Financial Liabilities - Borrowings - Summary of Carrying Amounts of Borrowings which Denominated in Currencies (Detail) - GBP (£) £ in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Disclosure of detailed information about borrowings [line items] | ||
| Borrowings | £ 1,481 | £ 1,472 |
| US Dollars [member] | ||
| Disclosure of detailed information about borrowings [line items] | ||
| Borrowings | 153 | 187 |
| Sterling [member] | ||
| Disclosure of detailed information about borrowings [line items] | ||
| Borrowings | 1,309 | 1,013 |
| Euro [member] | ||
| Disclosure of detailed information about borrowings [line items] | ||
| Borrowings | 2 | 253 |
| Other currency [member] | ||
| Disclosure of detailed information about borrowings [line items] | ||
| Borrowings | £ 17 | £ 19 |