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Summary of the Key Characteristics, Inputs, and Economic Assumptions Used to Estimate the Fair Value of the Company's MSRs (Detail) (Estimate of Fair Value, Fair Value Disclosure, USD $)
In Millions, unless otherwise specified
9 Months Ended12 Months Ended
Sep. 30, 2011
Dec. 31, 2010
Estimate of Fair Value, Fair Value Disclosure
  
Fair value of retained MSRs$ 1,033$ 1,439
Prepayment rate assumption (annual)18.00%12.00%
Decline in fair value from 10% adverse change7050
Decline in fair value from 20% adverse change13495
Discount rate (annual)11.00%12.00%
Decline in fair value from 10% adverse change3668
Decline in fair value from 20% adverse change$ 70$ 130
Weighted-average life (in years)4.46.2
Weighted-average coupon5.20%5.40%