Retirement Benefit Schemes - Schedule of Net Liabilities of Funded Pension Schemes by Territory (Details) - GBP (£) £ in Millions	Dec. 31, 2024	Dec. 31, 2023
Disclosure Of Net Defined Benefit Liability Asset [Line Items]
Present value of funded/unfunded scheme liabilities	£ (6,439)	£ (7,202)
Fair value of funded scheme assets	6,612	7,317
Surplus (deficit) in funded plans excluding unrecognised scheme surpluses	907	900
Funded defined benefit plans
Disclosure Of Net Defined Benefit Liability Asset [Line Items]
Present value of funded/unfunded scheme liabilities	(5,705)	(6,417)
Fair value of funded scheme assets	6,612	7,317
Pension schemes
Disclosure Of Net Defined Benefit Liability Asset [Line Items]
Present value of funded/unfunded scheme liabilities	(5,918)	(6,647)
Surplus (deficit) in funded plans excluding unrecognised scheme surpluses	912	905
Pension schemes \| Funded defined benefit plans
Disclosure Of Net Defined Benefit Liability Asset [Line Items]
Present value of funded/unfunded scheme liabilities	(5,560)	(6,267)
Fair value of funded scheme assets	6,472	7,172
Surplus (deficit) in funded plans excluding unrecognised scheme surpluses	912	905
Pension schemes \| United States
Disclosure Of Net Defined Benefit Liability Asset [Line Items]
Present value of funded/unfunded scheme liabilities	(1,380)	(1,439)
Fair value of funded scheme assets	1,843	1,890
Surplus (deficit) in funded plans excluding unrecognised scheme surpluses	463	451
Pension schemes \| United Kingdom
Disclosure Of Net Defined Benefit Liability Asset [Line Items]
Present value of funded/unfunded scheme liabilities	(1,942)	(2,132)
Fair value of funded scheme assets	2,109	2,315
Surplus (deficit) in funded plans excluding unrecognised scheme surpluses	167	183
Pension schemes \| Germany
Disclosure Of Net Defined Benefit Liability Asset [Line Items]
Present value of funded/unfunded scheme liabilities	(695)	(741)
Fair value of funded scheme assets	798	863
Surplus (deficit) in funded plans excluding unrecognised scheme surpluses	103	122
Pension schemes \| Canada
Disclosure Of Net Defined Benefit Liability Asset [Line Items]
Present value of funded/unfunded scheme liabilities	(499)	(556)
Fair value of funded scheme assets	534	594
Surplus (deficit) in funded plans excluding unrecognised scheme surpluses	35	38
Pension schemes \| Netherlands
Disclosure Of Net Defined Benefit Liability Asset [Line Items]
Present value of funded/unfunded scheme liabilities	(465)	(736)
Fair value of funded scheme assets	542	780
Surplus (deficit) in funded plans excluding unrecognised scheme surpluses	77	44
Pension schemes \| Switzerland
Disclosure Of Net Defined Benefit Liability Asset [Line Items]
Present value of funded/unfunded scheme liabilities	(243)	(273)
Fair value of funded scheme assets	267	295
Surplus (deficit) in funded plans excluding unrecognised scheme surpluses	24	22
Pension schemes \| Rest of Group
Disclosure Of Net Defined Benefit Liability Asset [Line Items]
Present value of funded/unfunded scheme liabilities	(336)	(390)
Fair value of funded scheme assets	379	435
Surplus (deficit) in funded plans excluding unrecognised scheme surpluses	£ 43	£ 45

Surplus (deficit) in funded plans excluding unrecognised scheme surpluses.

No definition available.

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- Definition

The present value, without deducting any plan assets, of expected future payments required to settle the obligation resulting from employee service in the current and prior periods. [Refer: Plan assets, at fair value]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 57
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_57_a&doctype=Standard
-URIDate 2024-03-27

+ Details

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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.

+ References

No definition available.

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- Definition

The fair value of defined benefit plan assets. Plan assets comprise assets held by a long-term employee benefit fund and qualifying insurance policies. [Refer: At fair value [member]]

+ References

+ Details

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