Fair values of financial assets and liabilities - Schedule of Valuation Adjustments (Details) - GBP (£) £ in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| FINANCIAL INSTRUMENTS (Details) - Schedule of Valuation Adjustments [Line Items] | ||
| Valuation adjustment | £ 144 | £ 190 |
| Credit Valuation Adjustment | ||
| FINANCIAL INSTRUMENTS (Details) - Schedule of Valuation Adjustments [Line Items] | ||
| Valuation adjustment | 98 | 122 |
| Debit Valuation Adjustment | ||
| FINANCIAL INSTRUMENTS (Details) - Schedule of Valuation Adjustments [Line Items] | ||
| Valuation adjustment | (43) | (42) |
| Funding Valuation Adjustment | ||
| FINANCIAL INSTRUMENTS (Details) - Schedule of Valuation Adjustments [Line Items] | ||
| Valuation adjustment | 29 | 47 |
| Liquidity Adjustment | ||
| FINANCIAL INSTRUMENTS (Details) - Schedule of Valuation Adjustments [Line Items] | ||
| Valuation adjustment | 57 | 60 |
| Other | ||
| FINANCIAL INSTRUMENTS (Details) - Schedule of Valuation Adjustments [Line Items] | ||
| Valuation adjustment | £ 3 | £ 3 |