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, 2013
Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	$ 283.0
Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	506.5
AAA/Aaa [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings
AAA/Aaa [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	506.5
AA/Aa [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings
AA/Aa [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings
A [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	10.0
A [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings
BBB/Baa [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	243.0
BBB/Baa [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings
Below Investment Grade [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings	30.0
Below Investment Grade [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings
Unrated [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings
Unrated [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
External credit ratings