Fair value measurements - Carrying or Notional Amount, Fair Value and Placement in the Fair Value Hierarchy of the Company’s Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Aug. 01, 2025	Dec. 31, 2024
Significant  other observable  inputs (Level 2)
Financial assets
Derivative assets		$ 1,000
Carrying or notional amount
Financial assets
Derivative assets			$ 29,312
Financial liabilities
Short-term borrowings, net			48,623
Long-term debt, net	$ 2,438,691		2,799,558
Carrying or notional amount | Money Market Funds
Financial assets
Money market mutual funds	925,258		1,162,259
Carrying or notional amount | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Short-term borrowings, net			48,623
Long-term debt, net	2,182,533		1,901,214
Carrying or notional amount | Hawaiian Electric Company, Inc. and Subsidiaries | Money Market Funds
Financial assets
Money market mutual funds	402,575		115,599
Estimated fair value
Financial assets
Derivative assets			$ 1,629
Derivative asset, statement of financial position			Other
Financial liabilities
Short-term borrowings, net			$ 48,623
Long-term debt, net	2,104,038		2,196,403
Estimated fair value | Money Market Funds
Financial assets
Money market mutual funds	925,258		1,162,259
Estimated fair value | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Short-term borrowings, net			48,623
Long-term debt, net	1,871,292		1,446,316
Estimated fair value | Hawaiian Electric Company, Inc. and Subsidiaries | Money Market Funds
Financial assets
Money market mutual funds	402,575		115,599
Estimated fair value | Quoted prices in active markets for identical assets (Level 1)
Financial assets
Derivative assets			0
Financial liabilities
Short-term borrowings, net			0
Long-term debt, net	0		0
Estimated fair value | Quoted prices in active markets for identical assets (Level 1) | Money Market Funds
Financial assets
Money market mutual funds	925,258		1,162,259
Estimated fair value | Quoted prices in active markets for identical assets (Level 1) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Short-term borrowings, net			0
Long-term debt, net	0		0
Estimated fair value | Quoted prices in active markets for identical assets (Level 1) | Hawaiian Electric Company, Inc. and Subsidiaries | Money Market Funds
Financial assets
Money market mutual funds	402,575		115,599
Estimated fair value | Significant  other observable  inputs (Level 2)
Financial assets
Derivative assets			1,629
Financial liabilities
Short-term borrowings, net			48,623
Long-term debt, net	2,104,038		2,196,403
Estimated fair value | Significant  other observable  inputs (Level 2) | Money Market Funds
Financial assets
Money market mutual funds	0		0
Estimated fair value | Significant  other observable  inputs (Level 2) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Short-term borrowings, net			48,623
Long-term debt, net	1,871,292		1,446,316
Estimated fair value | Significant  other observable  inputs (Level 2) | Hawaiian Electric Company, Inc. and Subsidiaries | Money Market Funds
Financial assets
Money market mutual funds	$ 0		$ 0