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Retirement benefits - Changes in Projected Benefit Obligations and Fair Value of Plan Assets and Amounts Recognized in OCI (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Defined benefit pension and other postretirement benefit plans liability | $ (321,780) | $ (530,532) |
Pension benefits |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit obligation, balance at the beginning of the period | 2,624,530 | 2,278,283 |
Service cost | 81,432 | 73,387 | $ 62,135
Interest cost | 75,361 | 81,335 | 84,267
Actuarial (gains) losses | (43,300) | 275,973 |
Participants contributions | 0 | 0 |
Benefits paid and expenses | (93,384) | (84,448) |
Benefit obligation, balance at the end of the period | 2,644,639 | 2,624,530 | 2,278,283
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Fair value of plan assets, balance at the beginning of the period | 2,089,491 | 1,799,200 |
Actual return on plan assets | 271,443 | 302,566 |
Employer contributions | 51,777 | 70,844 |
Participants contributions | 0 | 0 |
Benefits paid and expenses | (91,966) | (83,119) |
Fair value of plan assets, balance at the end of the period | 2,320,745 | 2,089,491 | 1,799,200
Accrued benefit asset (liability), balance | (323,894) | (535,039) |
Other assets | 23,675 | 25,851 |
Defined benefit pension and other postretirement benefit plans liability | (347,569) | (560,890) |
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income [Roll Forward] |  |  |
AOCI debit/(credit), balance at beginning of the period (excluding impact of PUC D&Os) | 557,564 | 503,821 |
Recognized during year – prior service credit (cost) | 0 | (8) |
Recognized during year – net actuarial loss | (27,245) | (33,456) |
Occurring during year – net actuarial loss (gain) | (182,520) | 87,207 |
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os) | 347,799 | 557,564 | 503,821
Cumulative impact of PUC D&Os | (324,162) | (534,594) |
AOCI debit/(credit), balance at end of the period | 23,637 | 22,970 |
Net actuarial loss (gain) | 347,799 | 557,564 |
Prior service gain | 0 | 0 |
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os) | 347,799 | 557,564 | 503,821
Income taxes (benefits) | (6,199) | (5,988) |
AOCI debit/(credit), net of taxes (benefits) balance at the end of the period | 17,438 | 16,982 |
Pension benefits | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit obligation, balance at the beginning of the period | 2,440,758 | 2,110,904 |
Service cost | 79,463 | 71,604 | 60,461
Interest cost | 70,235 | 75,484 | 77,851
Actuarial (gains) losses | (39,755) | 260,102 |
Participants contributions | 0 | 0 |
Benefits paid and expenses | (85,425) | (77,336) |
Transfers | (332) | 0 |
Benefit obligation, balance at the end of the period | 2,464,944 | 2,440,758 | 2,110,904
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Fair value of plan assets, balance at the beginning of the period | 1,909,730 | 1,640,417 |
Actual return on plan assets | 266,922 | 276,453 |
Employer contributions | 51,079 | 69,720 |
Participants contributions | 0 | 0 |
Benefits paid and expenses | (84,852) | (76,860) |
Other | (262) | 0 |
Fair value of plan assets, balance at the end of the period | 2,142,617 | 1,909,730 | 1,640,417
Accrued benefit asset (liability), balance | (322,327) | (531,028) |
Other assets | 0 | 0 |
Other liabilities (short-term) | (547) | (535) |
Defined benefit pension and other postretirement benefit plans liability | (321,780) | (530,493) |
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income [Roll Forward] |  |  |
AOCI debit/(credit), balance at beginning of the period (excluding impact of PUC D&Os) | 538,521 | 478,078 |
Recognized during year – prior service credit (cost) | 0 | (9) |
Recognized during year – net actuarial loss | (27,534) | (30,566) |
Occurring during year – net actuarial loss (gain) | (181,342) | 91,018 |
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os) | 329,645 | 538,521 | 478,078
Cumulative impact of PUC D&Os | (324,162) | (534,594) |
AOCI debit/(credit), balance at end of the period | 5,483 | 3,927 |
Net actuarial loss (gain) | 329,645 | 538,521 |
Prior service gain | 0 | 0 |
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os) | 329,645 | 538,521 | 478,078
Income taxes (benefits) | (1,412) | (1,011) |
AOCI debit/(credit), net of taxes (benefits) balance at the end of the period | 4,071 | 2,916 |
Other benefits |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit obligation, balance at the beginning of the period | 226,421 | 215,639 |
Service cost | 2,827 | 2,537 | 2,209
Interest cost | 6,122 | 7,407 | 8,004
Actuarial (gains) losses | (8,527) | 9,785 |
Participants contributions | 2,943 | 2,768 |
Benefits paid and expenses | (11,635) | (11,715) |
Benefit obligation, balance at the end of the period | 218,151 | 226,421 | 215,639
