Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance for Residential Mortgage Loans Measured at Fair Value (Detail) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010
Aggregate Fair Value Under Fair Value Option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage loans measured at fair value	$ 1,037	$ 1,938	$ 1,788
Past due loans of 90 days or more	3	5	6
Nonaccrual loans		1	1
Aggregate Unpaid Principal Balance Under Fair Value Option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage loans measured at fair value	1,002	1,913	1,702
Past due loans of 90 days or more	4	6	7
Nonaccrual loans		1	1
Fair Value Over/(Under) Unpaid Principal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage loans measured at fair value	35	25	86
Past due loans of 90 days or more	$ (1)	$ (1)	$ (1)