v3.25.2
Fair values of financial instruments carried at fair value - Financial instruments carried at fair value and bases of valuation (Details) - GBP (£)
£ in Millions
Jun. 30, 2025
Dec. 31, 2024
Jun. 30, 2024
Dec. 31, 2023
Trading liabilities | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities £ 0    
Financial liabilities designated at fair value | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 10 104    
Derivatives | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 9 15    
Trading assets | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 0 0    
Financial assets designated and otherwise mandatorily measured at fair value through profit or loss | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 12,389 11,607    
Derivatives | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 37 29    
Financial investments | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 11,574 6,776    
Recurring fair value measurements | Level 3        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 6,091 7,613    
Financial liabilities 5,847 5,941    
Recurring fair value measurements | Trading liabilities        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 39,542 42,633    
Recurring fair value measurements | Trading liabilities | Level 1        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 25,862 24,713    
Recurring fair value measurements | Trading liabilities | Level 1 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 0    
Recurring fair value measurements | Trading liabilities | Level 2        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 13,646 17,296    
Recurring fair value measurements | Trading liabilities | Level 2 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 0    
Recurring fair value measurements | Trading liabilities | Level 3        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 34 624 £ 102 £ 252
Recurring fair value measurements | Trading liabilities | Level 3 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 0    
Recurring fair value measurements | Financial liabilities designated at fair value        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 39,964 37,443    
Recurring fair value measurements | Financial liabilities designated at fair value | Level 1        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 1,074 1,078    
Recurring fair value measurements | Financial liabilities designated at fair value | Level 1 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 0 0    
Recurring fair value measurements | Financial liabilities designated at fair value | Level 2        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 35,852 33,403    
Recurring fair value measurements | Financial liabilities designated at fair value | Level 2 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 10 104    
Recurring fair value measurements | Financial liabilities designated at fair value | Level 3        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 3,038 2,962 3,846 3,958
Recurring fair value measurements | Financial liabilities designated at fair value | Level 3 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 0 0    
Recurring fair value measurements | Derivatives        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 176,367 197,082    
Recurring fair value measurements | Derivatives | Level 1        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 1,443 745    
Recurring fair value measurements | Derivatives | Level 1 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 0 0    
Recurring fair value measurements | Derivatives | Level 2        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 172,149 193,982    
Recurring fair value measurements | Derivatives | Level 2 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 9 15    
Recurring fair value measurements | Derivatives | Level 3        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 2,775 2,355 2,956 2,335
Recurring fair value measurements | Derivatives | Level 3 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial liabilities 0 0    
Recurring fair value measurements | Trading assets        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 114,445 116,042    
Recurring fair value measurements | Trading assets | Level 1        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 84,862 87,915    
Recurring fair value measurements | Trading assets | Level 1 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 0 0    
Recurring fair value measurements | Trading assets | Level 2        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 27,048 24,557    
Recurring fair value measurements | Trading assets | Level 2 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 0 0    
Recurring fair value measurements | Trading assets | Level 3        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 2,535 3,570 2,102 2,050
Recurring fair value measurements | Trading assets | Level 3 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 0 0    
Recurring fair value measurements | Financial assets designated and otherwise mandatorily measured at fair value through profit or loss        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 9,097 9,417    
Recurring fair value measurements | Financial assets designated and otherwise mandatorily measured at fair value through profit or loss | Level 1        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 4,904 4,615    
Recurring fair value measurements | Financial assets designated and otherwise mandatorily measured at fair value through profit or loss | Level 1 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 2,234 2,365    
Recurring fair value measurements | Financial assets designated and otherwise mandatorily measured at fair value through profit or loss | Level 2        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 3,088 3,720    
Recurring fair value measurements | Financial assets designated and otherwise mandatorily measured at fair value through profit or loss | Level 2 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 8,209 7,189    
Recurring fair value measurements | Financial assets designated and otherwise mandatorily measured at fair value through profit or loss | Level 3        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 1,105 1,082 3,214 2,882
Recurring fair value measurements | Financial assets designated and otherwise mandatorily measured at fair value through profit or loss | Level 3 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 1,946 2,053    
Recurring fair value measurements | Derivatives        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 176,838 198,172    
Recurring fair value measurements | Derivatives | Level 1        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 832 1,219    
Recurring fair value measurements | Derivatives | Level 1 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 0 0    
Recurring fair value measurements | Derivatives | Level 2        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 173,737 195,071    
Recurring fair value measurements | Derivatives | Level 2 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 37 29    
Recurring fair value measurements | Derivatives | Level 3        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 2,269 1,882 2,496 1,823
Recurring fair value measurements | Derivatives | Level 3 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 0 0    
Recurring fair value measurements | Financial investments        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 41,097 39,990    
Recurring fair value measurements | Financial investments | Level 1        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 32,713 31,769    
Recurring fair value measurements | Financial investments | Level 1 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 2,331 2,113    
Recurring fair value measurements | Financial investments | Level 2        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 8,202 7,142    
Recurring fair value measurements | Financial investments | Level 2 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 8,870 4,261    
Recurring fair value measurements | Financial investments | Level 3        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets 182 1,079 £ 788 £ 907
Recurring fair value measurements | Financial investments | Level 3 | Disposal groups classified as held for sale        
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]        
Financial assets £ 373 £ 402