DERIVATIVE FINANCIAL INSTRUMENTS (Details) - GBP (£) £ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Disclosure of derivative financial instruments [text block] [Abstract]
Hedged Liability, Fair Value Hedge	£ 692	£ 170
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	£ 101

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=112277219&loc=d3e80748-113994

Name:	us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration