v3.26.1
Fair values of financial assets and liabilities - Schedule of Sensitivity of Level 3 Valuations (Details) - Level 3 - Recurring fair value measurement - GBP (£)
£ in Millions
 6 Months Ended 12 Months Ended
Jun. 30, 2026
Dec. 31, 2025
Credit spreads | Financial liabilities at fair value through profit or loss | Securitisation notes and other    
Increase (decrease) in fair value measurement for sensitivity analyses in which inputs are changed individually, liabilities [abstract]    
Max up 0.50% 0.50%
Max down (0.50%) (0.50%)
Favourable changes £m £ 1 £ 1
Unfavourable changes £m £ (1) £ (1)
HPI growth | Derivative financial liabilities | Shared appreciation rights    
Increase (decrease) in fair value measurement for sensitivity analyses in which inputs are changed individually, liabilities [abstract]    
Max up 1.00% 1.00%
Max down (1.00%) (1.00%)
Favourable changes £m £ 9 £ 11
Unfavourable changes £m £ (8) £ (10)
Interest rate ATM volatility | Derivative financial liabilities | Interest rate derivatives    
Increase (decrease) in fair value measurement for sensitivity analyses in which inputs are changed individually, liabilities [abstract]    
Max up 0.04% 0.04%
Max down (0.04%) (0.04%)
Favourable changes £m £ 6 £ 4
Unfavourable changes £m £ (5) £ (3)
Financial assets at fair value through profit or loss | Loans and advances to customers | Credit spreads    
Increase (decrease) in fair value measurement for sensitivity analyses in which inputs are changed individually, assets [abstract]    
Max up 1.50% 1.50%
Max down (1.15%) (1.15%)
Favourable changes £m £ 110 £ 155
Unfavourable changes £m £ (114) £ (147)
Financial assets at fair value through profit or loss | Loans and advances to customers | HPI growth    
Increase (decrease) in fair value measurement for sensitivity analyses in which inputs are changed individually, assets [abstract]    
Max up 1.00% 1.00%
Max down (1.00%) (1.00%)
Favourable changes £m £ 11 £ 13
Unfavourable changes £m £ (10) £ (12)
Financial assets at fair value through profit or loss | Debt securities | Credit spreads    
Increase (decrease) in fair value measurement for sensitivity analyses in which inputs are changed individually, assets [abstract]    
Max up 0.52% 2.10%
Max down (0.85%) (0.50%)
Favourable changes £m £ 35 £ 56
Unfavourable changes £m £ (27) £ (53)
Financial assets at fair value through profit or loss | Debt securities | Earnings multiple    
Increase (decrease) in fair value measurement for sensitivity analyses in which inputs are changed individually, assets [abstract]    
Max up 10.00% 10.00%
Max down (10.00%) (10.00%)
Favourable changes £m £ 36 £ 86
Unfavourable changes £m £ (36) £ (86)
Financial assets at fair value through profit or loss | Equity shares | Price    
Increase (decrease) in fair value measurement for sensitivity analyses in which inputs are changed individually, assets [abstract]    
Max up 46.00% 31.00%
Max down (46.00%) (31.00%)
Favourable changes £m £ 85 £ 86
Unfavourable changes £m £ (89) £ (89)
Financial assets at fair value through profit or loss | Equity shares | Earnings multiple    
Increase (decrease) in fair value measurement for sensitivity analyses in which inputs are changed individually, assets [abstract]    
Max up 10.00% 10.00%
Max down (10.00%) (10.00%)
Favourable changes £m £ 7 £ 17
Unfavourable changes £m £ (7) £ (17)
Financial assets at fair value through other comprehensive income | Debt securities | Credit spreads    
Increase (decrease) in fair value measurement for sensitivity analyses in which inputs are changed individually, assets [abstract]    
Max up 0.75% 0.75%
Max down (0.75%) (0.75%)
Favourable changes £m £ 1 £ 2
Unfavourable changes £m £ (1) £ (2)
Financial assets at fair value through other comprehensive income | Equity shares | Price    
Increase (decrease) in fair value measurement for sensitivity analyses in which inputs are changed individually, assets [abstract]    
Max up 20.00% 20.00%
Max down (20.00%) (20.00%)
Favourable changes £m £ 5 £ 3
Unfavourable changes £m £ (5) £ (3)
Derivative financial liabilities | Interest rate derivatives | Interest rate ATM volatility    
Increase (decrease) in fair value measurement for sensitivity analyses in which inputs are changed individually, assets [abstract]    
Max up 0.04% 0.04%
Max down (0.04%) (0.04%)
Favourable changes £m £ 5 £ 4
Unfavourable changes £m £ (5) £ (4)
Derivative financial liabilities | Interest rate derivatives | Uncertainty of recovery rates    
Increase (decrease) in fair value measurement for sensitivity analyses in which inputs are changed individually, assets [abstract]    
Max up 8.00% 8.00%
Max down (8.00%) (8.00%)
Favourable changes £m £ 21 £ 21
Unfavourable changes £m £ (21) £ (21)