Derivative financial instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2025	Dec. 31, 2024
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	$ 265	$ 255
Liability derivatives, fair value	554	822
Reduction in estimated fair value of interest rate contracts in asset position	(440)	(686)
Reduction in estimated fair value of interest rate contracts in liability position	(32)	(15)
Fair value hedges:
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	194	206
Liability derivatives, fair value	518	787
Fair value hedges: \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	27	6
Liability derivatives, fair value	4	3
Fair value hedges: \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	44	43
Liability derivatives, fair value	32	32
Interest rate swap agreements \| Fair value hedges: \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	24	2
Liability derivatives, fair value	0	3
Commitments to sell real estate loans \| Fair value hedges: \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	3	4
Liability derivatives, fair value	4	0
Commitments to sell real estate loans \| Fair value hedges: \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	27	39
Liability derivatives, fair value	7	0
Commitments to originate real estate loans for sale \| Fair value hedges: \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	17	4
Liability derivatives, fair value	25	32
Interest Rate Contracts \| Fair value hedges: \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	168	185
Liability derivatives, fair value	493	769
Foreign exchange and other option and futures contracts \| Fair value hedges: \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	26	21
Liability derivatives, fair value	$ 25	$ 18

Increase (decrease) in estimated fair value of interest rate contracts in asset position.

No definition available.

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- Definition

Increase (decrease) in estimated fair value of interest rate contracts in liability position.

+ References

No definition available.

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- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

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- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ 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.

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