Derivative Financial Instruments and Hedge Accounting - Additional Information (Detail) - GBP (£) £ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
|
| Disclosure of detailed information about financial instruments [line items] | ||
| Reserve Of Gains And Losses On Hedging Instruments | £ 0 | £ 3 |
| Gross notional amounts | 1,531 | 3,130 |
| Fair value hedges [member] | ||
| Disclosure of detailed information about financial instruments [line items] | ||
| Financial instruments designated as hedging instruments, at fair value | 0 | |
| Hedges of net investment in foreign operations [member] | ||
| Disclosure of detailed information about financial instruments [line items] | ||
| Net movement on hedging instrument in fair value hedges | ||
| Collars [Member] | ||
| Disclosure of detailed information about financial instruments [line items] | ||
| Gross notional amounts | 334 | 180 |
| Forward And Swaps [Member] | ||
| Disclosure of detailed information about financial instruments [line items] | ||
| Gross notional amounts | £ 324 | £ 690 |