Netting Arrangements for Certain Financial Instruments and Securities Financing Activities - Additional Information (Detail) $ in Billions	Jun. 30, 2018 USD ($)
Derivative [Line Items]
Notional amount of derivative	$ 402.6
Over the Counter Trades [Member]
Derivative [Line Items]
Notional amount of derivative	214.1
Exchange Cleared [Member]
Derivative [Line Items]
Notional amount of derivative	167.7
Exchange Traded [Member]
Derivative [Line Items]
Notional amount of derivative	$ 20.8