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Carrying Amounts and Estimated Fair Values for Certain Financial Instruments (Parenthetical) (Detail) (Residential Mortgage Loans, USD $)
In Millions
Jun. 30, 2011
Dec. 31, 2010
Jun. 30, 2010
Residential Mortgage Loans
     
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Loans measured at fair value on a recurring basis $ 59 $ 46 $ 41