Accounting for Transfers and Servicing of Financial Assets and Variable Interest Entities - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Minimum [Member]
Variable Interest Entity [Line Items]
Aggregate amount of investments in unconsolidated VIEs	$ 1,000,000	$ 1,000,000
Maximum [Member]
Variable Interest Entity [Line Items]
Aggregate amount of investments in unconsolidated VIEs	53,000,000	37,000,000
Conduit [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	35,000,000	116,000,000
Tender Option Bond Program [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	2,900,000,000	4,600,000,000
Liabilities related to consolidated VIEs	2,700,000,000	4,600,000,000
Community Development and Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Federal and state income tax credits recognized in tax expense	773,000,000	758,000,000	683,000,000
Expense related to investments	771,000,000	934,000,000	805,000,000
Expenses related to investments recognized in tax expense	258,000,000	297,000,000	282,000,000
Investment tax credits	937,000,000	780,000,000	200,000,000
Assets related to consolidated VIEs	2,700,000,000	2,500,000,000
Liabilities related to consolidated VIEs	2,000,000,000	1,800,000,000
Investment carrying amount	4,259,000,000	4,178,000,000
Maximum exposure to loss	8,393,000,000	7,390,000,000
Private Investment Funds and Partnerships [Member]
Variable Interest Entity [Line Items]
Investment carrying amount	94,000,000	98,000,000
Maximum exposure to loss	$ 105,000,000	$ 107,000,000

Expenses related to investments.

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- Definition

Expenses Related To Investments Recognized In Tax Expense

+ References

No definition available.

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- Definition

Federal and state income tax credits recognized in tax expense.

+ References

No definition available.

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- Definition

Investment Tax Credits

+ References

No definition available.

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- Definition

The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (bb)

-URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5710-111685

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- Definition

The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.

+ References

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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

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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

Net carrying amount of the assets and 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), when the reporting entity is not the VIE's primary beneficiary.

+ References

No definition available.

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