v3.26.1
Additional disclosure requirements - Schedule of preference shares and preferred securities by issuer (Details)
€ in Millions, £ in Millions, $ in Millions
 6 Months Ended
Jun. 30, 2026
EUR (€)
Jun. 30, 2026
GBP (£)
Jun. 30, 2026
USD ($)
Santander UK plc, October 1995 | Preference shares      
Disclosure of detailed information about financial instruments [line items]      
Outstanding issue amount | £   £ 80.3  
Interest rate 10.375% 10.375% 10.375%
Santander UK plc, February 1996 | Preference shares      
Disclosure of detailed information about financial instruments [line items]      
Outstanding issue amount | £   £ 80.3  
Interest rate 10.375% 10.375% 10.375%
Banco Santander, S.A., May 2021 | US Dollar      
Disclosure of detailed information about financial instruments [line items]      
Initial interest rate term 6 years    
Reprice term 5 years    
Subordinated issue, UST rate term 5 years    
Banco Santander, S.A., May 2021 | Euro      
Disclosure of detailed information about financial instruments [line items]      
Initial interest rate term 7 years    
Reprice term 5 years    
Subordinated issue, mid-swap rate term 5 years    
Banco Santander, S.A., May 2021 | Preferred securities | US Dollar      
Disclosure of detailed information about financial instruments [line items]      
Interest rate 4.75% 4.75% 4.75%
Adjustment to reference rate, after initial interest rate period 3.753% 3.753% 3.753%
Banco Santander, S.A., May 2021 | Preferred securities | Euro      
Disclosure of detailed information about financial instruments [line items]      
Interest rate 4.125% 4.125% 4.125%
Adjustment to reference rate, after initial interest rate period 4.311% 4.311% 4.311%
Banco Santander, S.A., May 2021 | Fixed interest rate | Preferred securities | US Dollar      
Disclosure of detailed information about financial instruments [line items]      
Outstanding issue amount | $     $ 298.3
Interest rate 4.75% 4.75% 4.75%
Banco Santander, S.A., May 2021 | Fixed interest rate | Preferred securities | Euro      
Disclosure of detailed information about financial instruments [line items]      
Outstanding issue amount | € € 750.0    
Interest rate 4.125% 4.125% 4.125%
Banco Santander, S.A., September 2021 | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Interest rate 3.625% 3.625% 3.625%
Initial interest rate term 8 years    
Reprice term 5 years    
Subordinated issue, mid-swap rate term 5 years    
Banco Santander, S.A., September 2021 | Fixed interest rate | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Outstanding issue amount | € € 1,000.0    
Interest rate 3.625% 3.625% 3.625%
Banco Santander, S.A., September 2021 | Mid Swap Rate Five Year Euro | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Adjustment to reference rate, after initial interest rate period 3.76% 3.76% 3.76%
Banco Santander, S.A., November 2023 | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Interest rate 9.625% 9.625% 9.625%
Initial interest rate term 5 years 6 months    
Reprice term 5 years    
Subordinated issue, UST rate term 5 years    
Banco Santander, S.A., November 2023 | Fixed interest rate | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Outstanding issue amount | $     $ 1,150.0
Interest rate 9.625% 9.625% 9.625%
Banco Santander, S.A., November 2023 | UST Rate Five Year US Dollar | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Adjustment to reference rate, after initial interest rate period 5.306% 5.306% 5.306%
Banco Santander, S.A., November 2023 | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Interest rate 9.625% 9.625% 9.625%
Initial interest rate term 10 years    
Reprice term 5 years    
Subordinated issue, UST rate term 5 years    
Banco Santander, S.A., November 2023 | Fixed interest rate | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Outstanding issue amount | $     $ 1,349.9
Interest rate 9.625% 9.625% 9.625%
Banco Santander, S.A., November 2023 | UST Rate Five Year US Dollar | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Adjustment to reference rate, after initial interest rate period 5.298% 5.298% 5.298%
Banco Santander, S.A., May 2024 | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Interest rate 7.00% 7.00% 7.00%
Initial interest rate term 6 years    
Reprice term 5 years    
Subordinated issue, mid-swap rate term 5 years    
Banco Santander, S.A., May 2024 | Fixed interest rate | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Outstanding issue amount | € € 1,500.0    
Interest rate 7.00% 7.00% 7.00%
Banco Santander, S.A., May 2024 | Mid Swap Rate Five Year Euro | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Adjustment to reference rate, after initial interest rate period 4.432% 4.432% 4.432%
Banco Santander, S.A., August 2024 | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Interest rate 8.00% 8.00% 8.00%
Initial interest rate term 10 years    
Reprice term 5 years    
Subordinated issue, mid-swap rate term 5 years    
Banco Santander, S.A., August 2024 | Fixed interest rate | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Outstanding issue amount | $     $ 1,499.8
Interest rate 8.00% 8.00% 8.00%
Banco Santander, S.A., August 2024 | Mid Swap Rate Five Year Euro | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Adjustment to reference rate, after initial interest rate period 3.911% 3.911% 3.911%
Banco Santander, S.A., July 2025 | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Interest rate 6.00% 6.00% 6.00%
Initial interest rate term 6 years    
Reprice term 5 years    
Subordinated issue, mid-swap rate term 5 years    
Banco Santander, S.A., July 2025 | Fixed interest rate | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Outstanding issue amount | € € 1,500.0    
Interest rate 6.00% 6.00% 6.00%
Banco Santander, S.A., July 2025 | Mid Swap Rate Five Year Euro | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Adjustment to reference rate, after initial interest rate period 3.819% 3.819% 3.819%
Banco Santander, S.A., June 2026 | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Interest rate 7.25% 7.25% 7.25%
Initial interest rate term 10 years    
Reprice term 5 years    
Subordinated issue, UST rate term 5 years    
Banco Santander, S.A., June 2026 | Fixed interest rate | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Outstanding issue amount | $     $ 1,497.4
Interest rate 7.25% 7.25% 7.25%
Banco Santander, S.A., June 2026 | Mid Swap Rate Five Year Euro | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Adjustment to reference rate, after initial interest rate period 2.837% 2.837% 2.837%
Santander Finance Preferred, S.A. (Unipersonal), September 2004 | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Outstanding issue amount | € € 143.7    
Santander Finance Preferred, S.A. (Unipersonal), September 2004 | CMS 10 interest rate | Preferred securities      
Disclosure of detailed information about financial instruments [line items]      
Interest rate 8.00% 8.00% 8.00%
Variable interest rate 0.05% 0.05% 0.05%