OPERATING REVENUES - DISAGGREGATION OF NATURAL GAS UTILITY OPERATING REVENUES BY CUSTOMER CLASS (Details) - Revenues from contracts with customers - Utility segment - Transferred over time - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 482.2	$ 465.6	$ 1,451.8	$ 1,372.7
Natural gas
Disaggregation of Operating Revenues
Revenues from contracts with customers	36.6	49.3	304.2	275.9
Natural gas \| Total retail
Disaggregation of Operating Revenues
Revenues from contracts with customers	36.3	37.7	295.4	258.5
Natural gas \| Residential
Disaggregation of Operating Revenues
Revenues from contracts with customers	23.3	23.6	187.0	162.8
Natural gas \| Commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	13.0	14.1	108.4	95.7
Natural gas \| Transportation
Disaggregation of Operating Revenues
Revenues from contracts with customers	5.8	5.5	20.9	20.3
Natural gas \| Other utility
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ (5.5)	$ 6.1	$ (12.1)	$ (2.9)

OPERATING REVENUES - DISAGGREGATION OF NATURAL GAS UTILITY OPERATING REVENUES BY CUSTOMER CLASS (Details) - Revenues from contracts with customers - Utility segment - Transferred over time - USD ($)
$ in Millions

3 Months Ended

9 Months Ended

Sep. 30, 2026

Sep. 30, 2025

Sep. 30, 2026

Sep. 30, 2025

Disaggregation of Operating Revenues

Revenues from contracts with customers

$ 482.2

$ 465.6

$ 1,451.8

$ 1,372.7