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Employee benefits - Additional Information (Detail)
12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Italian leaving indemnities (TFR)    
Employee Benefits [Line Items]    
Weighted average duration of defined benefit obligation 7 years 2 months 12 days 7 years 10 months 24 days
Leaving indemnities | China    
Employee Benefits [Line Items]    
Weighted average duration of defined benefit obligation 8 years 6 months 9 years 8 months 12 days
Leaving indemnities | Spain    
Employee Benefits [Line Items]    
Weighted average duration of defined benefit obligation 7 years 4 months 24 days 10 years 2 months 12 days