Variable Interest Entities - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Tax Credit Structures
Variable Interest Entity [Line Items]
Carrying amounts	$ 208,900,000	$ 222,300,000
Exposure to loss from liquidity arrangements and obligations to purchase assets	0
Liabilities related to unfunded commitments	15,600,000	19,800,000
Affordable housing tax credits and other tax benefits	58,100,000
Leveraged Leasing Transactions
Variable Interest Entity [Line Items]
Carrying amounts	547,600,000	671,200,000
Exposure to loss from liquidity arrangements and obligations to purchase assets	$ 0
Leveraged Leasing Transactions \| Lower Limit
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	70.00%	70.00%
Leveraged Leasing Transactions \| Upper Limit
Variable Interest Entity [Line Items]
Funding of asset's cost via an equity interest	30.00%	30.00%
Funding of asset's cost via third party non recourse debt holders	80.00%	80.00%

Affordable Housing Tax Credits and Other Tax Benefits

No definition available.

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- Definition

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

+ References

No definition available.

+ Details

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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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- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

+ 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 b

-URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5728-111685

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5747-111685

+ Details

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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

+ Details

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- 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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- Details

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- Details

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