Commitments, Contingencies and Guarantees - External Credit Ratings of Underlying or Referenced Assets for Credit Related Derivatives Contracts (Detail) $ in Millions	Aug. 31, 2015 USD ($)
Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	$ 1,746.9
Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	228.6
Below Investment Grade [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0.0
Below Investment Grade [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	134.5
Unrated [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0.0
Unrated [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	50.6
AAA/Aaa [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	1,746.9
AAA/Aaa [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0.0
AA/Aa [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0.0
AA/Aa [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0.0
A [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0.0
A [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	22.0
BBB/Baa [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0.0
BBB/Baa [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	$ 21.5