Summary of Subsequent Defaults (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 number
Financing Receivable, Modifications [Line Items]
Number of contracts	657
Recorded Investment Post Modification	$ 86
Commercial Portfolio Segment | CommercialAndIndustrialLoansMember [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	8
Recorded Investment Post Modification	4
Commercial Portfolio Segment | Commercial Mortgage Loans Owner Occupied [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4
Recorded Investment Post Modification	5
Commercial Portfolio Segment | Commercial Mortgage Loans Non Owner Occupied [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4
Recorded Investment Post Modification	3
Commercial Portfolio Segment | Commercial Construction
Financing Receivable, Modifications [Line Items]
Number of contracts	3
Recorded Investment Post Modification	4
Consumer Portfolio Segment | Home Equity
Financing Receivable, Modifications [Line Items]
Number of contracts	206
Recorded Investment Post Modification	13
Consumer Portfolio Segment | Automobile Loans
Financing Receivable, Modifications [Line Items]
Number of contracts	28
Recorded Investment Post Modification	1
Consumer Portfolio Segment | Credit Card
Financing Receivable, Modifications [Line Items]
Number of contracts	67
Recorded Investment Post Modification	1
Residential Mortgage Loans
Financing Receivable, Modifications [Line Items]
Number of contracts	337
Recorded Investment Post Modification	$ 55