v3.26.1
Legal, competition and regulatory matters (Details)
£ in Millions, $ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Jul. 02, 2026
challenge
Mar. 31, 2026
GBP (£)
Jun. 30, 2026
GBP (£)
lawsuit
plaintiff
bank
Dec. 31, 2024
subsidiarie
Dec. 31, 2018
GBP (£)
Dec. 31, 2008
USD ($)
Dec. 31, 2025
GBP (£)
Disclosure of contingent liabilities [line items]              
Provisions | £     £ 723       £ 766
Civil actions in respect of USD LIBOR              
Disclosure of contingent liabilities [line items]              
Number of lawsuits with damages sought     1        
Civil Actions In Respect Of VRDO - Private Plaintiffs              
Disclosure of contingent liabilities [line items]              
Number of lawsuits with damages sought     3        
Civil actions in respect of the US anti-terrorism act              
Disclosure of contingent liabilities [line items]              
Number of lawsuits with damages sought     8        
Number of plaintiffs | plaintiff     4,000        
Civil actions in respect of the US anti-terrorism act - EDNY              
Disclosure of contingent liabilities [line items]              
Number of lawsuits with damages sought     6        
Number of lawsuits dismissed     3        
Number of lawsuits subject to appeal     1        
Number of lawsuits consolidated into a separate lawsuit     2        
Number of separate lawsuits     1        
Number of initial lawsuits amended     1        
Number of banks claims against | bank     1        
Civil actions in respect of the US anti-terrorism act - SDNY              
Disclosure of contingent liabilities [line items]              
Number of lawsuits with damages sought     2        
HMRC assessments concerning UK VAT              
Disclosure of contingent liabilities [line items]              
Loss contingency, damages sought, claimed amounts, value | £         £ 181    
HMRC assessments concerning UK VAT | Barclays UK PLC              
Disclosure of contingent liabilities [line items]              
Loss contingency, damages sought, claimed amounts, value | £         128    
HM Revenue and Customs (HMRC) assessments concerning UK Value Added Tax [member]              
Disclosure of contingent liabilities [line items]              
Number of overseas subsidiaries denied VAT Grouping by the HMRC | subsidiarie       1      
Motor finance commission arrangements              
Disclosure of contingent liabilities [line items]              
Increase (decrease) in other provisions | £   £ 105          
Provisions | £     £ 430       £ 325
Number of legal challenges | challenge 4            
Motor finance commission arrangements | Minimum              
Disclosure of contingent liabilities [line items]              
Compensatory interest     0.03        
Originated and sold to third parties by Acquired Subsidiary | RMBS repurchase requests | US residential and commercial mortgage-related activity and litigation              
Disclosure of contingent liabilities [line items]              
Number of lawsuits with damages sought     1        
Barclays Bank PLC | BDC Finance LLC              
Disclosure of contingent liabilities [line items]              
Litigation settlements approved, value | $           $ 298  
Barclays Bank PLC | HMRC assessments concerning UK VAT              
Disclosure of contingent liabilities [line items]              
Loss contingency, damages sought, claimed amounts, value | £         £ 53