v3.26.1
Share capital - Narrative (Details) - GBP (£)
£ / shares in Units, £ in Millions
 1 Months Ended 12 Months Ended
Jun. 30, 2024
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Disclosure of classes of share capital [abstract]        
Par value per share (GBP per share)   £ 0.1243129    
Number of ordinary shares per ADS (in shares)   5    
Proceeds from issuing shares   £ 2 £ 5  
Amount of unclaimed dividends derecognised   1 3  
Net proceeds from issue of ordinary shares £ 6,839      
Transaction fees related to Rights Issue £ 162 £ 0 £ 162 £ 0
Increase (decrease) In number of Rights Issued (in shares) 1,085,000,000      
Issue price (in GBP per share) £ 6.45      
Shares issued, number of ordinary shares, basis (in shares) 7      
Shares issued, number of ordinary shares, existing shares (in shares) 24      
Discount of issue price, percentage 33.00%      
Treasury stock (in shares)   226,000,000 235,000,000  
Treasury shares, market value   £ 2,863 £ 2,377  
Treasury shares, gifted (in shares)   5,000,000 9,000,000  
Treasury stock, reissued (in shares)   5,000,000 3,000,000  
Shares reissued to employee share schemes as percent of ordinary shares   0.20% 0.20%  
Treasury shares, reissued, nominal value   £ 1 £ 1  
Gross proceeds from reissue of treasury shares   40 18  
Purchase of own shares, employee share trusts   £ 3 £ 11  
Maximum number of treasury shares held during the year (in shares)   235,000,000 247,000,000  
Treasury shares as percent of ordinary shares   4.50% 4.80%  
Treasury shares, nominal value   £ 29 £ 31