Consolidating financial information (Details) - HECO (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Operating expenses
Purchased power	$ 153,000	$ 165,000
Other income (loss)
Allowance for equity funds used during construction	1,215	1,940
Interest and other charges
Allowance for borrowed funds used during construction	(730)	(870)
Net income	34,152	38,789
Preferred stock dividends of subsidiaries	473	473
Net income for common stock	33,679	38,316
HECO
Operating revenues	505,829	530,613
Operating expenses
Fuel oil	221,967	235,026
Purchased power	111,155	124,780
Other operation	50,111	39,948
Maintenance	21,652	20,836
Depreciation	24,707	22,571
Taxes, other than income taxes	48,085	50,553
Income taxes	7,311	11,963
Total operating expenses	484,988	505,677
Operating income	20,841	24,936
Other income (loss)
Allowance for equity funds used during construction	983	1,581
Equity in earnings of subsidiaries	10,985	8,490
Other, net	2,021	1,094
Income tax benefits (expense)	(230)	(30)
Total other income	13,759	11,135
Interest and other charges
Interest on long-term debt	9,902	9,130
Amortization of net bond premium and expense	410	483
Other interest charges	157	(387)
Allowance for borrowed funds used during construction	(568)	(725)
Total interest and other charges	9,901	8,501
Net income	24,699	27,570
Net income attributable to HECO	24,699	27,570
Preferred stock dividends of HECO	270	270
Net income for common stock	24,429	27,300
HELCO
Operating revenues	106,016	112,327
Operating expenses
Fuel oil	32,936	32,410
Purchased power	30,122	33,908
Other operation	11,064	9,015
Maintenance	3,806	4,249
Depreciation	8,547	8,436
Taxes, other than income taxes	9,686	10,463
Income taxes	2,714	4,223
Total operating expenses	98,875	102,704
Operating income	7,141	9,623
Other income (loss)
Allowance for equity funds used during construction	138	125
Other, net	142	116
Income tax benefits (expense)	(23)	(15)
Total other income	257	226
Interest and other charges
Interest on long-term debt	2,750	2,985
Amortization of net bond premium and expense	117	137
Other interest charges	69	33
Allowance for borrowed funds used during construction	(92)	(51)
Total interest and other charges	2,844	3,104
Net income	4,554	6,745
Preferred stock dividends of subsidiaries	134	134
Net income attributable to HECO	4,420	6,611
Net income for common stock	4,420	6,611
MECO
Operating revenues	104,352	104,998
Operating expenses
Fuel oil	50,197	60,403
Purchased power	12,087	6,101
Other operation	10,248	12,886
Maintenance	4,244	4,953
Depreciation	5,026	5,475
Taxes, other than income taxes	9,916	9,979
Income taxes	4,070	1,179
Total operating expenses	95,788	100,976
Operating income	8,564	4,022
Other income (loss)
Allowance for equity funds used during construction	94	234
Other, net	177	110
Income tax benefits (expense)	(46)	1
Total other income	225	345
Interest and other charges
Interest on long-term debt	1,962	2,268
Amortization of net bond premium and expense	120	125
Other interest charges	117	93
Allowance for borrowed funds used during construction	(70)	(94)
Total interest and other charges	2,129	2,392
Net income	6,660	1,975
Preferred stock dividends of subsidiaries	95	95
Net income attributable to HECO	6,565	1,880
Net income for common stock	6,565	1,880
Other subsidiaries
Other income (loss)
Other, net		(1)
Total other income		(1)
Interest and other charges
Net income		(1)
Net income attributable to HECO		(1)
Net income for common stock		(1)
Consolidating adjustments
Other income (loss)
Equity in earnings of subsidiaries	(10,985)	(8,490)
Other, net	(28)	(10)
Total other income	(11,013)	(8,500)
Interest and other charges
Other interest charges	(28)	(10)
Total interest and other charges	(28)	(10)
Net income	(10,985)	(8,490)
Net income attributable to HECO	(10,985)	(8,490)
Net income for common stock	(10,985)	(8,490)
HECO Consolidated
Operating revenues	716,197	747,938
Operating expenses
Fuel oil	305,100	327,839
Purchased power	153,364	164,789
Other operation	71,423	61,849
Maintenance	29,702	30,038
Depreciation	38,280	36,482
Taxes, other than income taxes	67,687	70,995
Income taxes	14,095	17,365
Total operating expenses	679,651	709,357
Operating income	36,546	38,581
Other income (loss)
Allowance for equity funds used during construction	1,215	1,940
Other, net	2,312	1,309
Income tax benefits (expense)	(299)	(44)
Total other income	3,228	3,205
Interest and other charges
Interest on long-term debt	14,614	14,383
Amortization of net bond premium and expense	647	745
Other interest charges	315	(271)
Allowance for borrowed funds used during construction	(730)	(870)
Total interest and other charges	14,846	13,987
Net income	24,928	27,799
Preferred stock dividends of subsidiaries	229	229
Net income attributable to HECO	24,699	27,570
Preferred stock dividends of HECO	270	270
Net income for common stock	$ 24,429	$ 27,300