v3.26.1
Share-Based Compensation Plans - Additional Information (Detail)
€ / shares in Units, € in Millions
 12 Months Ended
Dec. 31, 2025
EUR (€)
shares
€ / shares
Dec. 31, 2024
EUR (€)
shares
€ / shares
Dec. 31, 2023
EUR (€)
shares
€ / shares
Dec. 31, 2022
shares
Disclosure of share-based payment arrangements [line items]        
Weighted average share price | € / shares € 5.22      
Expense from share-based payment transactions | € € 6 € 10 € 13  
Expense from equity-settled share-based payment transactions | € 3 10 9  
Expense from cash-settled share-based payment transactions | € € 3 € 0 € 4  
Percentage Of Performance Shares Achievement Of The Net Debt 50.00%      
Equity Based Compensation Plan [Member]        
Disclosure of share-based payment arrangements [line items]        
Number of other equity instruments outstanding in share-based payment arrangement 6,523,939 4,438,497    
Description of vesting requirements for share-based payment arrangement For EBCP Option grants till year 2020 inclusive and prior, one-quarter of the entitlement vests on each 1 January of the four years following the Date of Option      
Outstanding options at the end of the year 11,282,865 15,165,029 19,049,997 20,348,470
Number of share options exercisable in share-based payment arrangement 11,282,865 12,183,981 11,242,584  
Number of treasury shares delivered 274,652 59,060 147,451  
Weighted average share price | € / shares € 6.07 € 5.97 € 6.11  
Weighted average share price for share options in share-based payment arrangement exercised during period at date of exercise | € / shares € 6.63      
Equity Based Compensation Plan [Member] | Restricted Shares [Member]        
Disclosure of share-based payment arrangements [line items]        
Number of other equity instruments granted in share-based payment arrangement 745,197 456,894 451,705  
Number of other equity instruments forfeited in share-based payment arrangement 255,337 196,299 67,853  
Number of other equity instruments exercised or vested in share-based payment arrangement 809,923 372,805 238,645  
Equity Based Compensation Plan [Member] | Performance Share [Member]        
Disclosure of share-based payment arrangements [line items]        
Number of other equity instruments granted in share-based payment arrangement 3,697,990 1,635,264 1,287,594  
Number of other equity instruments forfeited in share-based payment arrangement 1,036,537 355,197 86,772  
Number of other equity instruments exercised or vested in share-based payment arrangement   944,846 604,047  
Simulated Restricted Share Units [Member]        
Disclosure of share-based payment arrangements [line items]        
Number of other equity instruments granted in share-based payment arrangement 0 0 1,233,352  
Number of other equity instruments forfeited in share-based payment arrangement 195,742 282,548 172,473  
Number of other equity instruments exercised or vested in share-based payment arrangement 719,769 647,870 652,648  
Liabilities from share-based payment transactions | € € 3,904,033 € 3,525,918 € 7,290,615  
Number of other equity instruments outstanding in share-based payment arrangement 819,840 1,735,344 2,665,762