Loans and Allowance for Loan Losses - Pre- and Post-Modification Outstanding Recorded Investment Amounts of Troubled Debt Restructurings (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	$ 373	[1]	$ 515	[1]
Post-Modification Outstanding Recorded Investment	345	[2]	505	[2]
Commercial and industrial [Member]
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	154	[1]	220	[1]
Post-Modification Outstanding Recorded Investment	147	[2]	215	[2]
Commercial mortgage [Member]
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	22	[1]	120	[1]
Post-Modification Outstanding Recorded Investment	21	[2]	115	[2]
Construction [Member]
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	7	[1]	91	[1]
Post-Modification Outstanding Recorded Investment	7	[2]	91	[2]
Commercial portfolio [Member]
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	183	[1]	431	[1]
Post-Modification Outstanding Recorded Investment	175	[2]	421	[2]
Residential mortgage [Member]
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	159	[1]	82	[1]
Post-Modification Outstanding Recorded Investment	151	[2]	82	[2]
Home equity and other consumer loans [Member]
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	31	[1]	2	[1]
Post-Modification Outstanding Recorded Investment	19	[2]	2	[2]
Consumer portfolio [Member]
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	190	[1]	84	[1]
Post-Modification Outstanding Recorded Investment	$ 170	[2]	$ 84	[2]

[1] Represents the recorded investment in the loan immediately prior to the restructuring event.

[2] Represents the recorded investment in the loan immediately following the restructuring event. It includes the effect of paydowns that were required as part of the restructuring terms.