Exchange rates -Summary of Foreign Exchange Rate (Detail)	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Sterling
Disclosure of exchange rates [line items]
Average	0.76	0.78	0.80
Closing	0.74	0.80	0.78
Euro
Disclosure of exchange rates [line items]
Average	0.89	0.92	0.92
Closing	0.85	0.96	0.90

The spot exchange rate at the end of the reporting period. Exchange rate is the ratio of exchange for two currencies. Spot exchange rate is the exchange rate for immediate delivery.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Note Expiry date 2027-01-01
-Name IAS
-Number 1
-IssueDate 2025-01-01
-Paragraph 112
-Subparagraph c
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2025-en-b&anchor=para_112_c&doctype=Standard
-URIDate 2025-03-27

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant