v3.26.1
Investments in Joint Ventures and Associates - Summary of Overview of Summarized Financial Information to Carrying Amount 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]      
Fair value adjustments € (26,228) € (20,665) € (20,540)
Carrying amount 1,566 1,503 € 1,430
ASR [member]      
Disclosure of joint ventures [Line Items]      
Net assets of joint venture as presented above 8,774 8,863  
Net assets of joint venture excluding goodwill 8,723 8,827  
Fair value adjustments 66 50  
Goodwill on acquisition 94 117  
Carrying amount 2,264 2,811  
Aegon [member] | ASR [member]      
Disclosure of joint ventures [Line Items]      
Net assets of joint venture excluding goodwill 2,104 2,644  
Santander Spain Life [member]      
Disclosure of joint ventures [Line Items]      
Net assets of joint venture as presented above 624 657  
Net assets of joint venture excluding goodwill 545 577  
Goodwill on acquisition 80 80  
Carrying amount 357 374  
Santander Spain Life [member] | Aegon [member]      
Disclosure of joint ventures [Line Items]      
Net assets of joint venture excluding goodwill 278 294  
AIFMC [member]      
Disclosure of joint ventures [Line Items]      
Net assets of joint venture as presented above 1,024 985  
Net assets of joint venture excluding goodwill 1,024 985  
Goodwill on acquisition 1 1  
Carrying amount 502 483  
AIFMC [member] | Aegon [member]      
Disclosure of joint ventures [Line Items]      
Net assets of joint venture excluding goodwill 502 483  
Other Joint ventures [member]      
Disclosure of joint ventures [Line Items]      
Net assets of joint venture as presented above 1,279 1,159  
Net assets of joint venture excluding goodwill 1,160 1,040  
Goodwill on acquisition 119 120  
Carrying amount 707 646  
Other Joint ventures [member] | Aegon [member]      
Disclosure of joint ventures [Line Items]      
Net assets of joint venture excluding goodwill € 588 € 526