Key economic assumptions used in measuring the servicing rights retained at the date of the residential mortgage loan securitizations and whole loan sales by the banking subsidiaries (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Assumption for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Line Items]
Assumption For Fair Value On Securitization Date Of Interests Continued To Be Held By Transferor Servicing Assets Or Liabilities Discount Rate	11.30%	11.60%	11.40%	11.50%
Residential Mortgage
Assumption for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Line Items]
Assumption For Fair Value On Securitization Date Of Interests Continued To Be Held By Transferor Servicing Assets Or Liabilities Prepayment Speed	6.40%	6.30%	6.20%	5.40%
Weighted average life (in years)	15.6	15.8	16.2	18.6