Earnings Per Share - Summary of 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
Earnings per share [abstract]
Earnings for the year	£ 380	£ 244	£ 178
Non-controlling interest	(2)	(2)	(1)
Earnings attributable to equity shareholders	£ 378	£ 242	£ 177
Weighted average number of shares (millions)	711.5	738.1	754.1
Effect of dilutive share options (millions)	5.8	3.9	5.0
Weighted average number of shares (millions) for diluted earnings	717.3	742.0	759.1
Earnings per share (in pence per share)
Basic	£ 0.531	£ 0.328	£ 0.235
Diluted	£ 0.527	£ 0.326	£ 0.233

The weighted average number of ordinary shares outstanding plus the weighted average number of ordinary shares that would be issued on the conversion of all the dilutive potential ordinary shares into ordinary shares. [Refer: Ordinary shares [member]; Weighted average [member]]

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The amount of profit (loss) attributable to ordinary equity holders of the parent entity (the numerator) divided by the weighted average number of ordinary shares outstanding during the period (the denominator).

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The amount of profit (loss) attributable to ordinary equity holders of the parent entity (the numerator), divided by the weighted average number of ordinary shares outstanding during the period (the denominator), both adjusted for the effects of all dilutive potential ordinary shares. [Refer: Ordinary shares [member]; Weighted average [member]]

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The potential dilutive effect on the weighted average number of ordinary shares that relate to the assumed exercise of the entity's share options.

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The profit (loss) from continuing and discontinued operations attributable to non-controlling interests. [Refer: Profit (loss); Non-controlling interests]

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The profit (loss) from continuing and discontinued operations attributable to owners of the parent. [Refer: Profit (loss)]

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The profit (loss) from continuing operations. [Refer: Continuing operations [member]; Profit (loss)]

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