EVENTS SINCE THE BALANCE SHEET DATE (Details) £ in Billions	12 Months Ended
Dec. 31, 2017 GBP (£)
Top of range [member] \| Major ordinary share transactions [member]
EVENTS SINCE THE BALANCE SHEET DATE (Details) [Line Items]
Payments to acquire or redeem entity's shares	£ 1

The cash outflow to acquire or redeem entity's shares.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 7
-IssueDate 2016-01-13
-Paragraph 17
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2016-03-30&anchor=para_17_b&doctype=Standard
-URIDate 2016-03-31

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