Shareholders' equity - Reclassification Out Of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Revenues	$ (652,217)	$ (641,427)	$ (608,945)	$ (677,186)	$ (725,966)	$ (770,882)	$ (715,485)	$ (661,615)	$ (2,579,775)	$ (2,873,948)	$ (2,860,849)
Total reclassifications									61,911	(6,548)	29,340
Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Revenues	$ (571,095)	$ (562,568)	$ (534,215)	$ (597,442)	$ (645,333)	$ (688,330)	$ (633,784)	$ (578,495)	(2,265,320)	(2,545,942)	(2,546,525)
Total reclassifications									61,410	(6,627)	27,337
Amortization of prior service credit and net losses recognized during the period in net periodic benefit cost
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications									23,689	10,107	21,015
Amortization of prior service credit and net losses recognized during the period in net periodic benefit cost | Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications									21,550	9,550	19,012
Impact of D&Os of the PUC included in regulatory assets
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications									39,860	(16,177)	8,325
Impact of D&Os of the PUC included in regulatory assets | Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications									39,860	(16,177)	8,325
Amount reclassified from AOCI | Net unrealized gains (losses) on securities
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Revenues									$ (1,638)	$ (478)	$ 0