TAX EXPENSE (Details) - Schedule of Tax Charges - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	[1]	Dec. 31, 2017	[1]
TAX EXPENSE (Details) - Schedule of Tax Charges [Line Items]
Current tax expense	£ (1,361)	£ (1,298)		£ (1,148)
Deferred tax expense	(26)	(156)		(478)
Tax expense	(1,387)	(1,454)		(1,626)
UK Corporation Tax [Member]
TAX EXPENSE (Details) - Schedule of Tax Charges [Line Items]
Current tax on profit for the year	(1,389)	(1,280)		(1,240)
Adjustments in respect of prior years	96	11		122
Current tax expense	(1,293)	(1,269)		(1,118)
Foreign Tax [Member]
TAX EXPENSE (Details) - Schedule of Tax Charges [Line Items]
Current tax on profit for the year	(70)	(34)		(40)
Adjustments in respect of prior years	2	5		10
Current tax expense	(68)	(29)		(30)
DeferredTax[Member]
TAX EXPENSE (Details) - Schedule of Tax Charges [Line Items]
Current year	(165)	(127)		(430)
Adjustments in respect of prior years	£ 139	£ (29)		£ (48)

[1] Restated, see note 1.