Commitments, Contingencies and Guarantees - External Credit Ratings of Underlying or Referenced Assets for Credit Related Derivatives Contracts (Detail) (USD $) In Millions, unless otherwise specified	Feb. 28, 2014
Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	$ 335.0
Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	51.0
AAA/Aaa [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	335.0
AAA/Aaa [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0
AA/Aa [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0
AA/Aa [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0
A [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0
A [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0
BBB/Baa [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0
BBB/Baa [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	46.0
Below Investment Grade [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0
Below Investment Grade [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	5.0
Unrated [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	0
Unrated [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	$ 0