BENEFIT PLANS: Schedule Defined Benefit Plans Disclosures (Details) - USD ($)		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in Fair Value of Plan Assets [Roll Forward]
Employer contributions		$ 7,900,000	$ 7,700,000	$ 7,700,000
Noncurrent liabilities		(634,070,000)	(519,570,000)
Less amount recorded as regulatory assets		1,558,895,000	1,383,059,000
Pension Plan
Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1		1,134,752,000	951,857,000
Service cost		42,987,000	34,061,000	37,836,000
Interest cost		40,013,000	42,312,000	38,833,000
Actuarial (gain) loss		163,610,000	147,784,000
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		0	0
Benefits Paid		43,967,000	41,262,000
Projected benefit obligation at December 31		1,337,395,000	1,134,752,000	951,857,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value at January 1		763,119,000	650,604,000
Actual return (loss) on plan assets		112,451,000	113,777,000
Employer contributions		40,000,000	40,000,000
Benefits Paid		(43,967,000)	(41,262,000)
Fair value at December 31		871,603,000	763,119,000	650,604,000
Funded status at end of year		(465,792,000)	(371,633,000)
Other current liabilities		0	0
Noncurrent liabilities		(465,792,000)	(371,633,000)
Net amount recognized		(465,792,000)	(371,633,000)
Net loss		437,859,000	347,785,000
Prior service cost		49,000	56,000
Subtotal		437,908,000	347,841,000
Less amount recorded as regulatory assets	[1]	437,908,000	347,841,000
Net amount recognized in accumulated other comprehensive income		0	0
Accumulated benefit obligation		1,115,923,000	958,586,000
Senior Management Security Plan
Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1		122,443,000	102,318,000
Service cost		213,000	(181,000)	(316,000)
Interest cost		4,350,000	4,575,000	4,248,000
Actuarial (gain) loss		13,420,000	17,888,000
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		130,000	2,839,000
Benefits Paid		5,765,000	4,996,000
Projected benefit obligation at December 31		134,791,000	122,443,000	102,318,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value at January 1		0	0
Actual return (loss) on plan assets		0	0
Employer contributions		0	0
Benefits Paid		0	0
Fair value at December 31		0	0	$ 0
Funded status at end of year		(134,791,000)	(122,443,000)
Other current liabilities		(6,154,000)	(5,911,000)
Noncurrent liabilities		(128,637,000)	(116,532,000)
Net amount recognized		(134,791,000)	(122,443,000)
Net loss		55,537,000	45,851,000
Prior service cost		2,983,000	3,143,000
Subtotal		58,520,000	48,994,000
Less amount recorded as regulatory assets		0	0
Net amount recognized in accumulated other comprehensive income		58,520,000	48,994,000
Accumulated benefit obligation		$ 119,517,000	$ 109,966,000

[1] Changes in the funded status of the pension plan that would be recorded in accumulated other comprehensive income for an unregulated entity are recorded as a regulatory asset for Idaho Power as Idaho Power believes it is probable that an amount equal to the regulatory asset will be collected through the setting of future rates.