BORROWINGS - Reconciliation of Third-Party Debt (Details) - CHF (SFr) SFr in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Disclosure of detailed information about borrowings [line items] | ||
| Borrowings | SFr 4,337.2 | SFr 4,676.8 |
| Accrued interest on third-party debt | 98.5 | 57.4 |
| Total debt including interest | 4,435.7 | 4,734.2 |
| Current portion of debt | 485.7 | 407.4 |
| Non-current portion of debt | 3,950.0 | 4,326.8 |
| Principal amount | ||
| Disclosure of detailed information about borrowings [line items] | ||
| Borrowings | 4,345.7 | 4,687.1 |
| Deferred Financing Costs, Discounts And Premiums, Net | ||
| Disclosure of detailed information about borrowings [line items] | ||
| Borrowings | SFr (8.5) | SFr (10.3) |