Summary of Loans Modified in a TDR (Parenthetical) (Detail) (Commercial Portfolio Segment, Commercial Mortgage Loans, Owner Occupied, Consolidated Variable Interest Entity, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner Occupied | Consolidated Variable Interest Entity
Financing Receivable, Modifications
Financing Receivable, Modifications, Number of Contracts	5
Financing Receivable Modifications Post Modification Recorded Investment	$ 29
Allowance for Loan and Lease Losses, Adjustments, Net	7
Allowance for Loan and Lease Losses, Write-offs	$ 2