REGULATORY MATTERS: Level 4 (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
	Jun. 01, 2022	Mar. 31, 2022	Mar. 31, 2021	May 31, 2023	Jun. 30, 2021	Jun. 01, 2021	Jun. 01, 2020	Apr. 30, 2018	Oct. 31, 2014
Settlement Stipulation - Investment Tax Credits and Idaho Sharing Mechanism
Regulatory Matters
Additional accumulated deferred investment tax credits (ADITC) amortization		$ 0.0	$ 0.0
Idaho fixed cost adjustment mechanism
Regulatory Matters
Percentage cap on the FCA adjustment							3.00%
Idaho Jurisdiction Fixed Cost Adjustment
Regulatory Matters
Annual fixed cost adjustment mechanism deferral						$ 38.3
Subsequent Event | Idaho Power Cost Adjustment
Regulatory Matters
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 103.4
Subsequent Event | Idaho Jurisdiction Fixed Cost Adjustment
Regulatory Matters
Public Utilities, Requested Rate Increase (Decrease), Amount				(3.1)
Annual fixed cost adjustment mechanism deferral	$ 35.2
IDAHO | May 2018 Tax Reform Settlement Stipulation
Regulatory Matters
Minimum authorized return on equity								9.40%
Target authorized return on equity								10.00%
IDAHO | October 2014 Idaho Settlement Stipulation
Regulatory Matters
Investment Tax Credits, Maximum, in Rate Case									$ 45.0
IDAHO | Wildfire mitigation plan costs
Regulatory Matters
Requested deferral of costs		$ 8.8
IDAHO | Wildfire mitigation plan costs | Plant in service
Regulatory Matters
Requested deferral of costs					$ 35.0
IDAHO | Wildfire mitigation plan costs | Other Operating and Maintenance Expenses
Regulatory Matters
Requested deferral of costs					$ 47.0
IDAHO | Subsequent Event | May 2018 Tax Reform Settlement Stipulation
Regulatory Matters
Public Utilities, Requested Rate Increase (Decrease), Amount				$ (0.6)
IDAHO | Subsequent Event | Jim Bridger Plant
Regulatory Matters
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ 27.1