v3.26.1
Investments in Joint Ventures and Associates - Summary of Financial Information of Joint Ventures (Detail) - EUR (€)
€ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Disclosure of joint ventures [Line Items]      
Post-tax profit or loss € 980 € 676 € (199)
Other comprehensive income 412 573 421
Total comprehensive income 1,392 1,248 € 222
Santander Spain Life [member]      
Disclosure of joint ventures [Line Items]      
Post-tax profit or loss 76 74  
Other comprehensive income 3 4  
Total comprehensive income 79 78  
Santander Spain Life [member] | Aegon legal stake in the joint ventures [member]      
Disclosure of joint ventures [Line Items]      
Post-tax profit or loss 39 38  
Other comprehensive income 2 2  
Total comprehensive income 40 40  
AIFMC [member]      
Disclosure of joint ventures [Line Items]      
Post-tax profit or loss 186 202  
Other comprehensive income 0 0  
Total comprehensive income 186 202  
AIFMC [member] | Aegon legal stake in the joint ventures [member]      
Disclosure of joint ventures [Line Items]      
Post-tax profit or loss 91 99  
Other comprehensive income 0 0  
Total comprehensive income 91 99  
Other Joint ventures [member]      
Disclosure of joint ventures [Line Items]      
Post-tax profit or loss 335 192  
Other comprehensive income 5 (134)  
Total comprehensive income 340 58  
Other Joint ventures [member] | Aegon legal stake in the joint ventures [member]      
Disclosure of joint ventures [Line Items]      
Post-tax profit or loss 174 101  
Other comprehensive income 3 (67)  
Total comprehensive income € 176 € 35