Variable Interest Entities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Tax Credit Structures
Variable Interest Entity [Line Items]
Carrying amounts	$ 236.7	$ 248.2
Liabilities related to unfunded commitments	30.3	33.1
Leveraged Leasing Transactions
Variable Interest Entity [Line Items]
Funding of asset's cost via an equity interest	20.00%	20.00%
Funding of asset's cost via third party non recourse debt holders	80.00%	80.00%
Carrying amounts	$ 666.8	$ 673.6

Funding of asset's cost provided by third party non-recourse debt holders.

No definition available.

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- Definition

Funding of asset's cost via an equity ownership in a trust.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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- Details

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- Definition

Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph a

-URI http://asc.fasb.org/extlink&oid=7880789&loc=d3e5728-111685

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount of the liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

+ Details

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Balance Type:	credit
Period Type:	instant