Statement Of Financial Position [Abstract]
| Concept | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Statement of financial position [abstract] | ||||||||||||||||||||||||
| Assets [abstract] | ||||||||||||||||||||||||
| Investments accounted for using equity method | — | — | — | — | — | — | — | 
                                                34,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                49,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Deferred tax assets | — | — | — | — | — | — | — | 
                                                1 576
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                1 509
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Cash and cash equivalents | — | — | — | — | — | — | — | 
                                                7 179
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                6 401
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                7 326
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
| Assets | — | — | — | — | — | — | — | 
                                                83 589
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                67 784
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Equity and liabilities [abstract] | ||||||||||||||||||||||||
| Equity [abstract] | ||||||||||||||||||||||||
| Issued capital | — | — | — | — | — | — | — | 
                                                500,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                500,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Retained earnings | — | — | — | — | — | — | — | 
                                                39 947
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                35 452
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other reserves | — | — | — | — | — | — | — | 
                                                2 193
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                765,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Equity attributable to owners of parent | — | — | — | — | — | — | — | 
                                                42 757
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                36 822
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-controlling interests | — | — | — | — | — | — | — | 
                                                423,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                388,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Equity | 
                                                39 947
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                500,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                423,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                2 192
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                42 757
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                1,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                117,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                43 180
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                37 210
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                35 452
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                388,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                500,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                735,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                36 822
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                30,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                105,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                33 508
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                488,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                30 228
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                500,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                2 091
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                33 020
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                107,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                94,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
| Liabilities [abstract] | ||||||||||||||||||||||||
| Deferred tax liabilities | — | — | — | — | — | — | — | 
                                                1 737
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                922,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Equity and liabilities | — | — | — | — | — | — | — | 
                                                83 589
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                67 784
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — |