Statement Of Changes In Equity [Abstract]
| Concept | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | As at 2024-12-31 | 2024-01-01 to 2024-12-31 | As at 2024-12-31 | 2024-01-01 to 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | 2023-01-01 to 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 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Statement of changes in equity [abstract] | |||||||||||||||||||||||||||||||||||
| Statement of changes in equity [line items] | |||||||||||||||||||||||||||||||||||
| Equity | — | — | — | 
                                                643,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                21,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                39,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | 
                                                693,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                23,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                6,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                732,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                643,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | 
                                                571,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                14,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                32,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                21,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                612,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                6,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                501,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                14,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                35,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                425,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                21,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                466,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                6,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
| Changes in equity [abstract] | |||||||||||||||||||||||||||||||||||
| Comprehensive income [abstract] | |||||||||||||||||||||||||||||||||||
| Profit (loss) | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                216,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | 
                                                216,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                13,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                229,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | 
                                                285,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                275,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                10,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                275,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Comprehensive income | 
                                                9,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                225,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | 
                                                216,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                14,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                238,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | 
                                                284,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                274,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                1,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                10,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                275,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Dividends recognised as distributions to owners | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                143,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | 
                                                143,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                7,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                149,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | 
                                                143,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                129,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                14,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                129,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | 
                                                -
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |