v3.26.1
Investments - Summary of financial information on the main associates and joint ventures (Details) - EUR (€)
€ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Disclosure of associates [line items]        
TOTAL ASSETS € 1,867,515 € 1,837,081 € 1,797,062  
TOTAL LIABILITIES 1,754,767 1,729,754 1,692,821  
Profit or loss for the year 15,500 13,744 12,183  
Other accumulated comprehensive income (37,974) (36,595) (35,020)  
Equity 112,748 107,327 104,241 € 97,585
TOTAL LIABILITIES AND EQUITY 1,867,515 1,837,081 1,797,062  
Profit (loss) from continuing operations 13,958 12,503 11,125  
Profit/(loss) after tax from discontinued operations 1,542 € 1,241 € 1,058  
Aggregate amounts for entities accounted for using the equity method | Merlin Properties, SOCIMI, S.A.        
Disclosure of associates [line items]        
Current assets 1,701      
Non current assets 11,758      
TOTAL ASSETS 13,459      
Current liabilities 840      
Non current liabilities 5,118      
TOTAL LIABILITIES 5,958      
Profit or loss for the year 284      
Other accumulated comprehensive income (11)      
Rest of equity 7,228      
Equity 7,501      
TOTAL LIABILITIES AND EQUITY 13,459      
Ordinary activities income 544      
Profit (loss) from continuing operations 284      
Profit/(loss) after tax from discontinued operations 0      
Aggregate amounts for entities accounted for using the equity method | Metrovacesa, S.A.        
Disclosure of associates [line items]        
Current assets 2,025      
Non current assets 389      
TOTAL ASSETS 2,414      
Current liabilities 507      
Non current liabilities 310      
TOTAL LIABILITIES 817      
Profit or loss for the year 16      
Other accumulated comprehensive income 0      
Rest of equity 1,581      
Equity 1,597      
TOTAL LIABILITIES AND EQUITY 2,414      
Ordinary activities income 658      
Profit (loss) from continuing operations 16      
Profit/(loss) after tax from discontinued operations 0      
Aggregate amounts for entities accounted for using the equity method | Pluxee Beneficios Brasil, S.A.        
Disclosure of associates [line items]        
Current assets 689      
Non current assets 652      
TOTAL ASSETS 1,341      
Current liabilities 254      
Non current liabilities 578      
TOTAL LIABILITIES 832      
Profit or loss for the year 87      
Other accumulated comprehensive income 0      
Rest of equity 422      
Equity 509      
TOTAL LIABILITIES AND EQUITY 1,341      
Ordinary activities income 457      
Profit (loss) from continuing operations 87      
Profit/(loss) after tax from discontinued operations 0      
Aggregate amounts for entities accounted for using the equity method | Zurich Santander Insurance America, S.L. - Consolidated        
Disclosure of associates [line items]        
Current assets 2,434      
Non current assets 20,190      
TOTAL ASSETS 22,624      
Current liabilities 657      
Non current liabilities 21,021      
TOTAL LIABILITIES 21,678      
Profit or loss for the year 534      
Other accumulated comprehensive income (33)      
Rest of equity 445      
Equity 946      
TOTAL LIABILITIES AND EQUITY 22,624      
Ordinary activities income 4,559      
Profit (loss) from continuing operations 534      
Profit/(loss) after tax from discontinued operations 0      
Aggregate amounts for entities accounted for using the equity method | CNP Santander        
Disclosure of associates [line items]        
Current assets 165      
Non current assets 2,139      
TOTAL ASSETS 2,304      
Current liabilities 186      
Non current liabilities 1,726      
TOTAL LIABILITIES 1,912      
Profit or loss for the year 101      
Other accumulated comprehensive income (9)      
Rest of equity 300      
Equity 392      
TOTAL LIABILITIES AND EQUITY 2,304      
Ordinary activities income 568      
Profit (loss) from continuing operations 101      
Profit/(loss) after tax from discontinued operations 0      
Aggregate amounts for entities accounted for using the equity method | Santander Caceis Latam Holding 1, S.L        
Disclosure of associates [line items]        
Current assets 201      
Non current assets 579      
TOTAL ASSETS 780      
Current liabilities 315      
Non current liabilities 35      
TOTAL LIABILITIES 350      
Profit or loss for the year 97      
Other accumulated comprehensive income 0      
Rest of equity 333      
Equity 430      
TOTAL LIABILITIES AND EQUITY 780      
Ordinary activities income 163      
Profit (loss) from continuing operations 97      
Profit/(loss) after tax from discontinued operations 0      
Aggregate amounts for entities accounted for using the equity method | U.C.I., S.A.        
Disclosure of associates [line items]        
Current assets 397      
Non current assets 8,876      
TOTAL ASSETS 9,273      
Current liabilities 6,930      
Non current liabilities 1,715      
TOTAL LIABILITIES 8,645      
Profit or loss for the year (75)      
Other accumulated comprehensive income 114      
Rest of equity 589      
Equity 628      
TOTAL LIABILITIES AND EQUITY 9,273      
Ordinary activities income 499      
Profit (loss) from continuing operations (75)      
Profit/(loss) after tax from discontinued operations 0      
Aggregate amounts for entities accounted for using the equity method | Hyundai Capital UK Limited        
Disclosure of associates [line items]        
Current assets 2,022      
Non current assets 3,665      
TOTAL ASSETS 5,687      
Current liabilities 3,685      
Non current liabilities 1,480      
TOTAL LIABILITIES 5,165      
Profit or loss for the year 77      
Other accumulated comprehensive income (1)      
Rest of equity 446      
Equity 522      
TOTAL LIABILITIES AND EQUITY 5,687      
Ordinary activities income 426      
Profit (loss) from continuing operations 77      
Profit/(loss) after tax from discontinued operations 0      
Aggregate amounts for entities accounted for using the equity method | Fortune Auto Finance Co., Ltd        
Disclosure of associates [line items]        
Current assets 167      
Non current assets 1,933      
TOTAL ASSETS 2,100      
Current liabilities 10      
Non current liabilities 1,627      
TOTAL LIABILITIES 1,637      
Profit or loss for the year 20      
Other accumulated comprehensive income 0      
Rest of equity 443      
Equity 463      
TOTAL LIABILITIES AND EQUITY 2,100      
Ordinary activities income 159      
Profit (loss) from continuing operations 20      
Profit/(loss) after tax from discontinued operations 0      
Aggregate amounts for entities accounted for using the equity method | Santander Seguros y Reaseguros, Compañía Aseguradora, S.A.        
Disclosure of associates [line items]        
Current assets 157      
Non current assets 1,710      
TOTAL ASSETS 1,867      
Current liabilities 140      
Non current liabilities 1,243      
TOTAL LIABILITIES 1,383      
Profit or loss for the year 145      
Other accumulated comprehensive income (21)      
Rest of equity 360      
Equity 484      
TOTAL LIABILITIES AND EQUITY 1,867      
Ordinary activities income 907      
Profit (loss) from continuing operations 145      
Profit/(loss) after tax from discontinued operations 0      
Aggregate amounts for entities accounted for using the equity method | Banco RCI Brasil S.A.        
Disclosure of associates [line items]        
Current assets 10      
Non current assets 2,221      
TOTAL ASSETS 2,231      
Current liabilities 112      
Non current liabilities 1,924      
TOTAL LIABILITIES 2,036      
Profit or loss for the year 54      
Other accumulated comprehensive income 4      
Rest of equity 137      
Equity 195      
TOTAL LIABILITIES AND EQUITY 2,231      
Ordinary activities income 312      
Profit (loss) from continuing operations 54      
Profit/(loss) after tax from discontinued operations € 0