Securitization Activities - Summary of Retained Interests in SPEs (Parenthetical) (Detail) (Subsequent event [Member], USD $) In Millions, unless otherwise specified	Sep. 23, 2013
U.S. government agency residential mortgage-backed securities [Member] \| Current year securities [Member]
Securitization Vehicles [Line Items]
Retained interests	$ 285.0
U.S. government agency residential mortgage-backed securities [Member] \| Previous year securities [Member]
Securitization Vehicles [Line Items]
Retained interests	57.9
U.S. government agency commercial mortgage-backed securities [Member] \| Current year securities [Member]
Securitization Vehicles [Line Items]
Retained interests	91.0
U.S. government agency commercial mortgage-backed securities [Member] \| Previous year securities [Member]
Securitization Vehicles [Line Items]
Retained interests	13.0
Collateralized loan obligations securitizations [Member] \| Current year securities [Member]
Securitization Vehicles [Line Items]
Retained interests	$ 9.3

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the interests continued to be held by a transferor (retained or residual interest) after transferring financial assets to a third party.

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