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	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	$ 86	$ 199
Post-Modification Outstanding Recorded Investment	83	193
Commercial and industrial [Member]
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	49	125
Post-Modification Outstanding Recorded Investment	47	121
Commercial mortgage [Member]
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	4	15
Post-Modification Outstanding Recorded Investment	4	15
Commercial portfolio [Member]
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	53	140
Post-Modification Outstanding Recorded Investment	51	136
Residential mortgage [Member]
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	30	55
Post-Modification Outstanding Recorded Investment	30	54
Home equity and other consumer loans [Member]
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	3	4
Post-Modification Outstanding Recorded Investment	2	3
Consumer portfolio [Member]
Financing Receivable, Modifications [Line Items]
Pre-Modification Outstanding Recorded Investment	33	59
Post-Modification Outstanding Recorded Investment	$ 32	$ 57