Note Transfers of financial assets and servicing rights (Key economic assumptions used in measuring the SR retained at the date of the residential mortgage loan securitizations and whole loan sales by the banking subs) (Detail) - Residential Mortgage	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Assumption for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Line Items]
Prepayment speed	4.90%	4.60%	4.30%	5.20%
Weighted average life (in years)	10 years 6 months	10 years 7 months	10 years 11 months	10 years 1 month
Discount rate (annual rate)	10.90%	11.00%	10.90%	11.00%