Contingent liabilities, contractual commitments and guarantees - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	$ 97,723	$ 96,410
Associates
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	$ 46,700	$ 48,500

The amount of the estimated financial effect of contingent liabilities. [Refer: Contingent liabilities [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 37
-IssueDate 2018-01-01
-Paragraph 86
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=37&date=2018-03-01&anchor=para_86_a&doctype=Standard
-URIDate 2018-03-16

Name:	ifrs-full_EstimatedFinancialEffectOfContingentLiabilities
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant