Retirement benefits Additional Information (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2007
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	$ 1,200,000	$ 1,200,000
Regulatory asset charges pretax	340,000,000	(364,000,000)
Fair value of plan assets, valuation difference amortized in first year (as a percent)	0.00%
Fair value of plan assets, valuation difference amortized in two to five years (as a percent)	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	5,000,000	5,000,000	4,000,000
Cash contributions by the employer to defined contribution plan	5,000,000	4,000,000	4,000,000
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%
Hawaiian Electric Company, Inc. and Subsidiaries
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	833,843,000	506,186,000
Retirement benefits expense	32,000,000	30,000,000	32,000,000
Expected cash funding for qualified defined benefit plans
Maximum percentage of participant deferrals eligible for Employer contribution match, towards defined contribution plan	6.00%
Employer's additional matching contribution on employee deferrals (as a percent)	50.00%
Defined contribution plan, expenses recognized	900,000	600,000
American Savings Bank (ASB)
Expected cash funding for qualified defined benefit plans
Maximum percentage of participant deferrals eligible for Employer contribution match, towards defined contribution plan	4.00%
Hawaii Electric Light Company, Inc. (HELCO)
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	107,454,000	64,552,000		12,800,000
Regulatory assets recovery period	5 years
Hawaiian Electric Company, Inc (HECO)
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	623,784,000	381,346,000
Value of plan assets requiring more than minimum level contributions required by law				0
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets (as a percent)	7.75%
Discount rate (as a percent)	4.22%	5.09%	4.13%
Pension expense	32,000,000	34,000,000	35,000,000
Defined benefit pension plans with accumulated benefit obligations in excess of plan assets
Aggregate accumulated benefit obligations	1,500,000,000	1,200,000,000
Plan assets	1,200,000,000	1,100,000,000
Defined benefit plans with benefit obligations in excess of plan assets
Aggregate projected benefit obligations	1,700,000,000	1,400,000,000
Plan assets	1,200,000,000	1,100,000,000
Expected cash funding for qualified defined benefit plans
Estimate of contributions to postretirement benefit plans in 2015	85,000,000	0
Pension benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined Benefit Plan Disclosure [Line Items]
Pension expense	31,000,000	30,000,000	32,000,000
Defined benefit pension plans with accumulated benefit obligations in excess of plan assets
Aggregate accumulated benefit obligations	1,500,000,000	1,200,000,000
Plan assets	1,100,000,000	1,100,000,000
Expected cash funding for qualified defined benefit plans
Estimate of contributions to postretirement benefit plans in 2015	83,000,000
Other benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate (as a percent)	4.17%	5.03%	4.07%
Assumed health care trend rate for medical in next fiscal year (as a percent)	7.25%	7.50%
Assumed health care trend rate for grading down in 2024 and thereafter (as a percent)	5.00%	5.00%
Assumed health care trend rate for dental in next fiscal year (as a percent)	5.00%	5.00%
Assumed health care trend rate for vision in next fiscal year (as a percent)	4.00%	4.00%
Age threshold health care trend rates are adjusted	65 years
Percentage by which medical trend for post-65 is higher than pre-65, 2014	4.00%
Percentage by which medical trend for post-65 is higher than pre-65, 2015	3.00%
Postretirement benefits other than pension expense	1,200,000	400,000	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	200,000
Effect of one-percentage-point increase in assumed health care cost trend rates that would have increased the accumulated postretirement benefit obligation (APBO)	3,800,000
Effect of one-percentage-point decrease that would have reduced total service and interest cost	300,000
Effect of one-percentage-point decrease that would have reduced APBO	4,600,000
Defined benefit pension plans with accumulated benefit obligations in excess of plan assets
Aggregate accumulated benefit obligations		400,000
Expected cash funding for qualified defined benefit plans
Estimate of contributions to postretirement benefit plans in 2015	500,000
2015	76,000,000
2016	79,000,000
2017	83,000,000
2018	87,000,000
2019	91,000,000
2020 through 2024	520,000,000
Other benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits other than pension expense	1,000,000	0	400,000
Effect of one-percentage-point increase in assumed health care cost trend rates that would have increased total service and interest cost	200,000
Effect of one-percentage-point increase in assumed health care cost trend rates that would have increased the accumulated postretirement benefit obligation (APBO)	3,700,000
Effect of one-percentage-point decrease that would have reduced total service and interest cost	300,000
Effect of one-percentage-point decrease that would have reduced APBO	4,500,000
Expected cash funding for qualified defined benefit plans
Estimate of contributions to postretirement benefit plans in 2015	500,000
2015	70,000,000
2016	73,000,000
2017	76,000,000
2018	79,000,000
2019	83,000,000
2020 through 2024	$ 476,000,000