Fair value measurements - Fair Value Hierarchy of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Financial assets
Derivative asset, statement of financial position	Other	Other
Financial liabilities
Derivative liability, statement of financial position		Other
Carrying or notional amount
Financial assets
Derivative assets	$ 29,312	$ 10,634
Financial liabilities
Short-term borrowings	48,623
Derivative liabilities		22,949
Long-term debt, net	2,799,558	2,842,429
Carrying or notional amount | Money market mutual funds
Financial assets
Money market mutual funds	1,162,259	226,085
Carrying or notional amount | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Short-term borrowings	48,623
Long-term debt, net	1,901,214	1,934,277
Carrying or notional amount | Hawaiian Electric Company, Inc. and Subsidiaries | Money market mutual funds
Financial assets
Money market mutual funds	115,599	85,807
Estimated fair value
Financial assets
Derivative assets	1,629	972
Financial liabilities
Short-term borrowings	48,623
Derivative liabilities		303
Long-term debt, net	2,196,403	2,133,225
Estimated fair value | Money market mutual funds
Financial assets
Money market mutual funds	1,162,259	226,085
Estimated fair value | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Short-term borrowings	48,623
Long-term debt, net	1,446,316	1,385,025
Estimated fair value | Hawaiian Electric Company, Inc. and Subsidiaries | Money market mutual funds
Financial assets
Money market mutual funds	115,599	85,807
Estimated fair value | Quoted prices in active markets for identical assets (Level 1)
Financial assets
Derivative assets	0	0
Financial liabilities
Short-term borrowings	0
Derivative liabilities		0
Long-term debt, net	0	0
Estimated fair value | Quoted prices in active markets for identical assets (Level 1) | Money market mutual funds
Financial assets
Money market mutual funds	1,162,259	226,085
Estimated fair value | Quoted prices in active markets for identical assets (Level 1) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Short-term borrowings	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 mutual funds
Financial assets
Money market mutual funds	115,599	85,807
Estimated fair value | Significant other observable inputs (Level 2)
Financial assets
Derivative assets	1,629	972
Financial liabilities
Short-term borrowings	48,623
Derivative liabilities		303
Long-term debt, net	2,196,403	2,133,225
Estimated fair value | Significant other observable inputs (Level 2) | Money market mutual 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	48,623
Long-term debt, net	1,446,316	1,385,025
Estimated fair value | Significant other observable inputs (Level 2) | Hawaiian Electric Company, Inc. and Subsidiaries | Money market mutual funds
Financial assets
Money market mutual funds	0	0
Estimated fair value | Significant unobservable inputs (Level 3)
Financial assets
Derivative assets	0	0
Financial liabilities
Short-term borrowings	0
Derivative liabilities		0
Long-term debt, net	0	0
Estimated fair value | Significant unobservable inputs (Level 3) | Money market mutual funds
Financial assets
Money market mutual funds	0	0
Estimated fair value | Significant unobservable inputs (Level 3) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Short-term borrowings	0
Long-term debt, net	0	0
Estimated fair value | Significant unobservable inputs (Level 3) | Hawaiian Electric Company, Inc. and Subsidiaries | Money market mutual funds
Financial assets
Money market mutual funds	$ 0	$ 0