Variable Interest Entities and Other Investments - Carrying Amounts Related to Unconsolidated VIEs (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012
Variable Interest Entity [Line Items]
Unconsolidated VIEs, Total Assets	$ 905
Unconsolidated VIEs, Total Liabilities	34
Unconsolidated VIEs, Maximum Exposure to Loss	1,192
LIHC investments [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs, Total Assets	526
Unconsolidated VIEs, Total Liabilities	34
Unconsolidated VIEs, Maximum Exposure to Loss	808
Renewable energy investments [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs, Total Assets	364
Unconsolidated VIEs, Maximum Exposure to Loss	364
Private capital investment [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs, Total Assets	15
Unconsolidated VIEs, Maximum Exposure to Loss	$ 20

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

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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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

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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

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