Derivative financial instruments - Information about Interest Rate Swap Agreements (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2026	Dec. 31, 2025
Derivative [Line Items]
Notional Amount	$ 32,300	$ 31,000
Weighted-Average Maturity (In years)	1 year 8 months 12 days	2 years
Estimated fair value gain (loss)	$ (17)	$ (15)
Fair value hedges:
Derivative [Line Items]
Impact of estimated fair value gain (losses) on hedging instruments	(92)	(6)
Fair value hedges: \| Forward-Starting Interest Rate Swap Agreements
Derivative [Line Items]
Notional Amount		1,800
Cash flow hedges:
Derivative [Line Items]
Impact of estimated fair value gain (losses) on hedging instruments	(61)	96
Cash flow hedges: \| Forward-Starting Interest Rate Swap Agreements
Derivative [Line Items]
Notional Amount	10,200	9,700
Interest Payments On Variable Rate Commercial Real Estate Loans \| Cash flow hedges:
Derivative [Line Items]
Notional Amount	$ 26,200	$ 24,900
Weighted-Average Maturity (In years)	1 year 1 month 6 days	1 year 3 months 18 days
Fixed	3.70%	3.63%
Variable	3.63%	3.81%
Estimated fair value gain (loss)	$ (7)	$ (6)
Fixed Rate Long-Term Borrowings \| Fair value hedges:
Derivative [Line Items]
Notional Amount	$ 6,100	$ 6,100
Weighted-Average Maturity (In years)	4 years 3 months 18 days	4 years 9 months 18 days
Fixed	3.56%	3.56%
Variable	3.79%	4.02%
Estimated fair value gain (loss)	$ (10)	$ (9)

Impact in estimated fair value gain (losses ) on hedging instruments.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-5

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
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-Name Accounting Standards Codification
-Section 50
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- Definition

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

+ References

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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/2009/role/commonPracticeRef
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- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

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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://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
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