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Derivative financial instruments - Information about Interest Rate Swap Agreements (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Mar. 31, 2025 | Sep. 30, 2025 | Dec. 31, 2024
Derivative [Line Items] |  |  |
Notional Amount |  | $ 31,100 | $ 36,184
Weighted-Average Maturity (In years) | 2 years 2 months 12 days | 2 years 2 months 12 days |
Estimated fair value gain (loss) | $ (1) | $ 12 |
Fair value hedges: |  |  |
Derivative [Line Items] |  |  |
Impact of estimated fair value gain (losses) on hedging instruments | (153) | 1 |
Fair value hedges: | Forward-Starting Interest Rate Swap Agreements |  |  |
Derivative [Line Items] |  |  |
Notional Amount |  | 2,800 | 3,400
Cash flow hedges: |  |  |
Derivative [Line Items] |  |  |
Impact of estimated fair value gain (losses) on hedging instruments | $ (136) | 83 |
Cash flow hedges: | Forward-Starting Interest Rate Swap Agreements |  |  |
Derivative [Line Items] |  |  |
Notional Amount |  | 10,400 | 10,000
Interest Payments On Variable Rate Commercial Real Estate Loans | Cash flow hedges: |  |  |
Derivative [Line Items] |  |  |
Notional Amount |  | $ 25,000 | $ 30,819
Weighted-Average Maturity (In years) | 1 year 7 months 6 days | 1 year 6 months |
Fixed |  | 3.65% | 3.41%
Variable |  | 4.28% | 4.47%
Estimated fair value gain (loss) | $ 1 | $ 8 |
Fixed Rate Long-Term Borrowings | Fair value hedges: |  |  |
Derivative [Line Items] |  |  |
Notional Amount |  | $ 6,100 | $ 5,350
Weighted-Average Maturity (In years) | 5 years 10 months 24 days | 5 years 1 month 6 days |
Fixed |  | 3.56% | 3.55%
Variable |  | 4.26% | 4.71%
Estimated fair value gain (loss) | $ (2) | $ 4 |
Fixed Rate Available For Sale Securities | Fair value hedges: |  |  |
Derivative [Line Items] |  |  |
Notional Amount |  |  | $ 15
Weighted-Average Maturity (In years) | 1 month 6 days |  |
Fixed |  |  | 4.84%
Variable |  |  | 4.36%
Estimated fair value gain (loss) | $ 0 |  |

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- Definition Average fixed interest rate related to the group of interest rate derivatives. + References No definition available. + Details
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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. + 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 20 -Name Accounting Standards Codification -Section 25 -Paragraph 6A -Publisher FASB -URI https://asc.fasb.org/1943274/2147480682/815-20-25-6A Reference 2: 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 + Details
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