v2.4.0.6
Changes in Allowance for Loan Losses (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]    
Balance at beginning of period $ 56 $ 54
Charge-offs (4) (5)
Recoveries 1 1
Provision for loan losses 6  
Balance at end of period 59 50
Residential real estate mortgages
   
Financing Receivable, Allowance for Credit Losses [Line Items]    
Balance at beginning of period 36 40
Charge-offs (2) (3)
Recoveries 1 1
Provision for loan losses 5 (1)
Balance at end of period 40 37
Home equity lines of credit
   
Financing Receivable, Allowance for Credit Losses [Line Items]    
Balance at beginning of period 20 14
Charge-offs (2) (2)
Provision for loan losses 1 1
Balance at end of period $ 19 $ 13