Fair values of financial instruments carried at fair value - Sensitivity of Level 3 fair values to reasonably possible alternative assumptions (Details) $ in Millions	6 Months Ended
Jun. 30, 2021 USD ($) category	Dec. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Favourable changes reflected in profit or loss	$ 998	$ 908	$ 924
Unfavourable changes reflected in profit or loss	(1,014)	(922)	(921)
Favourable changes recognized in OCI	105	110	101
Unfavourable changes recognized in OCI	$ (104)	(110)	(104)
Number of financial instrument categories \| category	1
Confidence level	95.00%
Derivatives, trading assets and trading liabilities \| Derivatives, trading liabilities
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Favourable changes reflected in profit or loss	$ 179	229	271
Unfavourable changes reflected in profit or loss	(197)	(244)	(268)
Favourable changes recognized in OCI	0	0	0
Unfavourable changes recognized in OCI	0	0	0
Financial assets designated and otherwise mandatorily measured at fair value through profit or loss \| Financial liabilities designated at fair value
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Favourable changes reflected in profit or loss	795	644	625
Unfavourable changes reflected in profit or loss	(793)	(643)	(625)
Favourable changes recognized in OCI	0	0	0
Unfavourable changes recognized in OCI	0	0	0
Financial investments
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Favourable changes reflected in profit or loss	24	35	28
Unfavourable changes reflected in profit or loss	(24)	(35)	(28)
Favourable changes recognized in OCI	105	110	101
Unfavourable changes recognized in OCI	$ (104)	$ (110)	$ (104)

[Line Items] for Disclosure Of Fair Value Measurement Of Assets And Liabilities [Table]

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- Definition

Gain (Loss) Recognized In Other Comprehensive Income Due to Favourable Changes In Significant Unobservable Inputs

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- Definition

Gain (Loss) Recognized In Other Comprehensive Income Due to Unfavourable Changes In Significant Unobservable Inputs

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- Definition

Gain (Loss) Recognized In Profit Or Loss Due to Favourable Changes In Significant Unobservable Inputs

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- Definition

Gain (Loss) Recognized In Profit Or Loss Due to Unfavourable Changes In Significant Unobservable Inputs

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- Definition

Number Of Financial Instrument Categories

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- Definition

The confidence level corresponding to the results of a technique other than the confidence level technique used for determining the risk adjustment for non-financial risk. [Refer: Risk adjustment for non-financial risk [member]]

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2021-01-01
-Name IFRS
-Number 17
-IssueDate 2020-01-01
-Paragraph 119
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=17&code=ifrs-tx-2020-en-r&anchor=para_119&doctype=Standard
-URIDate 2020-01-01

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