Contingent liabilities and commitments - Schedule of Contingent Liabilities (Details) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Contingent liabilities
Acceptances and endorsements	£ 73	£ 71
Other items serving as direct credit substitutes	901	740
Performance bonds and other transaction-related contingencies	2,306	2,300
Total Contingent liabilities	3,207	3,040
Total contingent liabilities	£ 3,280	£ 3,111

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 2016-01-13
-Paragraph 86
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=37&date=2016-03-30&anchor=para_86_a&doctype=Standard
-URIDate 2016-03-31

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