REGULATORY MATTERS: Oregon Base Rate Changes (Details) - USD ($) $ in Millions						12 Months Ended
	Jun. 01, 2020	Jan. 01, 2020	Jul. 01, 2017	Oct. 01, 2012	Mar. 01, 2012	May 31, 2019
Oregon Base Rate Changes
Oregon Base Rate Changes [Line Items]
Approved Rate Increase (Decrease), Amount					$ 1.8
Approved Return on Equity, Percentage					9.90%
Authorized Rate of Return in Rate Case					7.757%
OREGON | Base rate adjustment request for potential Valmy closure [Member] [Member]
Oregon Base Rate Changes [Line Items]
Approved Rate Increase (Decrease), Amount			$ 1.1
OREGON | Oregon Base Rate Changes
Oregon Base Rate Changes [Line Items]
Approved Rate Increase (Decrease), Amount				$ 3.0
Annual recurring | OREGON | Valmy Plant
Oregon Base Rate Changes [Line Items]
Approved Rate Increase (Decrease), Amount		$ 3.2				$ 2.5
Annual recurring | OREGON | May 2018 Tax Reform Settlement Stipulation
Oregon Base Rate Changes [Line Items]
Approved Rate Increase (Decrease), Amount						$ (1.5)
Subsequent Event [Member] | Annual recurring | OREGON | May 2018 Tax Reform Settlement Stipulation
Oregon Base Rate Changes [Line Items]
Approved Rate Increase (Decrease), Amount	$ (1.5)