Consolidating financial information (Details) - HECO (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Other income (loss)
Allowance for equity funds used during construction	$ 1,611	$ 1,570	$ 5,548	$ 4,131
Interest and other charges
Allowance for borrowed funds used during construction	(688)	(658)	(2,451)	(1,731)
Net income	48,177	48,875	126,239	105,422
Preferred stock dividends of subsidiaries	471	471	1,417	1,417
Net income for common stock	47,706	48,404	124,822	104,005
HECO
Operating revenues	579,464	590,014	1,677,604	1,550,491
Operating expenses
Fuel oil	248,443	259,027	724,862	662,524
Purchased power	135,507	141,742	401,423	386,414
Other operation	48,201	43,604	132,770	139,255
Maintenance	19,615	20,776	60,993	64,045
Depreciation	22,738	21,613	68,046	67,381
Taxes, other than income taxes	53,935	54,052	159,928	143,049
Income taxes	15,725	16,341	41,049	24,679
Total operating expenses	544,164	557,155	1,589,071	1,487,347
Operating income	35,300	32,859	88,533	63,144
Other income (loss)
Allowance for equity funds used during construction	1,323	1,220	4,558	3,154
Equity in earnings of subsidiaries	11,285	11,929	28,025	34,382
Other, net	913	930	3,114	2,288
Total other income	13,521	14,079	35,697	39,824
Interest and other charges
Interest on long-term debt	9,981	9,130	29,301	27,391
Amortization of net bond premium and expense	629	503	1,541	1,519
Other interest charges	142	(406)	(412)	414
Allowance for borrowed funds used during construction	(576)	(518)	(2,061)	(1,338)
Total interest and other charges	10,176	8,709	28,369	27,986
Net income	38,645	38,229	95,861	74,982
Net income attributable to HECO	38,645	38,229	95,861	74,982
Preferred stock dividends of HECO	270	270	810	810
Net income for common stock	38,375	37,959	95,051	74,172
HELCO
Operating revenues	108,490	118,420	332,558	328,650
Operating expenses
Fuel oil	25,752	31,433	88,778	90,047
Purchased power	37,693	38,252	108,996	100,516
Other operation	10,888	8,530	29,851	26,322
Maintenance	5,146	5,115	14,280	13,263
Depreciation	8,299	8,148	25,036	24,619
Taxes, other than income taxes	10,444	10,929	31,330	30,265
Income taxes	2,782	4,988	9,836	13,482
Total operating expenses	101,004	107,395	308,107	298,514
Operating income	7,486	11,025	24,451	30,136
Other income (loss)
Allowance for equity funds used during construction	148	131	433	447
Other, net	114	130	314	450
Total other income	262	261	747	897
Interest and other charges
Interest on long-term debt	2,751	2,985	8,649	8,954
Amortization of net bond premium and expense	117	137	362	417
Other interest charges	78	97	131	271
Allowance for borrowed funds used during construction	(59)	(54)	(174)	(189)
Total interest and other charges	2,887	3,165	8,968	9,453
Net income	4,861	8,121	16,230	21,580
Preferred stock dividends of subsidiaries	133	133	400	400
Net income attributable to HECO	4,728	7,988	15,830	21,180
Net income for common stock	4,728	7,988	15,830	21,180
MECO
Operating revenues	111,249	110,473	324,664	311,719
Operating expenses
Fuel oil	52,978	62,015	172,436	172,905
Purchased power	13,499	8,490	29,421	21,249
Other operation	11,352	9,281	34,185	28,757
Maintenance	5,607	6,445	16,368	15,500
Depreciation	4,904	5,222	15,474	15,673
Taxes, other than income taxes	10,471	10,374	30,891	29,188
Income taxes	3,845	2,531	7,406	8,469
Total operating expenses	102,656	104,358	306,181	291,741
Operating income	8,593	6,115	18,483	19,978
Other income (loss)
Allowance for equity funds used during construction	140	219	557	530
Other, net	47	116	304	270
Total other income	187	335	861	800
Interest and other charges
Interest on long-term debt	1,962	2,268	6,450	6,804
Amortization of net bond premium and expense	124	127	373	380
Other interest charges	94	103	253	302
Allowance for borrowed funds used during construction	(53)	(86)	(216)	(204)
Total interest and other charges	2,127	2,412	6,860	7,282
Net income	6,653	4,038	12,484	13,496
Preferred stock dividends of subsidiaries	95	95	286	286
Net income attributable to HECO	6,558	3,943	12,198	13,210
Net income for common stock	6,558	3,943	12,198	13,210
Other subsidiaries
Other income (loss)
Other, net	(1)	(2)	(3)	(8)
Total other income	(1)	(2)	(3)	(8)
Interest and other charges
Net income	(1)	(2)	(3)	(8)
Net income attributable to HECO	(1)	(2)	(3)	(8)
Net income for common stock	(1)	(2)	(3)	(8)
Consolidating adjustments
Other income (loss)
Equity in earnings of subsidiaries	(11,285)	(11,929)	(28,025)	(34,382)
Other, net	(28)	(4)	(56)	(22)
Total other income	(11,313)	(11,933)	(28,081)	(34,404)
Interest and other charges
Other interest charges	(28)	(4)	(56)	(22)
Total interest and other charges	(28)	(4)	(56)	(22)
Net income	(11,285)	(11,929)	(28,025)	(34,382)
Net income attributable to HECO	(11,285)	(11,929)	(28,025)	(34,382)
Net income for common stock	(11,285)	(11,929)	(28,025)	(34,382)
HECO Consolidated
Operating revenues	799,203	818,907	2,334,826	2,190,860
Operating expenses
Fuel oil	327,173	352,475	986,076	925,476
Purchased power	186,699	188,484	539,840	508,179
Other operation	70,441	61,415	196,806	194,334
Maintenance	30,368	32,336	91,641	92,808
Depreciation	35,941	34,983	108,556	107,673
Taxes, other than income taxes	74,850	75,355	222,149	202,502
Income taxes	22,352	23,860	58,291	46,630
Total operating expenses	747,824	768,908	2,203,359	2,077,602
Operating income	51,379	49,999	131,467	113,258
Other income (loss)
Allowance for equity funds used during construction	1,611	1,570	5,548	4,131
Other, net	1,045	1,170	3,673	2,978
Total other income	2,656	2,740	9,221	7,109
Interest and other charges
Interest on long-term debt	14,694	14,383	44,400	43,149
Amortization of net bond premium and expense	870	767	2,276	2,316
Other interest charges	286	(210)	(84)	965
Allowance for borrowed funds used during construction	(688)	(658)	(2,451)	(1,731)
Total interest and other charges	15,162	14,282	44,141	44,699
Net income	38,873	38,457	96,547	75,668
Preferred stock dividends of subsidiaries	228	228	686	686
Net income attributable to HECO	38,645	38,229	95,861	74,982
Preferred stock dividends of HECO	270	270	810	810
Net income for common stock	$ 38,375	$ 37,959	$ 95,051	$ 74,172