Retirement benefits (Details) - HECO (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Retirement benefits
Contributions made to defined benefit plans	$ 0
Current estimate of contributions to defined benefit plans in current fiscal year	86,000,000		78,000,000
Benefits expected to be paid directly by the company in current fiscal year, comparable to prior year	2,000,000		1,000,000
Defined benefit plans
Retirement benefits expense	11,000,000	8,000,000
Number of years for which regulatory asset/liability for each utility will be amortized, beginning with respective utility's next rate case	5 years
Defined contribution plan, expenses recognized	1,000,000	900,000
Maximum
Retirement benefits
Funded status of retirement plan (as a percent)	80.00%
Hawaiian Electric Company, Inc. and Subsidiaries
Retirement benefits
Contributions made to defined benefit plans	21,000,000	26,000,000
Current estimate of contributions to defined benefit plans in current fiscal year	84,000,000		63,000,000
Benefits expected to be paid directly by the company in current fiscal year, comparable to prior year	1,000,000	500,000
Defined benefit plans
Retirement benefits expense	10,000,000	8,000,000
Number of years for which regulatory asset/liability for each utility will be amortized, beginning with respective utility's next rate case	5 years
Defined contribution plan, expenses recognized	200,000
Pension benefits
Defined benefit plans
Service cost	14,089,000	10,191,000
Interest cost	16,106,000	16,771,000
Expected return on plan assets	(18,085,000)	(17,856,000)
Amortization of net prior service gain	(24,000)	(81,000)
Amortization of net actuarial loss	9,819,000	6,423,000
Net periodic benefit cost	21,905,000	15,448,000
Impact of PUC D&Os	(7,436,000)	(3,857,000)
Net periodic benefit cost (adjusted for impact of PUC D&Os)	14,469,000	11,591,000
Pension benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined benefit plans
Service cost	13,603,000	9,802,000
Interest cost	14,676,000	15,261,000
Expected return on plan assets	(16,090,000)	(16,060,000)
Amortization of net prior service gain	(116,000)	(172,000)
Amortization of net actuarial loss	8,790,000	5,869,000
Net periodic benefit cost	20,863,000	14,700,000
Impact of PUC D&Os	(7,436,000)	(3,857,000)
Net periodic benefit cost (adjusted for impact of PUC D&Os)	13,427,000	10,843,000
Other benefits
Defined benefit plans
Service cost	1,049,000	1,096,000
Interest cost	1,931,000	2,281,000
Expected return on plan assets	(2,562,000)	(2,621,000)
Amortization of net prior service gain	(448,000)	(448,000)
Amortization of net actuarial loss	521,000	453,000
Net periodic benefit cost	491,000	761,000
Impact of PUC D&Os	(397,000)	(680,000)
Net periodic benefit cost (adjusted for impact of PUC D&Os)	94,000	81,000
Other benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined benefit plans
Service cost	1,014,000	1,048,000
Interest cost	1,861,000	2,205,000
Expected return on plan assets	(2,520,000)	(2,579,000)
Amortization of net transition obligation		(2,000)
Amortization of net prior service gain	(451,000)	(451,000)
Amortization of net actuarial loss	504,000	440,000
Net periodic benefit cost	408,000	661,000
Impact of PUC D&Os	(397,000)	(680,000)
Net periodic benefit cost (adjusted for impact of PUC D&Os)	$ 11,000	$ (19,000)