Earnings per share - Summary of adjusted earnings per share (Detail) - GBP (£) £ / shares in Units, £ in Millions, shares in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Earnings per share
Adjusted net profit attributable to shareholders	£ 2,156	£ 1,961	£ 1,689	£ 1,543	£ 1,808
Weighted average number of shares	1,891.8	1,918.5	1,928.0
Adjusted EPS	£ 1.140	£ 1.022	£ 0.876	£ 0.801	£ 0.930

The number of ordinary shares outstanding at the beginning of the period, adjusted by the number of ordinary shares bought back or issued during the period multiplied by a time-weighting factor.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 33
-IssueDate 2023-01-01
-Paragraph 70
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=33&code=ifrs-tx-2023-en-r&anchor=para_70_b&doctype=Standard
-URIDate 2023-03-23

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration