The amount deducted from an entities' taxes, reflecting a percentage of an amount invested in certain assets spread over the useful life of those assets; includes deferred investment tax credits.

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Amount of financial support provided to a nonconsolidated legal entity that is required to comply with or operate in accordance with requirements that are similar to those included in Rule 2a-7 of the Investment Company Act of 1940 for registered money market funds.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

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

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

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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.

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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.

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Expenses related to investments.

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Expenses Related To Investments Recognized In Tax Expense

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Federal and state income tax credits recognized in tax expense.

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Accounting for Transfers and Servicing of Financial Assets and Variable Interest Entities - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Minimum [Member]
Variable Interest Entity [Line Items]
Aggregate amount of investments in unconsolidated VIEs	$ 1,000,000		$ 1,000,000		$ 1,000,000
Maximum [Member]
Variable Interest Entity [Line Items]
Aggregate amount of investments in unconsolidated VIEs	57,000,000		57,000,000		40,000,000
Financial Support Waived Fees [Member]
Variable Interest Entity [Line Items]
Financial or other support to money market funds	6,000,000	$ 9,000,000	17,000,000	$ 35,000,000
Private Investment Funds and Partnerships [Member]
Variable Interest Entity [Line Items]
Investment carrying amount	28,000,000		28,000,000		28,000,000
Maximum exposure to loss	49,000,000		49,000,000		50,000,000
Community Development and Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Federal and state income tax credits recognized in tax expense	173,000,000	172,000,000	495,000,000	504,000,000
Expense related to investments	163,000,000	169,000,000	464,000,000	476,000,000
Investment tax credits	361,000,000	219,000,000	843,000,000	850,000,000
Expenses related to investments recognized in tax expense	61,000,000	$ 61,000,000	187,000,000	$ 194,000,000
Investment carrying amount	5,580,000,000		5,580,000,000		5,009,000,000
Maximum exposure to loss	11,090,000,000		11,090,000,000		10,373,000,000
Assets related to consolidated VIEs	3,600,000,000		3,600,000,000		3,500,000,000
Liabilities related to consolidated VIEs	2,600,000,000		2,600,000,000		2,600,000,000
Conduit [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	23,000,000		23,000,000		24,000,000
Tender Option Bond Program [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	2,100,000,000		2,100,000,000		1,100,000,000
Liabilities related to consolidated VIEs	$ 2,000,000,000		$ 2,000,000,000		$ 1,100,000,000