v3.26.1
Provisions for employee benefits - Maturity analysis (Details) - EUR (€)
€ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Disclosure Of Benefit Plans [Line Items]    
Net benefit liability (asset) € 596 € 681
Other benefit plans    
Disclosure Of Benefit Plans [Line Items]    
Net benefit liability (asset) € 252 € 310
Other benefit plans | Average    
Disclosure Of Benefit Plans [Line Items]    
Weighted average duration of benefit obligation 2 years 1 month 6 days 2 years 1 month 6 days
Other benefit plans | within 1 year    
Disclosure Of Benefit Plans [Line Items]    
Net benefit liability (asset) € 90 € 108
Other benefit plans | Later than one year and not later than two years    
Disclosure Of Benefit Plans [Line Items]    
Net benefit liability (asset) 79 92
Other benefit plans | Later than two years and not later than three years    
Disclosure Of Benefit Plans [Line Items]    
Net benefit liability (asset) 64 80
Other benefit plans | Later than three years and not later than four years    
Disclosure Of Benefit Plans [Line Items]    
Net benefit liability (asset) 5 13
Other benefit plans | Later than four years and not later than five years    
Disclosure Of Benefit Plans [Line Items]    
Net benefit liability (asset) 3 5
Other benefit plans | beyond 5 years    
Disclosure Of Benefit Plans [Line Items]    
Net benefit liability (asset) 11 12
Italian defined benefit plans    
Disclosure Of Benefit Plans [Line Items]    
Net benefit liability (asset) € 143 € 151
Italian defined benefit plans | Average    
Disclosure Of Benefit Plans [Line Items]    
Weighted average duration of defined benefit obligation 5 years 9 months 18 days 6 years 1 month 6 days
Italian defined benefit plans | within 1 year    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) € 18 € 19
Italian defined benefit plans | Later than one year and not later than two years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) 16 16
Italian defined benefit plans | Later than two years and not later than three years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) 17 16
Italian defined benefit plans | Later than three years and not later than four years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) 18 17
Italian defined benefit plans | Later than four years and not later than five years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) 18 18
Italian defined benefit plans | beyond 5 years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) 56 65
Foreign defined benefit plan    
Disclosure Of Benefit Plans [Line Items]    
Net benefit liability (asset) € 89 € 108
Foreign defined benefit plan | Average    
Disclosure Of Benefit Plans [Line Items]    
Weighted average duration of defined benefit obligation 12 years 4 months 24 days 13 years 1 month 6 days
Foreign defined benefit plan | within 1 year    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) € 17 € 24
Foreign defined benefit plan | Later than one year and not later than two years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) 25 26
Foreign defined benefit plan | Later than two years and not later than three years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) 19 21
Foreign defined benefit plan | Later than three years and not later than four years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) 21 16
Foreign defined benefit plan | Later than four years and not later than five years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) 20 19
Foreign defined benefit plan | beyond 5 years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) 245 263
FISDE and other foreign medical plans    
Disclosure Of Benefit Plans [Line Items]    
Net benefit liability (asset) € 112 € 112
FISDE and other foreign medical plans | Average    
Disclosure Of Benefit Plans [Line Items]    
Weighted average duration of defined benefit obligation 10 years 10 months 24 days 11 years 3 months 18 days
FISDE and other foreign medical plans | within 1 year    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) € 8 € 8
FISDE and other foreign medical plans | Later than one year and not later than two years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) 8 7
FISDE and other foreign medical plans | Later than two years and not later than three years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) 8 7
FISDE and other foreign medical plans | Later than three years and not later than four years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) 7 7
FISDE and other foreign medical plans | Later than four years and not later than five years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) 7 7
FISDE and other foreign medical plans | beyond 5 years    
Disclosure Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) € 74 € 76