Right-of-use assets - Narrative (Details) - CHF (SFr) SFr in Millions	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025
Disclosure of quantitative information about right-of-use assets [abstract]
Additions	SFr 67.2	SFr 228.5

The amount of additions to right-of-use assets. [Refer: Right-of-use assets]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 16
-IssueDate 2025-01-01
-Paragraph 53
-Subparagraph h
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=16&code=ifrs-tx-2025-en-r&anchor=para_53_h&doctype=Standard
-URIDate 2025-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2027-01-01
-Name IFRS
-Number 19
-IssueDate 2025-01-01
-Paragraph 115
-Subparagraph g
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_115_g&doctype=Standard
-URIDate 2025-03-27

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2027-01-01
-Name IFRS
-Number 19
-IssueDate 2025-01-01
-Paragraph 115
-Subparagraph g
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_115_g&doctype=Standard
-URIDate 2025-03-27

Name:	ifrs-full_AdditionsToRightofuseAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration