Earnings Per Share - Summary of Reconciliation from Basic to Diluted Earnings Per Share (Details) - GBP (£) £ / shares in Units, £ in Millions, shares in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Earnings per share [line items]
Price per ordinary shares (in GBP pence per share)	£ 0.25
Basic earnings/(loss) per share (ordinary shares of 25p each), Earnings	£ 3,026	£ (14,412)	£ 6,617
Diluted earnings/(loss) per share, Earnings	£ 3,026	£ (14,412)	£ 6,617
Basic earnings/(loss) per share (ordinary shares of 25p each), Weighted average number of shares (in shares)	2,214	2,229	2,256
Share options, Weighted average number of shares (in shares)	11	0	11
Diluted earnings/(loss) per share, Weighted average number of shares (in shares)	2,225	2,229	2,267
Basic earnings/(loss) per share (in GBP per share)	£ 1.367	£ (6.466)	£ 2.933
Share options (in GBP pence per share)	(0.007)	0	(0.014)
Diluted earnings/(loss) per share (in GBP per share)	£ 1.360	£ (6.466)	£ 2.919
Share options
Earnings per share [line items]
Number of shares that are antidilutive in period presented (in shares)		8

Share options earnings (loss) per share.

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- Definition

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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- Definition

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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- Definition

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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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table.

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Number of (units of) instruments that are antidilutive in the period presented.

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- Definition

The nominal value per share.

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- Definition

The profit (loss) attributable to ordinary equity holders of the parent entity. [Refer: Profit (loss)]

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- Definition

The profit (loss) attributable to ordinary equity holders of the parent entity, adjusted for the effects of all dilutive potential ordinary shares. [Refer: Profit (loss)]

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- Definition

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.

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