Trading liabilities - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Financial Instruments [Abstract]
Gains (losses) on financial liabilities at fair value through profit or loss, classified as held for trading	$ 543	$ 2

The gains (losses) on financial liabilities at fair value through profit or loss classified as held for trading. [Refer: Financial liabilities at fair value through profit or loss; Gains (losses) on financial liabilities at fair value through profit or loss]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2017-01-01
-Paragraph 20
-Subparagraph a
-Clause i
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_20_a_i&doctype=Standard
-URIDate 2017-03-09

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration