Retirement benefits (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Defined benefit plans
Expected payments for remainder of fiscal year	$ 2,600,000		$ 1,500,000
Retirement benefits expense	$ 15,000,000	$ 12,000,000
Number of years for which regulatory asset/liability for each utility will be amortized, beginning with respective utility's next rate case (in years)	5 years
Defined contribution plan, expenses recognized	$ 1,900,000	1,600,000
Cash contributions by the employer to defined contribution plan	3,700,000	3,700,000
Hawaiian Electric Company, Inc. and Subsidiaries
Defined benefit plans
Expected payments for remainder of fiscal year	1,200,000		600,000
Retirement benefits expense	14,000,000	11,000,000
Defined contribution plan, expenses recognized	700,000	500,000
Cash contributions by the employer to defined contribution plan	700,000	500,000
Pension benefits
Defined benefit plans
Contributions made to defined benefit plans	8,000,000	16,000,000
Contributions expected to be paid in current year	47,500,000		38,500,000
Service cost	15,382,000	17,113,000
Interest cost	21,033,000	19,234,000
Expected return on plan assets	(27,998,000)	(27,254,000)
Amortization of net prior service gain	(11,000)	(10,000)
Amortization of net actuarial (gains) losses	3,839,000	7,395,000
Net periodic pension/benefit cost (return)	12,245,000	16,478,000
Impact of PUC D&Os	12,279,000	2,657,000
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	24,524,000	19,135,000
Pension benefits | American Savings Bank (ASB)
Defined benefit plans
Contributions expected to be paid in current year	0		0
Pension benefits | Hawaiian Electric Industries, Inc.
Defined benefit plans
Contributions expected to be paid in current year	700,000		900,000
Pension benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined benefit plans
Contributions made to defined benefit plans	8,000,000	15,000,000
Contributions expected to be paid in current year	46,800,000		$ 37,600,000
Service cost	15,001,000	16,673,000
Interest cost	19,414,000	17,710,000
Expected return on plan assets	(26,164,000)	(25,607,000)
Amortization of net prior service gain	2,000	2,000
Amortization of net actuarial (gains) losses	3,576,000	6,710,000
Net periodic pension/benefit cost (return)	11,829,000	15,488,000
Impact of PUC D&Os	12,279,000	2,657,000
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	24,108,000	18,145,000
Other benefits
Defined benefit plans
Service cost	541,000	669,000
Interest cost	1,997,000	1,931,000
Expected return on plan assets	(3,086,000)	(3,192,000)
Amortization of net prior service gain	(452,000)	(452,000)
Amortization of net actuarial (gains) losses	(3,000)	(2,000)
Net periodic pension/benefit cost (return)	(1,003,000)	(1,046,000)
Impact of PUC D&Os	811,000	1,071,000
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	(192,000)	25,000
Other benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined benefit plans
Service cost	537,000	664,000
Interest cost	1,917,000	1,859,000
Expected return on plan assets	(3,035,000)	(3,140,000)
Amortization of net prior service gain	(451,000)	(451,000)
Amortization of net actuarial (gains) losses	0	0
Net periodic pension/benefit cost (return)	(1,032,000)	(1,068,000)
Impact of PUC D&Os	811,000	1,071,000
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	$ (221,000)	$ 3,000