Summary of Subsequent Defaults (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012
Financing Receivable, Modifications [Line Items]
Number of contracts	$ 127
Recorded Investment Post Modification	17
Commercial Portfolio Segment | Commercial Mortgage Loans Non Owner Occupied [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1
Recorded Investment Post Modification	1
Commercial Portfolio Segment | Commercial Construction
Financing Receivable, Modifications [Line Items]
Number of contracts	2
Recorded Investment Post Modification	3
Consumer Portfolio Segment | Home Equity
Financing Receivable, Modifications [Line Items]
Number of contracts	31
Recorded Investment Post Modification	2
Consumer Portfolio Segment | Automobile Loans
Financing Receivable, Modifications [Line Items]
Number of contracts	12
Consumer Portfolio Segment | Credit Card
Financing Receivable, Modifications [Line Items]
Number of contracts	17
Residential Mortgage Loans
Financing Receivable, Modifications [Line Items]
Number of contracts	64
Recorded Investment Post Modification	$ 11