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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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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Accounting for Transfers and Servicing of Financial Assets and Variable Interest Entities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Minimum [Member]
Variable Interest Entity [Line Items]
Aggregate amount of investments in unconsolidated VIEs	$ 1		$ 1		$ 1
Maximum [Member]
Variable Interest Entity [Line Items]
Aggregate amount of investments in unconsolidated VIEs	89		89		95
Financial Support Waived Fees [Member]
Variable Interest Entity [Line Items]
Financial or other support to money market funds	8	$ 6	22	$ 18
Private Investment Funds and Partnerships [Member]
Variable Interest Entity [Line Items]
Investment carrying amount	30		30		27
Maximum exposure to loss	55		55		52
Community Development and Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Federal and state income tax credits recognized in tax expense	132	150	423	486
Expense related to investments	122	133	391	434
Investment tax credits	80	90	326	368
Expenses related to investments recognized in tax expense	80	$ 67	237	$ 202
Investment carrying amount	6,079		6,079		5,823
Maximum exposure to loss	12,163		12,163		12,360
Assets related to consolidated VIEs	3,900		3,900		3,900
Liabilities related to consolidated VIEs	3,100		3,100		2,700
Conduit [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	14		14		14
Tender Option Bond Program [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	2,900		2,900		2,400
Liabilities related to consolidated VIEs	$ 2,600		$ 2,600		$ 2,300