Derivative Financial Instruments - Information about Interest Rate Swap Agreements (Detail) - USD ($) $ in Millions	6 Months Ended	9 Months Ended
Jun. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Derivative [Line Items]
Notional Amount	$ 29,755		$ 26,977
Average Maturity (in years)	2 years 2 months 12 days	2 years 2 months 12 days
Estimated fair value gain (loss)	$ (10)	$ 10
Interest Payments On Variable Rate Commercial Real Estate Loans \| Cash flow hedges:
Derivative [Line Items]
Notional Amount	$ 25,905		$ 23,977
Average Maturity (in years)	1 year 8 months 12 days	1 year 8 months 12 days
Fixed	3.41%		3.45%
Variable	5.33%		5.36%
Estimated fair value gain (loss)	$ (1)	$ 11
Fixed Rate Long-Term Borrowings \| Fair value hedges:
Derivative [Line Items]
Notional Amount	$ 3,850		$ 3,000
Average Maturity (in years)	5 years 7 months 6 days	5 years 9 months 18 days
Fixed	3.48%		3.45%
Variable	5.53%		5.62%
Estimated fair value gain (loss)	$ (9)	$ (1)

Average fixed interest rate related to the group of interest rate derivatives.

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- Definition

Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

Average variable interest rate related to the group of interest rate derivatives.

+ References

No definition available.

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480237/815-40-50-5

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- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

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- Definition

Amount of unrealized gain (loss) related to the fair value of interest rate derivatives designated as fair value hedging instruments, as offset by the gain (loss) on the hedged item to the extent that the fair value hedge is determined to be effective.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Section 50
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-Section 50
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4C

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