Financial assets and liabilities at fair value - Financial assets and liabilities at fair value in level 3 (Details) - SEK (kr) kr in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024
Reconciliation of changes in fair value measurement, liabilities [abstract]
Financial liabilities at beginning of period	kr (330,209)
Financial liabilities at end of period	(314,304)	kr (330,209)
Reconciliation of changes in fair value measurement assets liabilities net [abstract]
Gains (losses) recognised in profit or loss attributable to change in unrealised gains or losses for assets and liabilities held at end of period, fair value measurement	(10)	1
Level 3
Reconciliation of changes in fair value measurement assets liabilities net [abstract]
Financial assets and liabilities at fair value in level 3, at the beginning of period	(4,903)	(10,550)
Settlements & sales	588	6,046
Gains (+) and losses (–) through profit or loss	(10)	11
Gains (+) and losses (-) through other comprehen-sive income	(22)	3
Currency exchange-rate effects	686	(413)
Financial assets and liabilities at fair value in level 3, at the end of period	(3,661)	(4,903)
Debt securities issued
Reconciliation of changes in fair value measurement, liabilities [abstract]
Financial liabilities at beginning of period	(316,375)
Financial liabilities at end of period	(300,906)	(316,375)
Debt securities issued \| Level 3
Reconciliation of changes in fair value measurement, liabilities [abstract]
Financial liabilities at beginning of period	(3,452)	(8,271)
Settlements & sales	414	4,870
Gains (+) and losses (–) through profit or loss	(32)	(81)
Gains (+) and losses (-) through other comprehen-sive income	(22)	3
Currency exchange-rate effects	494	27
Financial liabilities at end of period	(2,598)	(3,452)
Derivatives
Reconciliation of changes in fair value measurement, liabilities [abstract]
Financial liabilities at beginning of period	(5,227)
Financial liabilities at end of period	(8,988)	(5,227)
Derivatives \| Level 3
Reconciliation of changes in fair value measurement assets liabilities net [abstract]
Financial assets and liabilities at fair value in level 3, at the beginning of period	(1,451)	(2,279)
Settlements & sales	174	1,176
Gains (+) and losses (–) through profit or loss	22	92
Currency exchange-rate effects	192	(440)
Financial assets and liabilities at fair value in level 3, at the end of period	kr (1,063)	kr (1,451)

The fair value of financial liabilities. [Refer: At fair value [member]; Financial liabilities]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2025-01-01
-Paragraph 25
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2025-en-r&anchor=para_25&doctype=Standard
-URIDate 2025-03-27

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- Definition

The gains (losses) excluding exchange differences, recognised in other comprehensive income, on the fair value measurement of liabilities. [Refer: At fair value [member]; Other comprehensive income]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IFRS
-Number 13
-IssueDate 2025-01-01
-Paragraph 93
-Subparagraph e
-Clause ii
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2025-en-r&anchor=para_93_e_ii&doctype=Standard
-URIDate 2025-03-27

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The gains (losses) excluding exchange differences, recognised in profit or loss, on the fair value measurement of liabilities. [Refer: At fair value [member]]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IFRS
-Number 13
-IssueDate 2025-01-01
-Paragraph 93
-Subparagraph e
-Clause i
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2025-en-r&anchor=para_93_e_i&doctype=Standard
-URIDate 2025-03-27

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- Definition

The amount of assets less the amount of liabilities.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IFRS
-Number 1
-IssueDate 2025-01-01
-Paragraph IG63
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=1&code=ifrs-tx-2025-en-r&anchor=para_IG63&doctype=Implementation%20Guidance
-URIDate 2025-03-27

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Note Expiry date 2027-01-01
-Name IAS
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-IssueDate 2025-01-01
-Paragraph 112
-Subparagraph c
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2025-en-b&anchor=para_112_c&doctype=Standard
-URIDate 2025-03-27

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The decrease (increase) in net assets (liabilities) due to losses (gains) recognised in other comprehensive income on the fair value measurement of net assets and liabilities.

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No definition available.

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The amount of gains (losses) recognised in profit or loss attributable to change in unrealised gains or losses for assets and liabilities held at end of period.

+ References

No definition available.

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The gains (losses) recognised in profit or loss on the fair value measurement of currency exchange-rate effects on net assets and liabilities.

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The gains (losses) recognised in profit or loss on the fair value measurement of currency exchange-rate effects on liabilities.

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The gains (losses) recognised in profit or loss on the fair value measurement of net assets and liabilities.

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The decrease in the fair value measurement of liabilities resulting from settlements & sales.

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The decrease in the fair value measurement of net assets and liabilities resulting from settlements & sales.

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