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	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 1,042.9	$ 1,006.1	$ 2,356.7	$ 2,182.2
Natural gas
Disaggregation of Operating Revenues
Revenues from contracts with customers	79.1	84.8	377.2	325.6
Natural gas \| Total retail
Disaggregation of Operating Revenues
Revenues from contracts with customers	81.8	76.0	357.3	323.0
Natural gas \| Residential
Disaggregation of Operating Revenues
Revenues from contracts with customers	57.3	53.1	247.4	222.2
Natural gas \| Commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	24.5	22.9	109.9	100.8
Natural gas \| Transportation
Disaggregation of Operating Revenues
Revenues from contracts with customers	5.6	5.1	14.2	13.1
Natural gas \| Other utility
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ (8.3)	$ 3.7	$ 5.7	$ (10.5)

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

6 Months Ended

Jun. 30, 2026

Jun. 30, 2025

Jun. 30, 2026

Jun. 30, 2025

Disaggregation of Operating Revenues

Revenues from contracts with customers

$ 1,042.9

$ 1,006.1

$ 2,356.7

$ 2,182.2