v3.26.1
DEBT SECURITIES IN ISSUE (Details)
£ in Millions, € in Billions, $ in Billions
Jun. 30, 2026
GBP (£)
Jun. 30, 2026
EUR (€)
Jun. 30, 2026
USD ($)
Dec. 31, 2025
GBP (£)
Dec. 31, 2025
EUR (€)
Dec. 31, 2025
USD ($)
Jun. 30, 2025
EUR (€)
Debt Securities In Issue [Line Items]              
Notional amount £ 341,548     £ 266,336      
Debt securities 47,255     41,388      
Medium-term notes              
Debt Securities In Issue [Line Items]              
Debt securities 2,220     2,290      
Downstreamed from Santander UK Group Holdings plc to Santander UK plc              
Debt Securities In Issue [Line Items]              
Debt securities 10,498     9,606      
Euro €35bn Global Covered Bond Programme              
Debt Securities In Issue [Line Items]              
Notional amount | €   € 35     € 35   € 35
Debt securities 18,073     19,201      
£10bn Global Covered Bond Programme              
Debt Securities In Issue [Line Items]              
Notional amount 10,000     10,000      
Debt securities 3,713     0      
US $20bn Commercial Paper Programmes              
Debt Securities In Issue [Line Items]              
Notional amount | $     $ 20     $ 20  
Debt securities 2,264     2,411      
Certificates of deposit              
Debt Securities In Issue [Line Items]              
Debt securities 2,511     1,607      
Credit linked notes              
Debt Securities In Issue [Line Items]              
Credit linked notes 705     635      
Securitisation programmes              
Debt Securities In Issue [Line Items]              
Debt securities £ 7,271     £ 5,638