Share Capital and Share Premium - Additional Information (Detail) - GBP (£) £ / shares in Units, £ in Millions, shares in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Feb. 27, 2025 |
|
| Disclosure of classes of share capital [line items] | |||
| Par value per share | £ 0.25 | £ 0.25 | |
| Number of shares repurchased | 32 | 32 | |
| Value of shares repurchased and cancelled | £ 352 | £ 318 | |
| Stock Repurchase Program, Remaining Authorized Repurchase Amount | 0 | 0 | |
| Non-adjusting Events After Reporting Period [Member] | |||
| Disclosure of classes of share capital [line items] | |||
| Amount of shares authorized for repurchase | £ 350 | ||
| Capital redemption reserve [member] | |||
| Disclosure of classes of share capital [line items] | |||
| Reduction of issued capital | £ 8 | £ 8 | |