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Retirement benefits - Additional Information (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
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 | $ 1,000,000 | $ 1,100,000 |
Regulatory asset charges pretax | $ 11,200,000 | (128,000,000) |
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 | $ 7,000,000 | 7,000,000 | $ 5,000,000
Cash contributions by the employer to defined contribution plan | 7,000,000 | 6,000,000 | 5,000,000
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Expected cash funding for qualified defined benefit plans |  |  |
Defined contribution plan, expenses recognized | $ 2,300,000 | 2,000,000 | 1,500,000
Pension benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Expected rate of return on plan assets | 7.25% |  |
Discount rate | 4.51% |  |
Assumed discount rate, active manager premium | 0.20% |  |
Pension expense | $ 59,000,000 | 33,000,000 | 33,000,000
Defined benefit pension plans with accumulated benefit obligations in excess of plan assets |  |  |
Defined benefit plans - ABOs | 1,700,000,000 | 1,800,000,000 |
Aggregate accumulated benefit obligations | 1,600,000,000 | 1,700,000,000 |
Plan assets | 1,400,000,000 | 1,500,000,000 |
Defined benefit plans with benefit obligations in excess of plan assets |  |  |
PBOs | 1,900,000,000 | 2,000,000,000 |
Plan assets | 1,400,000,000 | 1,500,000,000 |
Expected cash funding for qualified defined benefit plans |  |  |
Estimate of contributions to postretirement benefit plans in 2018 | $ 47,000,000 |  |
Pension benefits | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actual net return on plan assets | 6.50% |  |
Pension expense | $ 55,000,000 | 30,000,000 | 30,000,000
Defined benefit pension plans with accumulated benefit obligations in excess of plan assets |  |  |
Defined benefit plans - ABOs | 1,600,000,000 | 1,700,000,000 |
Aggregate accumulated benefit obligations | 1,600,000,000 | 1,700,000,000 |
Plan assets | 1,300,000,000 | 1,500,000,000 |
Defined benefit plans with benefit obligations in excess of plan assets |  |  |
PBOs | 1,800,000,000 | 1,900,000,000 |
Plan assets | 1,300,000,000 | $ 1,500,000,000 |
Expected cash funding for qualified defined benefit plans |  |  |
Estimate of contributions to postretirement benefit plans in 2018 | $ 47,000,000 |  |
Other benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Assumed health care trend rate for medical in next fiscal year | 7.25% | 7.50% |
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 | $ 1,000,000 | 1,000,000
Effect of one-percentage-point increase in assumed health care cost trend rates that would have increased total service and interest cost | 100,000 |  |
Effect of one-percentage-point increase in assumed health care cost trend rates that would have increased the accumulated postretirement benefit obligation (APBO) | 2,900,000 |  |
Effect of one-percentage-point decrease that would have reduced total service and interest cost | 100,000 |  |
Effect of one-percentage-point decrease that would have reduced APBO | 3,300,000 |  |
Expected cash funding for qualified defined benefit plans |  |  |
Estimate of contributions to postretirement benefit plans in 2018 | 0 |  |
2019 | 88,000,000 |  |
2020 | 91,000,000 |  |
2021 | 95,000,000 |  |
2022 | 99,000,000 |  |
2023 | 103,000,000 |  |
2024 through 2028 | 574,000,000 |  |
Other benefits | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits other than pension expense | (100,000) | $ 800,000 | $ 700,000
Effect of one-percentage-point increase in assumed health care cost trend rates that would have increased total service and interest cost | 100,000 |  |
Effect of one-percentage-point increase in assumed health care cost trend rates that would have increased the accumulated postretirement benefit obligation (APBO) | 2,800,000 |  |
Effect of one-percentage-point decrease that would have reduced total service and interest cost | 100,000 |  |
Effect of one-percentage-point decrease that would have reduced APBO | 3,200,000 |  |
Expected cash funding for qualified defined benefit plans |  |  |
Estimate of contributions to postretirement benefit plans in 2018 | 0 |  |
2019 | 81,000,000 |  |
2020 | 83,000,000 |  |
2021 | 87,000,000 |  |
2022 | 90,000,000 |  |
2023 | 93,000,000 |  |
2024 through 2028 | $ 525,000,000 |  |
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 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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Namespace Prefix: |
Data Type: | na
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Period Type: |

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Data Type: | na
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Period Type: |

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