EMPLOYEE BENEFIT OBLIGAITONS - Asset Allocation of Plan Assets (Details) - CHF (SFr) SFr in Millions	Dec. 31, 2025	Dec. 31, 2024
Classes of plan assets, fair value monetary amounts [abstract]
Cash and cash equivalents	SFr 5.3	SFr 12.1
Equity securities	323.1	301.6
Debt securities	305.2	305.8
Real estate	165.2	168.5
Other	77.2	63.4
Total	SFr 876.0	SFr 851.4
Quoted
Classes of plan assets, fair value percentage amounts [abstract]
Cash and cash equivalents	0.00%	0.00%
Equity securities	36.90%	35.40%
Debt securities	34.80%	35.90%
Real estate	0.00%	1.50%
Other	0.00%	0.00%
Total	71.70%	72.80%
Unquoted
Classes of plan assets, fair value percentage amounts [abstract]
Cash and cash equivalents	0.60%	1.40%
Equity securities	0.00%	0.00%
Debt securities	0.00%	0.00%
Real estate	18.90%	18.30%
Other	8.80%	7.40%
Total	28.30%	27.20%

The amount cash and cash equivalents contribute to the fair value of defined benefit plan assets. [Refer: Cash and cash equivalents; Plan assets, at fair value; Defined benefit plans [domain]]

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The percentage cash and cash equivalents contribute to the fair value of defined benefit plan assets. [Refer: Cash and cash equivalents; Plan assets, at fair value; Defined benefit plans [domain]] [Contrast: Cash and cash equivalents, amount contributed to fair value of plan assets]

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The amount instruments representing debt (rather than equity) contribute to the fair value of defined benefit plan assets. [Refer: Plan assets, at fair value; Defined benefit plans [domain]]

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The amount other types of assets not separately disclosed contribute to the fair value of defined benefit plan assets. [Refer: Plan assets, at fair value; Defined benefit plans [domain]]

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The percentage other types of assets not separately disclosed contribute to the fair value of defined benefit plan assets. [Refer: Plan assets, at fair value; Defined benefit plans [domain]] [Contrast: Other assets, amount contributed to fair value of plan assets]

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The fair value of defined benefit plan assets. Plan assets comprise assets held by a long-term employee benefit fund and qualifying insurance policies. [Refer: At fair value [member]]

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Plan Assets, Percentage, At Fair Value

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