OTHER RESERVES (Details) - Schedule of Merger Reserve - Hedges of net investment in foreign operations [member] - GBP (£) £ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Merger reserve
Beginning Balance	£ 7,766	£ 7,766	£ 7,766
Redemption of preference shares (note 41)	(3)
Ending Balance	£ 7,763	£ 7,766	£ 7,766

The cash outflow to acquire equity or debt instruments of other entities (other than payments for those instruments considered to be cash equivalents or those held for dealing or trading purposes), classified as investing activities.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 7
-IssueDate 2019-01-01
-Paragraph 16
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=7&code=ifrs-tx-2019-en-r&anchor=para_16_c&doctype=Standard
-URIDate 2019-03-27

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