v3.25.2
Credit Risk - Disclosure of analysis of management value at risk (VaR) (Details) - GBP (£)
£ in Millions
Jun. 30, 2025
Dec. 31, 2024
Jun. 30, 2024
Average      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk £ 19 £ 24 £ 29
Average | Credit risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 16 20 22
Average | Interest rate risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 15 14 16
Average | Equity risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 8 5 6
Average | Basis risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 5 5 6
Average | Spread risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 5 4 5
Average | Foreign exchange risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 4 4 4
Average | Commodity risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 0 0 0
Average | Inflation risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 5 4 4
Average | Diversification effect      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk (39) (32) (34)
High      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 30 32 36
High | Credit risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 20 24 27
High | Interest rate risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 25 22 25
High | Equity risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 14 12 9
High | Basis risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 7 6 8
High | Spread risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 7 7 7
High | Foreign exchange risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 7 7 9
High | Commodity risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 1 1 1
High | Inflation risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 8 5 5
Low      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 10 15 20
Low | Credit risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 13 17 19
Low | Interest rate risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 5 7 9
Low | Equity risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 5 2 4
Low | Basis risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 4 4 4
Low | Spread risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 4 3 4
Low | Foreign exchange risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 3 3 2
Low | Commodity risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk 0 0 0
Low | Inflation risk      
Disclosure of nature and extent of risks arising from financial instruments [line items]      
Value at risk £ 3 £ 2 £ 2