Netting Arrangements for Certain Financial Instruments and Securities Financing Activities - Additional Information (Detail) $ in Billions	Mar. 31, 2018 USD ($)
Derivative [Line Items]
Notional amount of derivative	$ 401.5
Over the Counter Trades [Member]
Derivative [Line Items]
Notional amount of derivative	207.4
Exchange Cleared [Member]
Derivative [Line Items]
Notional amount of derivative	169.1
Exchange Traded [Member]
Derivative [Line Items]
Notional amount of derivative	$ 25.0