Derivative financial instruments - Summary of changes in fair value, hedges used to calculate ineffectiveness (Details) - Fair value hedges - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Interest rate risk on finance debt
Disclosure of detailed information about hedges [line items]
Change in fair value of hedging instrument used to calculate ineffectiveness	$ (258)	$ (764)
Change in fair value of hedged item used to calculate ineffectiveness	258	737
Gain (loss) on hedge ineffectiveness recognised in profit or loss	0	27
Interest rate and foreign currency risk on finance debt
Disclosure of detailed information about hedges [line items]
Change in fair value of hedging instrument used to calculate ineffectiveness	(2,743)	(336)
Change in fair value of hedged item used to calculate ineffectiveness	2,549	286
Gain (loss) on hedge ineffectiveness recognised in profit or loss	$ 194	$ 50

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The gain (loss) on the change in fair value of the hedged item used as a basis for recognising hedge ineffectiveness. Hedge ineffectiveness is the extent to which the changes in the fair value or the cash flows of the hedging instrument are greater or less than those on the hedged item.

+ References

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The gain (loss) on the change in fair value of the hedging instrument used as a basis for recognising hedge ineffectiveness. Hedge ineffectiveness is the extent to which the changes in the fair value or the cash flows of the hedging instrument are greater or less than those on the hedged item.

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The gain (loss) recognised in profit or loss on hedge ineffectiveness. [Refer: Gain (loss) on hedge ineffectiveness]

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