v3.25.4
REVENUE FROM CONTRACTS WITH CUSTOMERS - Revenue by Major Category and Reportable Segment (Details) - CHF (SFr)
SFr in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue SFr 2,983.4 SFr 3,018.0 SFr 3,035.2
Fixed      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 1,479.9 1,530.5 1,545.3
Fixed | Subscription      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 1,240.6 1,299.1 1,335.4
Fixed | Non-Subscription And Hardware      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 239.3 231.4 209.9
Mobile      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 1,375.0 1,377.5 1,381.7
Mobile | Subscription      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 1,089.8 1,089.0 1,097.3
Mobile | Non-Subscription And Hardware      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 285.2 288.5 284.4
Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 128.5 110.0 108.2
Residential customers      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 2,107.2 2,173.1 2,247.1
Residential customers | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   0.0 0.0
Residential customers | Unadjusted Difference      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue     2,247.1
Residential customers | Fixed      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 974.0 1,047.4 1,107.4
Residential customers | Fixed | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   45.6 45.7
Residential customers | Fixed | Subscription      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 933.6 1,003.3 1,059.2
Residential customers | Fixed | Subscription | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   15.5 16.1
Residential customers | Fixed | Non-Subscription And Hardware      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 40.4 44.1 48.2
Residential customers | Fixed | Non-Subscription And Hardware | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   30.1 29.6
Residential customers | Mobile      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 1,027.9 1,033.0 1,045.2
Residential customers | Mobile | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   (8.1) (7.1)
Residential customers | Mobile | Subscription      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 821.9 824.6 843.0
Residential customers | Mobile | Subscription | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   (8.9) (9.9)
Residential customers | Mobile | Non-Subscription And Hardware      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 206.0 208.4 202.2
Residential customers | Mobile | Non-Subscription And Hardware | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   0.8 2.8
Residential customers | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 105.3 92.7 94.5
Residential customers | Other | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   (37.5) (38.6)
Business customers & Wholesale      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 859.0 830.3 776.6
Business customers & Wholesale | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   0.0 0.0
Business customers & Wholesale | Unadjusted Difference      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue     776.6
Business customers & Wholesale | Fixed      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 505.9 483.1 437.9
Business customers & Wholesale | Fixed | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   0.1 0.5
Business customers & Wholesale | Fixed | Subscription      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 307.0 295.8 276.2
Business customers & Wholesale | Fixed | Subscription | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   2.4 2.8
Business customers & Wholesale | Fixed | Non-Subscription And Hardware      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 198.9 187.3 161.7
Business customers & Wholesale | Fixed | Non-Subscription And Hardware | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   (2.3) (2.3)
Business customers & Wholesale | Mobile      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 347.1 344.5 336.5
Business customers & Wholesale | Mobile | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   0.6 0.3
Business customers & Wholesale | Mobile | Subscription      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 267.9 264.4 254.3
Business customers & Wholesale | Mobile | Subscription | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   (1.8) (0.4)
Business customers & Wholesale | Mobile | Non-Subscription And Hardware      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 79.2 80.1 82.2
Business customers & Wholesale | Mobile | Non-Subscription And Hardware | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   2.4 0.7
Business customers & Wholesale | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 6.0 2.7 2.2
Business customers & Wholesale | Other | Prior Period Reclassification Adjustments      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue   (0.7) (0.8)
Infrastructure & Support functions      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 17.2 14.6 11.5
Infrastructure & Support functions | Fixed      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 0.0 0.0 0.0
Infrastructure & Support functions | Fixed | Subscription      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 0.0 0.0 0.0
Infrastructure & Support functions | Fixed | Non-Subscription And Hardware      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 0.0 0.0 0.0
Infrastructure & Support functions | Mobile      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 0.0 0.0 0.0
Infrastructure & Support functions | Mobile | Subscription      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 0.0 0.0 0.0
Infrastructure & Support functions | Mobile | Non-Subscription And Hardware      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue 0.0 0.0 0.0
Infrastructure & Support functions | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Revenue SFr 17.2 SFr 14.6 SFr 11.5