Statement Of Cash Flows [Abstract]
| Concept | 2024-01-01 to 2024-12-31 | As at 2024-12-31 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | As at 2022-12-31 | 
|---|---|---|---|---|---|
| Statement of cash flows [abstract] | |||||
| Cash flows from (used in) operating activities [abstract] | |||||
| Cash flows from (used in) operations | 
                                                100,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
                                                34,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
| Interest received, classified as operating activities | 
                                                1,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
                                                2,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
| Cash flows from (used in) investing activities [abstract] | |||||
| Purchase of intangible assets, classified as investing activities | 
                                                62,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
                                                44,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
| Dividends received, classified as investing activities | 
                                                7,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
| Cash flows from (used in) financing activities [abstract] | |||||
| Proceeds from issuing shares | 
                                                0
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
                                                1,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
| Proceeds from borrowings, classified as financing activities | 
                                                54,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
                                                83,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
| Repayments of borrowings, classified as financing activities | 
                                                86,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
                                                1,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
| Payments of lease liabilities, classified as financing activities | 
                                                12,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
                                                11,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
| Other inflows (outflows) of cash, classified as financing activities | 
                                                3,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
                                                6,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
| Increase (decrease) in cash and cash equivalents before effect of exchange rate changes | 
                                                103,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
                                                28,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
| Effect of exchange rate changes on cash and cash equivalents [abstract] | |||||
| Effect of exchange rate changes on cash and cash equivalents | 
                                                -
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
                                                6,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | — | 
| Cash and cash equivalents | — | 
                                                30,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | — | 
                                                133,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                167,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             |