Dividends - Summary of Dividends Declared (Detail) - GBP (£) £ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Disclosure of dividends [line items]
Dividends paid	£ 160	£ 156	£ 155
Final dividend [member]
Disclosure of dividends [line items]
Dividends paid	110	107	106
Interim dividend [member]
Disclosure of dividends [line items]
Dividends paid	£ 50	£ 49	£ 49

The amount of dividends paid by the entity on ordinary shares. [Refer: Ordinary shares [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2027-01-01
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration