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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)

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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 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-5 + Details
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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 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-5 + Details
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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 -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 5A -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-5A Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 505 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 18 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481112/505-10-50-18 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 815 -SubTopic 20 -Name Accounting Standards Codification -Section 25 -Paragraph 6A -Publisher FASB -URI https://asc.fasb.org/1943274/2147480682/815-20-25-6A + Details
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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 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4C -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4C Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4A -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A + Details
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