Derivative instruments - Gains (Losses) Related to Hedging Derivative Portfolio Recognized in the Income Statement (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Derivative Instruments, Gain (Loss) [Line Items]
Gain recognized in the consolidated income statement due to fair value and cash flow hedging relationships	$ 7	$ 3	$ 2	$ 10	$ 12
Interest rate contracts \| Securities available-for-sale \| Interest revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized on derivatives	866	1,484	(325)	2,350	466
Gain or (loss) recognized on hedged item	(858)	(1,480)	322	(2,338)	(463)
Interest rate contracts \| Long-term debt \| Interest expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized on derivatives	(292)	(741)	22	(1,033)	(331)
Gain or (loss) recognized on hedged item	291	740	(21)	1,031	330
FX contracts \| Staff expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) on cash flow hedges	(1)	0	4	(1)	9
FX contracts \| Securities available-for-sale
Derivative Instruments, Gain (Loss) [Line Items]
Gain from components excluded from assessment of fair value hedge effectiveness, net (less than)	1	1	1	1	1
FX contracts \| Securities available-for-sale \| Foreign exchange revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized on derivatives	(1)	(1)	(1)	(2)	7
Gain or (loss) recognized on hedged item	$ 2	$ 1	$ 1	$ 3	$ (6)

Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

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Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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Net gain (loss) relating to components of the gain (loss) on the fair value hedging instrument excluded from the assessment of fair value hedge effectiveness. Recognized in earnings.

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Amount, before tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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