Electric utility segment - Annual Decoupling Filings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory Projects and Legal Obligations [Line Items]
2019 Annual incremental RAM adjusted revenues,net of changes in Tax Act adjustment	$ 13.0
Annual change in accrued RBA balance as of December 31, 2018 (and associated revenue taxes) which incorporates MPIR recovery	13.4
Net annual incremental amount to be collected (refunded) under the tariffs	(1.7)
Net annual incremental amount to be collected (refunded) under the tariffs	(2.1)
Hawaiian Electric
Regulatory Projects and Legal Obligations [Line Items]
2019 Annual incremental RAM adjusted revenues,net of changes in Tax Act adjustment	6.5
Annual change in accrued RBA balance as of December 31, 2018 (and associated revenue taxes) which incorporates MPIR recovery	12.2
Net annual incremental amount to be collected (refunded) under the tariffs	(1.3)
Net annual incremental amount to be collected (refunded) under the tariffs	(7.0)
Hawaii Electric Light
Regulatory Projects and Legal Obligations [Line Items]
2019 Annual incremental RAM adjusted revenues,net of changes in Tax Act adjustment	1.1
Annual change in accrued RBA balance as of December 31, 2018 (and associated revenue taxes) which incorporates MPIR recovery	2.0
Net annual incremental amount to be collected (refunded) under the tariffs	0.0
Net annual incremental amount to be collected (refunded) under the tariffs	(0.9)
Maui Electric
Regulatory Projects and Legal Obligations [Line Items]
2019 Annual incremental RAM adjusted revenues,net of changes in Tax Act adjustment	5.4
Annual change in accrued RBA balance as of December 31, 2018 (and associated revenue taxes) which incorporates MPIR recovery	(0.8)
Net annual incremental amount to be collected (refunded) under the tariffs	(0.4)
Net annual incremental amount to be collected (refunded) under the tariffs	$ 5.8
2017 Tax Act Adjustment		$ 2.8