v3.26.1
Provisions for employee benefits - Costs of defined benefit plans recognized in other comprehensive income (Details) - EUR (€)
€ in Millions
12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Disclosure Of Benefit Plans [Line Items]      
Actuarial (gains)/losses due to changes in demographic assumptions € (7) € (1)  
Actuarial (gains)/losses due to changes in financial assumptions (2) (22)  
Experience (gains) losses 10 (2)  
Return on plan assets 8 17  
Remeasurements 9 (8) € 31
Italian defined benefit plans      
Disclosure Of Benefit Plans [Line Items]      
Actuarial (gains)/losses due to changes in financial assumptions (1)    
Experience (gains) losses (3) (1)  
Remeasurements (4) (1)  
Foreign defined benefit plan      
Disclosure Of Benefit Plans [Line Items]      
Actuarial (gains)/losses due to changes in demographic assumptions (7) (1)  
Actuarial (gains)/losses due to changes in financial assumptions   (22)  
Experience (gains) losses 14 1  
Return on plan assets 8 17  
Remeasurements 15 (5)  
FISDE and other foreign medical plans      
Disclosure Of Benefit Plans [Line Items]      
Actuarial (gains)/losses due to changes in financial assumptions (1)    
Experience (gains) losses (1) (2)  
Remeasurements € (2) € (2)