Note Transfers of financial assets and servicing assets (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, 2019	Mar. 31, 2018
Assumption for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Line Items]
Prepayment speed	6.30%	5.60%
Weighted average life	9 years 11 months	9 years 1 month
Discount rate (annual rate)	11.00%	10.80%