on TDR Loans	5	7
Unpaid Principal Balance of TDR Loans	$ 16	$ 20