Commitments, Contingencies and Guarantees - External Credit Ratings of Underlying or Referenced Assets for Credit Related Derivatives Contracts (Detail) $ in Millions	Aug. 31, 2016 USD ($)
Index credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	$ 107.7
Single name credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	242.7
Below Investment Grade [Member] | Index credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	0.0
Below Investment Grade [Member] | Single name credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	144.2
AAA/Aaa [Member] | Index credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	24.0
AAA/Aaa [Member] | Single name credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	0.0
AA/Aa [Member] | Index credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	0.0
AA/Aa [Member] | Single name credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	0.0
A [Member] | Index credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	0.0
A [Member] | Single name credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	59.9
BBB/Baa [Member] | Index credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	83.7
BBB/Baa [Member] | Single name credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	$ 38.6