v3.26.1
Other equity instruments and own shares (Details) - EUR (€)
€ / shares in Units, € in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Sep. 08, 2017
Disclosure Of Other Equity Instruments And Own Shares [Line Items]          
Fidelity bonds, nominal value         € 981
Reserve of equity component of convertible instruments € 0 € 0 € 720   € 686
Equity € 112,748 € 107,327 € 104,241 € 97,585  
Share capital (in shares) 14,689,319,502 15,152,492,322 16,184,146,059 16,794,401,584  
Treasury shares, held by the group, as a percentage of issued share capital (in percentage) 0.075% 0.102% 1.84%    
Purchase of treasury shares (in shares) 584,363,745 930,610,636      
Average purchase price of bank shares (in euro per share) € 6.98 € 4.34      
Treasury shares, number of shares amortized (in shares) 463,172,820 1,031,653,737      
Treasury shares, number of shares transferred (in shares) 125,643,093 181,243,113      
Average selling price of bank shares (in euro per share) € 6.48 € 4.22      
Treasury shares, number of shares transferred through donations (in shares)   22,167,105      
Net profit from transaction with treasury shares € 34 € 8 € 13    
2023 Program, Second          
Disclosure Of Other Equity Instruments And Own Shares [Line Items]          
Purchase of treasury shares (in shares)   403,030,171      
2024 Program          
Disclosure Of Other Equity Instruments And Own Shares [Line Items]          
Purchase of treasury shares (in shares)   341,781,250      
2024 Program, Second          
Disclosure Of Other Equity Instruments And Own Shares [Line Items]          
Purchase of treasury shares (in shares) 267,166,950        
2025 Program          
Disclosure Of Other Equity Instruments And Own Shares [Line Items]          
Purchase of treasury shares (in shares) 196,005,870        
Other equity instruments          
Disclosure Of Other Equity Instruments And Own Shares [Line Items]          
Equity € 273 € 217 195 € 175  
(-) Own shares          
Disclosure Of Other Equity Instruments And Own Shares [Line Items]          
Equity € (96) € (68) € (1,078) € (675)  
Share capital (in shares) 11,077,291 15,529,459 297,815,673