Variable Interest Entities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
Nov. 30, 2011	Dec. 31, 2011	Sep. 30, 2012
Investment Funds
Variable Interest Entity [Line Items]
Purchase of securities at par from three investment funds	$ 90
Net assets held by the Funds		16,500
Pre-tax charge		2
Maximum exposure			0
Tax Credit Structures
Variable Interest Entity [Line Items]
Carrying amounts		264.9	259.9
Liabilities related to unfunded commitments		44.5	36.8
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		$ 714.5	$ 671.0

Charge incurred in connection with purchase of securities from funds.

No definition available.

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Period Type:	duration

- 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 net of assets and liabilities.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 09

-Paragraph 19

-Article 6

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 225

-Section S99

-Paragraph 3

-Subparagraph (SX 210.6-09.6,7)

-URI http://asc.fasb.org/extlink&oid=6488393&loc=d3e606914-122999

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 210

-Section S99

-Paragraph 2

-Subparagraph (SX 210.6-05.4)

-URI http://asc.fasb.org/extlink&oid=6488278&loc=d3e604008-122996

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 05

-Paragraph 4

-Article 6

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Aggregate cash payments for a combination of transactions that are classified as investing activities in which assets, which may include securities, other types of investments, or productive assets, are purchased from third-party sellers. This element can be used by entities to aggregate payments for all asset purchases that are classified as investing activities.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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=7880789&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=7880789&loc=d3e5747-111685

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS140-4/FIN46(R)

-Paragraph C6

-Subparagraph b

-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.

+ 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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Balance Type:	debit
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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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