Statement Of Cash Flows [Abstract]
| Concept | 2024-01-01 to 2024-12-31 | 2023-01-01 to 2023-12-31 | 2022-01-01 to 2022-12-31 | 
|---|---|---|---|
| Statement of cash flows [abstract] | |||
| Cash flows from (used in) operating activities [abstract] | |||
| Adjustments for interest expense | 
                                                270,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                255,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                226,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
| Adjustments for interest income | 
                                                81,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                46,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                25,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
| Increase (decrease) in working capital | 
                                                355,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                913,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                862,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
| Adjustments for increase (decrease) in other liabilities | 
                                                51,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                38,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                84,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
| Adjustments for impairment loss recognised in profit or loss, goodwill | — | 
                                                8,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                1,357,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
| Cash flows from (used in) investing activities [abstract] | |||
| Payments for development project expenditure | 
                                                241,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                203,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                257,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
| Cash flows from (used in) financing activities [abstract] | |||
| Dividends paid to equity holders of parent, classified as financing activities | 
                                                1,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                2,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                412,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
| Proceeds from sale or issue of treasury shares | 
                                                0
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                0
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                12,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
| Proceeds from non-current borrowings | 
                                                710,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                544,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                2,516,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
| Repayments of non-current borrowings | 
                                                763,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                754,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                1,472,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
| Cash flows from (used in) increase (decrease) in current borrowings | 
                                                30,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                29,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             | 
                                                47,000,000
                                                
                                                    
                                                        EUR
                                                    
                                                
                                             |