Income taxes - Schedule of Major Components of Income Tax (Details) - CHF (SFr) SFr in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income Taxes [Abstract]
Current income taxes	SFr 76.0	SFr 74.0	SFr 35.7
Deferred income taxes	(74.5)	(36.6)	(46.2)
Income tax expense (benefit)	SFr 1.5	SFr 37.4	SFr (10.5)

- References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 8
-IssueDate 2025-01-01
-Paragraph 23
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-URIDate 2025-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2027-01-01
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2027-01-01
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+ Details