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
	Mar. 31, 2018	Mar. 31, 2017
Assumption for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Line Items]
Prepayment speed	5.60%	4.40%
Weighted average life (in years)	9 years 1 month	10 years 11 months
Discount rate (annual rate)	10.80%	11.00%