v3.26.1
ACQUISITION OF TSB - Additional Information (Details) - GBP (£)
£ in Millions
 2 Months Ended 3 Months Ended 6 Months Ended
Apr. 30, 2026
Jun. 30, 2026
Mar. 31, 2026
Jun. 30, 2026
Dec. 31, 2025
Disclosure of detailed information about business combination [line items]          
Subordinated liabilities   £ 2,552   £ 2,552 £ 2,032
Debt securities in issue   £ 47,255   £ 47,255 £ 41,388
Retail deposit funding, percentage   80.00%   80.00%  
Wholesale debt funding, percentage   20.00%   20.00%  
Pre acquisition costs recognised as expense     £ 25    
Funding spread assumption          
Disclosure of detailed information about business combination [line items]          
Significant unobservable input, assets   0.0110   0.0110  
Sensitivity analysis for fair value measurement reasonably possible change       0.25%  
Funding spread assumption | Minimum          
Disclosure of detailed information about business combination [line items]          
Significant unobservable input, assets   0.0090   0.0090  
Funding spread assumption | Maximum          
Disclosure of detailed information about business combination [line items]          
Significant unobservable input, assets   0.0130   0.0130  
TSB          
Disclosure of detailed information about business combination [line items]          
Percentage of voting equity interests acquired 100.00%        
Consideration paid (received) £ 2,650        
Consideration paid (received), TNAV variation 213        
Goodwill arising on acquisition 669        
Technology-based intangible assets recognised as of acquisition date 0        
Fair value of acquired receivables 35,983        
Gross contractual amounts receivable for acquired receivables 36,184        
Best estimate at acquisition date of contractual cash flows not expected to be collected for acquired receivables 201        
Acquisition-related costs recognised as expense for transaction recognised separately from acquisition of assets and assumption of liabilities in business combination 85        
Post acquisition integration costs recognised in operating expenses       £ 44  
Revenue of acquiree since acquisition date   £ 200      
Profit before tax of acquiree since acquisition date   (25)      
Profit (loss) of acquiree since acquisition date   £ (21)      
Revenue of combined entity as if combination occurred at beginning of period       2,877  
Profit (loss) of combined entity as if combination occurred at beginning of period       £ 445  
TSB | FV Adjustments          
Disclosure of detailed information about business combination [line items]          
Goodwill arising on acquisition 0        
Intangible assets 246        
Mortgage loans 229        
TSB | Carrying amount          
Disclosure of detailed information about business combination [line items]          
Goodwill arising on acquisition 0        
Intangible assets 123        
TSB | Brand names          
Disclosure of detailed information about business combination [line items]          
Customer-related intangible assets recognised as of acquisition date 29        
TSB | Core deposit intangibles          
Disclosure of detailed information about business combination [line items]          
Customer-related intangible assets recognised as of acquisition date £ 294        
Useful life measured as period of time, intangible assets other than goodwill 5 years        
TSB | Core deposit intangibles | FV Adjustments          
Disclosure of detailed information about business combination [line items]          
Customer-related intangible assets recognised as of acquisition date £ 294        
TSB | Purchased credit card receivables (PCCR)          
Disclosure of detailed information about business combination [line items]          
Customer-related intangible assets recognised as of acquisition date £ 16        
Useful life measured as period of time, intangible assets other than goodwill 3 years        
TSB | Computer software | FV Adjustments          
Disclosure of detailed information about business combination [line items]          
Intangible assets £ (92)        
TSB | Computer software | Carrying amount          
Disclosure of detailed information about business combination [line items]          
Intangible assets 123        
TSB | AT1 Securities          
Disclosure of detailed information about business combination [line items]          
Consideration paid (received) 255        
TSB | Debt securities          
Disclosure of detailed information about business combination [line items]          
Consideration paid (received) 962        
TSB | Fixed-to-floating rate callable subordinated Tier 2 capital notes          
Disclosure of detailed information about business combination [line items]          
Subordinated liabilities 300        
TSB | Senior unsecured debt securities          
Disclosure of detailed information about business combination [line items]          
Debt securities in issue £ 650