Retirement benefits (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Defined benefit plans
Expected payments for remainder of fiscal year	$ 3,000,000		$ 1,000,000
Retirement benefits expense	$ 12,000,000	$ 9,000,000
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	$ 1,600,000	1,500,000
Cash contributions by the employer to defined contribution plan	3,700,000	2,900,000
Hawaiian Electric Company, Inc. and Subsidiaries
Defined benefit plans
Expected payments for remainder of fiscal year	1,000,000		500,000
Retirement benefits expense	11,000,000	8,000,000
Defined contribution plan, expenses recognized	500,000	500,000
Cash contributions by the employer to defined contribution plan	500,000	500,000
Pension benefits
Defined benefit plans
Contributions made to defined benefit plans	16,000,000	17,000,000
Contributions expected to be paid in current year	62,000,000		67,000,000
Service cost	17,113,000	16,494,000
Interest cost	19,234,000	20,216,000
Expected return on plan assets	(27,254,000)	(25,721,000)
Amortization of net prior service gain	(10,000)	(14,000)
Amortization of net actuarial loss (gain)	7,395,000	6,513,000
Net periodic pension/benefit cost (return)	16,478,000	17,488,000
Impact of PUC D&Os	2,657,000	(5,156,000)
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	19,135,000	12,332,000
Pension benefits | American Savings Bank (ASB)
Defined benefit plans
Contributions expected to be paid in current year	0		0
Pension benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined benefit plans
Contributions made to defined benefit plans	15,000,000	17,000,000
Contributions expected to be paid in current year	61,000,000		66,000,000
Service cost	16,673,000	16,094,000
Interest cost	17,710,000	18,589,000
Expected return on plan assets	(25,607,000)	(24,011,000)
Amortization of net prior service gain	2,000	2,000
Amortization of net actuarial loss (gain)	6,710,000	6,006,000
Net periodic pension/benefit cost (return)	15,488,000	16,680,000
Impact of PUC D&Os	2,657,000	(5,156,000)
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	18,145,000	11,524,000
Pension benefits | Hawaiian Electric Industries, Inc.
Defined benefit plans
Contributions expected to be paid in current year	1,000,000		$ 1,000,000
Other benefits
Defined benefit plans
Service cost	669,000	840,000
Interest cost	1,931,000	2,411,000
Expected return on plan assets	(3,192,000)	(3,066,000)
Amortization of net prior service gain	(452,000)	(449,000)
Amortization of net actuarial loss (gain)	(2,000)	366,000
Net periodic pension/benefit cost (return)	(1,046,000)	102,000
Impact of PUC D&Os	1,071,000	146,000
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	25,000	248,000
Other benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined benefit plans
Service cost	664,000	835,000
Interest cost	1,859,000	2,327,000
Expected return on plan assets	(3,140,000)	(3,017,000)
Amortization of net prior service gain	(451,000)	(451,000)
Amortization of net actuarial loss (gain)	0	359,000
Net periodic pension/benefit cost (return)	(1,068,000)	53,000
Impact of PUC D&Os	1,071,000	146,000
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	$ 3,000	$ 199,000