Commitments, Contingencies and Guarantees - External Credit Ratings of Underlying or Referenced Assets for Credit Related Derivatives Contracts (Detail) $ in Millions	Feb. 28, 2017 USD ($)
Index credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	$ 4.0
Single name credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	355.2
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	180.2
AAA/Aaa [Member] | Index credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	4.0
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	115.1
BBB/Baa [Member] | Index credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	0.0
BBB/Baa [Member] | Single name credit default swaps [Member]
Credit Derivatives [Line Items]
External credit ratings	$ 59.9