Derivative financial instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Mar. 31, 2025	Sep. 30, 2025	Dec. 31, 2024
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value		$ 253	$ 255
Liability derivatives, fair value		480	822
Reduction in estimated fair value of interest rate contracts in asset position	$ (686)	(379)
Reduction in estimated fair value of interest rate contracts in liability position	$ (15)	(33)
Fair value hedges:
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value		192	206
Liability derivatives, fair value		451	787
Fair value hedges: \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value		13	6
Liability derivatives, fair value		0	3
Fair value hedges: \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value		48	43
Liability derivatives, fair value		29	32
Interest rate swap agreements \| Fair value hedges: \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value		12	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		1	4
Liability derivatives, fair value		0	0
Commitments to sell real estate loans \| Fair value hedges: \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value		28	39
Liability derivatives, fair value		6	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		20	4
Liability derivatives, fair value		23	32
Interest Rate Contracts \| Fair value hedges: \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value		174	185
Liability derivatives, fair value		435	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		18	21
Liability derivatives, fair value		$ 16	$ 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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