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Retirement benefits - Additional Information (Details) - USD ($) $ in Millions |  | 12 Months Ended
--- | --- | ---
Dec. 03, 2021 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Vested percentage of interest of each affected participant after participating employer terminates participation |  | 100.00% |  |
Number of years for which regulatory asset/liability for each utility will be amortized, beginning with respective utility's next rate case |  | 5 years |  |
Executive life and nonqualified pension plan expenses |  | $ 1.2 | $ 1.1 |
Regulatory asset charges pretax |  | $ (230.8) | 53.7 |
Fair value of plan assets, valuation difference amortized in first year |  | 0.00% |  |
Fair value of plan assets, valuation difference amortized in two to five years |  | 25.00% |  |
Number of past years for adding or subtracting the unamortized differences from fair value |  | 4 years |  |
Percentage of range around fair value |  | 15.00% |  |
Expected cash funding for qualified defined benefit plans |  |  |  |
Defined contribution plan, expenses recognized |  | $ 6.0 | 7.0 | $ 7.0
Cash contributions by the employer to defined contribution plan |  | 6.0 | 7.0 | 7.0
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |  |
Expected cash funding for qualified defined benefit plans |  |  |  |
Defined contribution plan, expenses recognized |  | 3.0 | 3.0 | 3.0
Cash contributions by the employer to defined contribution plan |  | $ 3.0 | 3.0 | 3.0
Employer contribution, percent of annual compensation | 10.00% |  |  |
Pension benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Expected rate of return on plan assets |  | 7.25% |  |
Assumed discount rate, active manager premium |  | 0.20% |  |
Actual net return on plan assets |  | 13.20% |  |
Pension expense |  | $ 47.0 | 59.0 | 59.0
Expected cash funding for qualified defined benefit plans |  |  |  |
Estimate of contributions to postretirement benefit plans in next fiscal year |  | 41.0 |  |
2022 |  | 102.0 |  |
2023 |  | 105.0 |  |
2024 |  | 108.0 |  |
2025 |  | 112.0 |  |
2026 |  | 116.0 |  |
2027 through 2031 |  | $ 632.0 |  |
Pension benefits | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Actual net return on plan assets |  | 14.20% |  |
Pension expense |  | $ 47.0 | $ 55.0 | 57.0
Expected cash funding for qualified defined benefit plans |  |  |  |
Estimate of contributions to postretirement benefit plans in next fiscal year |  | 41.0 |  |
2022 |  | 93.0 |  |
2023 |  | 96.0 |  |
2024 |  | 99.0 |  |
2025 |  | 102.0 |  |
2026 |  | 106.0 |  |
2027 through 2031 |  | $ 580.0 |  |
Pension benefits | American Savings Bank (ASB) |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Expected rate of return on plan assets |  | 3.24% |  |
Other benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Assumed health care trend rate for medical in next fiscal year |  | 6.50% | 6.75% |
Assumed health care trend rate for grading down plan in 12 fiscal years thereafter |  | 5.00% |  |
Assumed health care trend rate for dental in next fiscal year |  | 5.00% | 5.00% |
Assumed health care trend rate for vision in next fiscal year |  | 4.00% | 4.00% |
Assumed health care trend rate for grading down in 2028 and thereafter |  |  | 5.00% |
Postretirement benefits other than pension expense |  | $ (0.1) | $ (0.1) | (0.1)
Expected cash funding for qualified defined benefit plans |  |  |  |
Estimate of contributions to postretirement benefit plans in next fiscal year |  | 0.0 |  |
Other benefits | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Postretirement benefits other than pension expense |  | (0.2) | $ (0.2) | $ (0.3)
Expected cash funding for qualified defined benefit plans |  |  |  |
Estimate of contributions to postretirement benefit plans in next fiscal year |  | $ 0.0 |  |
Minimum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Threshold percentage around fair value |  | 85.00% |  |
Maximum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Threshold percentage around fair value |  | 115.00% |  |

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- Definition The pretax net amount of regulatory asset charges, which would otherwise be recorded in accumulated other comprehensive income. + References No definition available. + Details
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- Definition Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Assumed Discount Rate, Active Manager Premium + References No definition available. + Details
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- Definition An assumption for the next fiscal year as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation. + References No definition available. + Details
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- Definition The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the dental plan under the defined benefit plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status. + References No definition available. + Details
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- Definition Defined Benefit Plan, Health Care Cost Trend Rate Assumed For Grading Down Plan In Nine Fiscal Years Thereafter + References No definition available. + Details
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- Definition The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the medical plan under the defined benefit plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status. + References No definition available. + Details
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- Definition The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the vision plan under the defined benefit plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status. + References No definition available. + Details
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- Definition Represents the number of years for which regulatory asset/liability for each utilities will be amortized, beginning with the respective utility's next rate case. + References No definition available. + Details
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- Definition Represents the percentage of valuation difference of plan assets amortized in the first year to determine market related value. + References No definition available. + Details
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- Definition Represents the vested percentage of interest of each affected participant if a participating employer terminates its participation in the plans up to the extent funded. + References No definition available. + Details
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- Definition The amount of pension benefit costs recognized during the period for defined benefit plans. Pension expense includes the following components: service cost, interest cost, expected return on plan assets, gain (loss) on plan assets, prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments, less the impact of Public Utilities Commission decisions and orders and capitalized amounts. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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