Other financial assets (Details) - GBP (£) £ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Disclosure Of Detailed Information About Hedging Instruments LineItems
Other financial assets	£ 63,243	£ 51,102
Amount of shares acquired	0	0
Permanent TSB p.l.c.
Disclosure Of Detailed Information About Hedging Instruments LineItems
Disposal of shares		47
VISA
Disclosure Of Detailed Information About Hedging Instruments LineItems
Disposal of shares	62	0
UBS Equity Funds
Disclosure Of Detailed Information About Hedging Instruments LineItems
Disposal of shares		35
All categories other than held for trading
Disclosure Of Detailed Information About Hedging Instruments LineItems
Other debt securities	33,921	28,754
Total securities	62,139	50,024
Equity shares	251	313
Loans classified as other financial assets	853	765
Other financial assets	63,243	51,102
All categories other than held for trading \| UNITED KINGDOM
Disclosure Of Detailed Information About Hedging Instruments LineItems
Central and local government debt securities	16,852	9,330
All categories other than held for trading \| UNITED STATES
Disclosure Of Detailed Information About Hedging Instruments LineItems
Central and local government debt securities	5,087	6,164
All categories other than held for trading \| Countries other than the US and the UK
Disclosure Of Detailed Information About Hedging Instruments LineItems
Central and local government debt securities	6,279	5,776
Mandatory fair value through profit or loss
Disclosure Of Detailed Information About Hedging Instruments LineItems
Other debt securities	1	1
Total securities	1	1
Equity shares	4	2
Loans classified as other financial assets	793	700
Other financial assets	798	703
Designated at fair value
Disclosure Of Detailed Information About Hedging Instruments LineItems
Other debt securities	3	2
Total securities	5	5
Other financial assets	5	5
Designated at fair value \| Countries other than the US and the UK
Disclosure Of Detailed Information About Hedging Instruments LineItems
Central and local government debt securities	2	3
Fair value through other comprehensive income
Disclosure Of Detailed Information About Hedging Instruments LineItems
Other debt securities	13,476	10,627
Total securities	37,536	28,323
Equity shares	247	311
Loans classified as other financial assets	60	65
Other financial assets	37,843	28,699
Fair value through other comprehensive income \| UNITED KINGDOM
Disclosure Of Detailed Information About Hedging Instruments LineItems
Central and local government debt securities	13,281	6,441
Fair value through other comprehensive income \| UNITED STATES
Disclosure Of Detailed Information About Hedging Instruments LineItems
Central and local government debt securities	4,587	5,517
Fair value through other comprehensive income \| Countries other than the US and the UK
Disclosure Of Detailed Information About Hedging Instruments LineItems
Central and local government debt securities	6,192	5,738
Amortised cost
Disclosure Of Detailed Information About Hedging Instruments LineItems
Other debt securities	20,441	18,124
Total securities	24,597	21,695
Other financial assets	24,597	21,695
Amortised cost \| UNITED KINGDOM
Disclosure Of Detailed Information About Hedging Instruments LineItems
Central and local government debt securities	3,571	2,889
Amortised cost \| UNITED STATES
Disclosure Of Detailed Information About Hedging Instruments LineItems
Central and local government debt securities	500	647
Amortised cost \| Countries other than the US and the UK
Disclosure Of Detailed Information About Hedging Instruments LineItems
Central and local government debt securities	£ 85	£ 35

The amount of instruments representing indebtedness, including instruments called debt securities, held by the entity.

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The amount of instruments held by the entity that provide evidence of a residual interest in the assets of another entity after deducting all of its liabilities.

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The amount of debt instruments, including instruments called debt securities, held by the entity that were issued by a government. [Refer: Debt instruments held; Government [member]]

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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The amount of debt instruments, including instruments called debt securities, held by the entity that it does not separately disclose in the same statement or note. [Refer: Debt instruments held]

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The amount of financial assets that the entity does not separately disclose in the same statement or note. [Refer: Financial assets]

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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The cash inflow from sales of investments other than investments accounted for using the equity method. [Refer: Investments accounted for using equity method; Investments other than investments accounted for using equity method]

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The cash outflow for the purchase of investments other than investments accounted for using equity method. [Refer: Investments accounted for using equity method; Investments other than investments accounted for using equity method]

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Loans classified as other financial assets

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