Fair value measurements and valuation processes - additional information (Details) - GBP (£) £ in Millions |
Jun. 30, 2025 |
Dec. 31, 2024 |
Jun. 30, 2024 |
|---|---|---|---|
| At fair value | |||
| Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items] | |||
| Borrowings | £ 33,495 | £ 34,596 | £ 37,031 |
| Level 1 | |||
| Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items] | |||
| Assets at fair value | 1,069 | 447 | 583 |
| Level 3 | |||
| Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items] | |||
| Assets at fair value | £ 157 | £ 212 | £ 235 |