Netting Arrangements for Certain Financial Instruments and Securities Financing Activities - Additional Information (Detail) $ in Billions	Sep. 30, 2018 USD ($)
Derivative [Line Items]
Notional amount of derivative	$ 407.7
Over the Counter Trades [Member]
Derivative [Line Items]
Notional amount of derivative	213.4
Exchange Cleared [Member]
Derivative [Line Items]
Notional amount of derivative	173.7
Exchange Traded [Member]
Derivative [Line Items]
Notional amount of derivative	$ 20.6