v3.26.1
Provisions for employee benefits - Present value of employee benefits, estimated by applying actuarial techniques (Details) - EUR (€)
€ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net benefit liability (asset) at beginning of year € 681  
Net benefit liability (asset) at end of year 596 € 681
Other benefit plans    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net benefit liability (asset) at beginning of year 310  
Net benefit liability (asset) at end of year 252 310
Defined benefit plan    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net benefit liability (asset) at beginning of year 371  
Net benefit liability (asset) at end of year 344 371
Italian defined benefit plans    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net benefit liability (asset) at beginning of year 151  
Net benefit liability (asset) at end of year 143 151
Foreign defined benefit plan    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net benefit liability (asset) at beginning of year 108  
Net benefit liability (asset) at end of year 89 108
FISDE and other foreign medical plans    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net benefit liability (asset) at beginning of year 112  
Net benefit liability (asset) at end of year 112 112
Present value of benefit liabilities    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) at beginning of year 942 1,007
Current service cost 66 71
Interest cost/income 33 38
Remeasurements: (7) (24)
- actuarial (gains) losses due to changes in demographic assumptions (7) (1)
- actuarial (gains) losses due to changes in financial assumptions (5) (17)
- experience (gains) losses 5 (6)
Past service cost and (gains) losses settlements (3) 12
Plan contributions: 1 2
- employee contributions 1 2
Benefits paid (155) (216)
Reclassification to liabilities directly associated with assets held for sale (17)  
Currency translation differences and other changes (6) 52
Net defined benefit liability (asset) at end of year 854 942
Present value of benefit liabilities | Other benefit plans    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) at beginning of year 310 353
Current service cost 57 56
Interest cost/income 8 11
Remeasurements: (8) 1
- actuarial (gains) losses due to changes in financial assumptions (3) 5
- experience (gains) losses (5) (4)
Past service cost and (gains) losses settlements (9) 3
Benefits paid (105) (113)
Reclassification to liabilities directly associated with assets held for sale (1)  
Currency translation differences and other changes   (1)
Net defined benefit liability (asset) at end of year 252 310
Present value of benefit liabilities | Defined benefit plan    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) at beginning of year 632 654
Current service cost 9 15
Interest cost/income 25 27
Remeasurements: 1 (25)
- 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)
Past service cost and (gains) losses settlements 6 9
Plan contributions: 1 2
- employee contributions 1 2
Benefits paid (50) (103)
Reclassification to liabilities directly associated with assets held for sale (16)  
Currency translation differences and other changes (6) 53
Net defined benefit liability (asset) at end of year 602 632
Present value of benefit liabilities | Italian defined benefit plans    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) at beginning of year 151 156
Current service cost 1 1
Interest cost/income 5 5
Remeasurements: (4) (1)
- actuarial (gains) losses due to changes in financial assumptions (1)  
- experience (gains) losses (3) (1)
Benefits paid (11) (10)
Currency translation differences and other changes 1  
Net defined benefit liability (asset) at end of year 143 151
Present value of benefit liabilities | Foreign defined benefit plan    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) at beginning of year 369 380
Current service cost 6 12
Interest cost/income 17 18
Remeasurements: 7 (22)
- 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
Past service cost and (gains) losses settlements 1 9
Plan contributions: 1 2
- employee contributions 1 2
Benefits paid (31) (85)
Reclassification to liabilities directly associated with assets held for sale (16)  
Currency translation differences and other changes (7) 55
Net defined benefit liability (asset) at end of year 347 369
Present value of benefit liabilities | FISDE and other foreign medical plans    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net defined benefit liability (asset) at beginning of year 112 118
Current service cost 2 2
Interest cost/income 3 4
Remeasurements: (2) (2)
- actuarial (gains) losses due to changes in financial assumptions (1)  
- experience (gains) losses (1) (2)
Past service cost and (gains) losses settlements 5  
Benefits paid (8) (8)
Currency translation differences and other changes   (2)
Net defined benefit liability (asset) at end of year 112 112
Plan assets    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net benefit liability (asset) at beginning of year 263 261
Interest cost/income 18 14
Return on plan assets (8) (17)
Administrative fees paid (1) (1)
Plan contributions: 21 25
- employee contributions 1 2
- employer contributions 20 23
Benefits paid (24) (25)
Reclassification to liabilities directly associated with assets held for sale (1)  
Currency translation differences and other changes (8) 6
Net benefit liability (asset) at end of year 260 263
Plan assets | Defined benefit plan    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net benefit liability (asset) at beginning of year 263 261
Interest cost/income 18 14
Return on plan assets (8) (17)
Administrative fees paid (1) (1)
Plan contributions: 21 25
- employee contributions 1 2
- employer contributions 20 23
Benefits paid (24) (25)
Reclassification to liabilities directly associated with assets held for sale (1)  
Currency translation differences and other changes (8) 6
Net benefit liability (asset) at end of year 260 263
Plan assets | Foreign defined benefit plan    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net benefit liability (asset) at beginning of year 263 261
Interest cost/income 18 14
Return on plan assets (8) (17)
Administrative fees paid (1) (1)
Plan contributions: 21 25
- employee contributions 1 2
- employer contributions 20 23
Benefits paid (24) (25)
Reclassification to liabilities directly associated with assets held for sale (1)  
Currency translation differences and other changes (8) 6
Net benefit liability (asset) at end of year 260 263
Asset ceiling    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net benefit liability (asset) at beginning of year 2 2
Net benefit liability (asset) at end of year 2 2
Asset ceiling | Defined benefit plan    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net benefit liability (asset) at beginning of year 2 2
Net benefit liability (asset) at end of year 2 2
Asset ceiling | Foreign defined benefit plan    
Disclosure Of Liability Asset Of Benefit Plans [Line Items]    
Net benefit liability (asset) at beginning of year 2 2
Net benefit liability (asset) at end of year € 2 € 2