Netting Arrangements for Certain Financial Instruments and Securities Financing Activities - Additional Information (Detail) $ in Billions	Sep. 30, 2017 USD ($)
Derivative [Line Items]
Notional amount of derivative	$ 355.4
Over the Counter Trades [Member]
Derivative [Line Items]
Notional amount of derivative	187.3
Exchange Cleared [Member]
Derivative [Line Items]
Notional amount of derivative	163.0
Exchange Traded [Member]
Derivative [Line Items]
Notional amount of derivative	$ 5.1