Operating Expenses - Summary of Services From the Group's Auditors (Detail) - GBP (£) £ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Auditors Remuneration [line items] | |||
| Total audit fees | £ 9 | £ 9 | £ 10 |
| Audit-related and other assurance services | 0 | 0 | 0 |
| Other non-audit services | 0 | 0 | 0 |
| Total other services | 0 | 0 | 0 |
| Total non-audit services | 0 | 0 | 0 |
| Total | 9 | 9 | 10 |
| Parent [member] | |||
| Auditors Remuneration [line items] | |||
| Total audit fees | 7 | 7 | 8 |
| Subsidiaries [member] | |||
| Auditors Remuneration [line items] | |||
| Total audit fees | £ 2 | £ 2 | £ 2 |