Derivative instruments - Hedged Items in Fair Value Hedging Relationships (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Derivative [Line Items]
Available-for-sale securities included in closed portfolios, subject to portfolio layer method, increase (decrease)	$ (156)	$ 1
Fair value hedging \| Securities – Available-for-sale
Derivative [Line Items]
Carrying amount of hedged asset or liability, Available-for-sale securities	55,743	46,420
Hedge accounting basis adjustment increase (decrease), Available-for-sale securities	(1,280)	(910)
Hedge accounting basis adjustment increase (decrease), discontinued hedges	(244)	(332)
Available-for-sale securities included in closed portfolios, subject to portfolio layer method	17,400	15,100
Available-for-sale securities included in closed portfolios, subject to portfolio layer method, increase (decrease)	(156)	1
Fair value hedging \| Securities – Available-for-sale \| Designated as hedging
Derivative [Line Items]
Available-for-sale securities included in closed portfolios, subject to portfolio layer method	11,900	8,900
Fair value hedging \| Loans
Derivative [Line Items]
Carrying amount of hedged asset or liability, Available-for-sale securities	2,811	2,939
Hedge accounting basis adjustment increase (decrease), Available-for-sale securities	(5)	(9)
Available-for-sale securities included in closed portfolios, subject to portfolio layer method	2,800	2,900
Available-for-sale securities included in closed portfolios, subject to portfolio layer method, increase (decrease)	(5)	(9)
Fair value hedging \| Loans \| Designated as hedging
Derivative [Line Items]
Available-for-sale securities included in closed portfolios, subject to portfolio layer method	1,400	1,400
Fair value hedging \| Long-term debt
Derivative [Line Items]
Carrying amount of hedged asset or liability, Long-term debt	28,522	28,375
Hedge accounting basis adjustment increase (decrease), Long-term debt	(617)	(264)
Hedged liability, discontinued fair value hedge, cumulative increase (decrease)	$ 11	$ 10

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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Amount of cumulative increase (decrease) in fair value of hedged asset in fair value hedge, attributable to hedged risk, remaining after discontinued hedge. Excludes cumulative basis adjustment related to foreign exchange risk.

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