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Retirement benefits - Components of NPPC and NPBC (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Pension benefits      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]      
Service cost $ 45,578 $ 78,173 $ 81,432
Interest cost 103,000 80,062 75,361
Expected return on plan assets (140,824) (141,266) (132,223)
Amortization of net prior service gain 0 0 0
Amortization of net actuarial losses (gains) 669 27,412 27,245
Net periodic pension/benefit cost 8,423 44,381 51,815
Impact of PUC D&Os 71,905 37,148 27,963
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os) 80,328 81,529 79,778
Pension benefits | Hawaiian Electric Company, Inc. and Subsidiaries      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]      
Service cost 44,143 75,845 79,463
Interest cost 95,351 74,363 70,235
Expected return on plan assets (131,962) (133,873) (125,404)
Amortization of net prior service gain 0 0 0
Amortization of net actuarial losses (gains) 28 26,358 27,534
Net periodic pension/benefit cost 7,560 42,693 51,828
Impact of PUC D&Os 71,905 37,148 27,963
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os) 79,465 79,841 79,791
Other benefits      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]      
Service cost 1,430 2,580 2,827
Interest cost 8,520 6,502 6,122
Expected return on plan assets (13,648) (13,621) (12,957)
Amortization of net prior service gain (875) (928) (1,533)
Amortization of net actuarial losses (gains) (1,888) (12) 203
Net periodic pension/benefit cost (6,461) (5,479) (5,338)
Impact of PUC D&Os 5,846 4,966 4,839
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os) (615) (513) (499)
Other benefits | Hawaiian Electric Company, Inc. and Subsidiaries      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]      
Service cost 1,415 2,554 2,802
Interest cost 8,143 6,227 5,875
Expected return on plan assets (13,442) (13,381) (12,755)
Amortization of net prior service gain (872) (925) (1,530)
Amortization of net actuarial losses (gains) (1,827) 0 206
Net periodic pension/benefit cost (6,583) (5,525) (5,402)
Impact of PUC D&Os 5,846 4,966 4,839
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os) $ (737) $ (559) $ (563)