Statement Of Changes In Equity [Abstract]
| Concept | 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 | 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 | 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 | 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 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | As at 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 | 2023-01-01 to 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 changes in equity [abstract] | ||||||||||||||||||||||||||||||||||||||||
| Statement of changes in equity [line items] | ||||||||||||||||||||||||||||||||||||||||
| 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
                                                    
                                                
                                             | 
| Changes in equity [abstract] | ||||||||||||||||||||||||||||||||||||||||
| Comprehensive income [abstract] | ||||||||||||||||||||||||||||||||||||||||
| Profit (loss) | 
                                                8 731
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | 
                                                8 731
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                25,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                8 756
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | 
                                                9 458
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                9 431
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                27,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                9 431
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Other comprehensive income | 
                                                1 586
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                1 456
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | 
                                                159,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                3,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                1 589
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                29,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | 
                                                1 742
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                1 726
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                16,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                306,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                1 356
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                64,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Comprehensive income | 
                                                10 317
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                1 456
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | 
                                                8 890
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                28,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                10 345
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                29,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | 
                                                7 716
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                7 706
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                10,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                9 126
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                1 356
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                64,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Dividends recognised as distributions to owners | 
                                                4 591
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | 
                                                4 591
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                2,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                4 593
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | 
                                                4 106
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                4 103
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                3,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                4 103
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Increase (decrease) through share-based payment transactions, equity | 
                                                13,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | 
                                                13,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                13,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | 
                                                25,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                25,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                25,000,000
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        SEK
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |