Regulatory matters - WUTC (Details) - Natural gas distribution - WUTC - Cascade Natural Gas $ in Millions	Dec. 11, 2024 USD ($)	Mar. 29, 2024 USD ($)	Apr. 30, 2025 USD ($)
Public Utilities, General Disclosures [Line Items]
Public utilities, annual revenue increase (decrease)			$ (3.7)
Public utilities, annual revenue increase (decrease), percentage			(0.005)
Pending Rate Case, Multi-Year, Year One
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	$ 29.8	$ 43.8
Public utilities, requested rate increase (decrease), percentage	7.90%	11.60%
Pending Rate Case, Multi-Year, Year Two
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	$ 10.8	$ 11.7
Public utilities, requested rate increase (decrease), percentage	2.60%	2.80%