Summary of Other Noninterest Expense (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended	1 Months Ended
Dec. 31, 2010	May 02, 2011 5.70% Senior Notes	May 02, 2011 6.05% Subordinated Notes
Other Noninterest Expense [Line Items]
Repurchases of principal amount of 5.70% Senior Notes and 6.05% Subordinated Notes	$ 312.6	$ 108.6	$ 204.0

The cash outflow for a borrowing supported by a written promise to pay an obligation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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