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Fair value of plan assets, balance at the beginning of the period | 219,873 | 200,831 |
Actual return on plan assets | 28,130 | 27,678 |
Employer contributions | 0 | 0 |
Participants contributions | 2,943 | 2,768 |
Benefits paid and expenses | (11,635) | (11,404) |
Fair value of plan assets, balance at the end of the period | 239,311 | 219,873 | 200,831
Accrued benefit asset (liability), balance | 21,160 | (6,548) |
Other assets | 21,663 | 0 |
Defined benefit pension and other postretirement benefit plans liability | (503) | (6,548) |
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income [Roll Forward] |  |  |
AOCI debit/(credit), balance at beginning of the period (excluding impact of PUC D&Os) | 2,395 | 6,610 |
Recognized during year – prior service credit (cost) | 1,533 | 1,761 |
Recognized during year – net actuarial loss | (203) | (208) |
Occurring during year – net actuarial loss (gain) | (23,700) | (5,768) |
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os) | (19,975) | 2,395 | 6,610
Cumulative impact of PUC D&Os | 19,166 | (1,177) |
AOCI debit/(credit), balance at end of the period | (809) | 1,218 |
Net actuarial loss (gain) | (18,172) | 5,731 |
Prior service gain | (1,803) | (3,336) |
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os) | (19,975) | 2,395 | 6,610
Income taxes (benefits) | 209 | (313) |
AOCI debit/(credit), net of taxes (benefits) balance at the end of the period | (600) | 905 |
Other benefits | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit obligation, balance at the beginning of the period | 217,074 | 207,073 |
Service cost | 2,802 | 2,515 | 2,191
Interest cost | 5,875 | 7,103 | 7,673
Actuarial (gains) losses | (7,779) | 9,151 |
Participants contributions | 2,886 | 2,717 |
Benefits paid and expenses | (11,388) | (11,485) |
Transfers | 0 | 0 |
Benefit obligation, balance at the end of the period | 209,470 | 217,074 | 207,073
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Fair value of plan assets, balance at the beginning of the period | 216,315 | 197,564 |
Actual return on plan assets | 27,712 | 27,207 |
Employer contributions | 0 | 0 |
Participants contributions | 2,886 | 2,717 |
Benefits paid and expenses | (11,388) | (11,173) |
Other | 0 | 0 |
Fair value of plan assets, balance at the end of the period | 235,525 | 216,315 | 197,564
Accrued benefit asset (liability), balance | 26,055 | (759) |
Other assets | 26,055 | 0 |
Other liabilities (short-term) | 0 | (720) |
Defined benefit pension and other postretirement benefit plans liability | 0 | (39) |
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income [Roll Forward] |  |  |
AOCI debit/(credit), balance at beginning of the period (excluding impact of PUC D&Os) | 1,181 | 5,730 |
Recognized during year – prior service credit (cost) | 1,530 | 1,758 |
Recognized during year – net actuarial loss | (206) | (207) |
Occurring during year – net actuarial loss (gain) | (22,736) | (6,100) |
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os) | (20,231) | 1,181 | 5,730
Cumulative impact of PUC D&Os | 19,166 | (1,177) |
AOCI debit/(credit), balance at end of the period | (1,065) | 4 |
Net actuarial loss (gain) | (18,434) | 4,508 |
Prior service gain | (1,797) | (3,327) |
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os) | (20,231) | 1,181 | $ 5,730
Income taxes (benefits) | 274 | (1) |
AOCI debit/(credit), net of taxes (benefits) balance at the end of the period | $ (791) | $ 3 |

X
- Definition Represents the beginning and ending balance of accumulated other comprehensive income related to retirement benefit plans, excluding the impact of public utilities commission decision and orders. + References No definition available. + Details
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- Definition The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment and other expenses. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations. + References No definition available. + Details
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- Definition The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment and other expenses. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets. + References No definition available. + Details
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- Definition Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=124509347&loc=SL7669686-108580 + Details
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- Definition Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921 + Details
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- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 7: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 + Details
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