v3.25.4
Post-employment benefits - Text Details (Detail) - EUR (€)
€ in Millions
 12 Months Ended
Dec. 31, 2026
Dec. 31, 2025
Dec. 31, 2024
Post-employment benefits [Line Items]      
Percentage of unquoted assets   38.00% 22.00%
Percentage of reasonably possible decrease in actuarial assumption   1.00%  
Percentage of reasonably possible increase in actuarial assumption   1.00%  
Weighted average duration of defined benefit obligation   9 years 10 years
Forecast      
Post-employment benefits [Line Items]      
Employer contributions € 382    
Estimate of benefit payments expected to be paid from defined benefit plan 42    
Current service cost, defined benefit plans 30    
Interest expense (income), defined benefit plans 21    
Forecast | Pension defined benefit plans      
Post-employment benefits [Line Items]      
Employer contributions 24    
Forecast | Pension defined contribution plan      
Post-employment benefits [Line Items]      
Employer contributions 316    
Germany      
Post-employment benefits [Line Items]      
Actuarial assumption of mortality rates   0.93  
Weighted average duration of defined benefit obligation   10 years  
Germany | Bottom of range      
Post-employment benefits [Line Items]      
Age   60  
Germany | Top of range      
Post-employment benefits [Line Items]      
Age   85  
Germany | Forecast      
Post-employment benefits [Line Items]      
Estimate of benefit payments expected to be paid from defined benefit plan 20    
Germany | Forecast | Pension defined benefit plans      
Post-employment benefits [Line Items]      
Employer contributions 10    
United States      
Post-employment benefits [Line Items]      
Weighted average duration of defined benefit obligation   7 years  
United States | Forecast      
Post-employment benefits [Line Items]      
Estimate of benefit payments expected to be paid from defined benefit plan 9    
United States | Forecast | Pension defined benefit plans      
Post-employment benefits [Line Items]      
Employer contributions 0    
United States | Forecast | Pension defined contribution plan      
Post-employment benefits [Line Items]      
Employer contributions 111    
Other countries      
Post-employment benefits [Line Items]      
Weighted average duration of defined benefit obligation   9 years  
Other countries | Forecast      
Post-employment benefits [Line Items]      
Estimate of benefit payments expected to be paid from defined benefit plan 13    
Other countries | Forecast | Pension defined benefit plans      
Post-employment benefits [Line Items]      
Employer contributions 14    
Other countries | Forecast | Pension defined contribution plan      
Post-employment benefits [Line Items]      
Employer contributions 63    
Netherlands | Forecast | Pension defined contribution plan      
Post-employment benefits [Line Items]      
Employer contributions € 142