The aggregate amount of recurring noncash expense charged against earnings in the period to allocate the cost of assets over their estimated remaining economic lives.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Fair value of investment in certain entities that calculate net asset value per share. Includes, but is not limited to, by unit, membership interest, or other ownership interest. Investment includes, but is not limited to, investment in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds. Excludes measurement of net asset value as estimate of fair value.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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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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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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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Variable Interest Entities - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Variable Interest Entity [Line Items]
Investments in operating partnerships	$ 212,000,000		$ 178,000,000
Liabilities related to investments in qualified affordable housing projects	5,000,000		5,000,000
Recurring [Member]
Variable Interest Entity [Line Items]
Fair value of indirect principal investments	153,000,000		191,000,000
Recurring [Member] \| Principal Investments Indirect [Member]
Variable Interest Entity [Line Items]
Fair value of indirect principal investments	138,000,000		158,000,000
LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Investments in operating partnerships	6,049,000,000		4,814,000,000
Liabilities related to investments in qualified affordable housing projects	2,871,000,000		2,003,000,000
Tax credit of investment	115,000,000	$ 98,000,000
LIHTC Investments [Member] \| Qualified affordable housing projects investment [Member]
Variable Interest Entity [Line Items]
Liabilities related to investments in qualified affordable housing projects	447,000,000		462,000,000
LIHTC Investments [Member] \| Accrued Income And Other Assets [Member]
Variable Interest Entity [Line Items]
Investments in operating partnerships	1,300,000,000		1,200,000,000
LIHTC Investments [Member] \| Investments [Member]
Variable Interest Entity [Line Items]
Amortization of investment	124,000,000	$ 96,000,000
Guaranteed Funds [Member] \| Investments [Member]
Variable Interest Entity [Line Items]
VIE, assets that can only be used to settle obligations	3,000,000		1,000,000
VIE, liabilities	$ 0		$ 0