v3.25.4
Risk Management - Disclosure of management Value at Risk (Details) - GBP (£)
£ in Millions
Dec. 31, 2025
Dec. 31, 2024
Average    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk £ 18 £ 26
High    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 31 36
Low    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 9 15
Credit risk | Average    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 15 21
Credit risk | High    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 21 27
Credit risk | Low    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 11 17
Interest rate risk | Average    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 15 15
Interest rate risk | High    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 25 25
Interest rate risk | Low    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 5 6
Equity risk | Average    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 7 6
Equity risk | High    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 14 12
Equity risk | Low    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 4 2
Basis risk | Average    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 6 5
Basis risk | High    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 9 8
Basis risk | Low    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 4 4
Spread risk | Average    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 5 5
Spread risk | High    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 7 7
Spread risk | Low    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 3 3
Foreign exchange risk | Average    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 4 4
Foreign exchange risk | High    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 7 9
Foreign exchange risk | Low    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 2 2
Commodity risk | Average    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 0 0
Commodity risk | High    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 1 1
Commodity risk | Low    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 0 0
Inflation risk | Average    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 5 4
Inflation risk | High    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 8 5
Inflation risk | Low    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk 3 2
Diversification effect | Average    
Disclosure of nature and extent of risks arising from financial instruments [line items]    
Value at risk £ (39) £ (34)