v3.26.1
FINANCIAL INSTRUMENTS - Summary of Reconciliation of Fair Value Measurement in Level 3 of the Fair Value Hierarchy (Details)
£ in Millions
 6 Months Ended
Jun. 30, 2026
GBP (£)
Assets  
Beginning balance £ 266,837
Ending Balance 312,275
Financial Liabilities [Abstract]  
Beginning balance (251,689)
Ending Balance (295,259)
Level 3 | Other financial assets at FVTPL  
Assets  
Beginning balance 64
Fair value movements 0
Settlements (11)
Ending Balance 53
Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the period 0
Level 3 | Financial assets at fair value  
Assets  
Beginning balance 94
Fair value movements 0
Settlements (13)
Ending Balance 81
Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the period 0
Level 3 | Derivatives  
Assets  
Beginning balance 30
Fair value movements 0
Settlements (2)
Ending Balance 28
Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the period 0
Level 3 | Derivatives  
Financial Liabilities [Abstract]  
Beginning balance (13)
Fair value movements 1
Settlements 0
Ending Balance (12)
Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the year 1
Level 3 | Financial liabilities at fair value  
Financial Liabilities [Abstract]  
Beginning balance (13)
Fair value movements 1
Settlements 0
Ending Balance (12)
Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the year £ 1