TRADING AND OTHER FINANCIAL ASSETS AT FAIR VALUE THROUGH PROFIT OR LOSS (Details) - GBP (£) £ in Millions	Dec. 31, 2017	Dec. 31, 2016
TRADING AND OTHER FINANCIAL ASSETS AT FAIR VALUE THROUGH PROFIT OR LOSS (Details) [Line Items]
Trading and other financial assets at fair value through profit or loss	£ 162,878	£ 151,174
Insurance contracts [member]
TRADING AND OTHER FINANCIAL ASSETS AT FAIR VALUE THROUGH PROFIT OR LOSS (Details) [Line Items]
Trading and other financial assets at fair value through profit or loss	117,323	101,888
Insurance contracts [member] \| Unconsolidated structured entities [member]
TRADING AND OTHER FINANCIAL ASSETS AT FAIR VALUE THROUGH PROFIT OR LOSS (Details) [Line Items]
Trading and other financial assets at fair value through profit or loss	28,759	15,611
Insurance contracts [member] \| Equity investments [member]
TRADING AND OTHER FINANCIAL ASSETS AT FAIR VALUE THROUGH PROFIT OR LOSS (Details) [Line Items]
Trading and other financial assets at fair value through profit or loss	£ 1,944	£ 2,245

The amount of financial assets that are measured at fair value and for which gains (losses) are recognised in profit or loss. A financial asset shall be measured at fair value through profit or loss unless it is measured at amortised cost or at fair value through other comprehensive income. A gain (loss) on a financial asset measured at fair value shall be recognised in profit or loss unless it is part of a hedging relationship, it is an investment in an equity instrument for which the entity has elected to present gains and losses in other comprehensive income or it is a financial asset measured at fair value through other comprehensive income. [Refer: At fair value [member]; Financial assets]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2016-01-13
-Paragraph 8
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2016-03-30&anchor=para_8_a&doctype=Standard
-URIDate 2016-03-31

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