Fair value measurements and valuation processes - additional information (Details) - GBP (£) £ in Millions |
Jun. 30, 2026 |
Dec. 31, 2025 |
Jun. 30, 2025 |
|---|---|---|---|
| At fair value | |||
| Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items] | |||
| Borrowings | £ 33,503 | £ 33,717 | £ 33,495 |
| Level 1 | |||
| Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items] | |||
| Assets at fair value | 203 | 211 | 1,069 |
| Level 3 | |||
| Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items] | |||
| Assets at fair value | £ 75 | £ 138 | £ 157 |