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RETIREMENT BENEFIT OBLIGATIONS (Details) - Schedule of Movements in Defined Benefit Obligation - Movements in the defined benefit obligation [Member] - GBP (£)
£ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
RETIREMENT BENEFIT OBLIGATIONS (Details) - Schedule of Movements in Defined Benefit Obligation [Line Items]    
At 1 January £ (41,092) £ (44,384)
Current service cost (201) (261)
Interest expense (1,172) (1,130)
Remeasurements:    
Actuarial losses – experience (29) (439)
Actuarial (losses) gains – demographic assumptions 471 (201)
Actuarial gains (losses) – financial assumptions (5,400) 2,347
Benefits paid 2,174 3,079
Past service cost (44) (108)
Curtailments   (12)
Settlements 17 17
Exchange and other adjustments 35  
At 31 December £ (45,241) £ (41,092)