Consolidating financial information (Details) - HECO (USD $) In Thousands, unless otherwise specified	0 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Operating expenses
Purchased power		$ 195,000	$ 187,000	$ 527,000	$ 540,000
Other income (loss)
Allowance for equity funds used during construction		1,255	1,611	4,030	5,548
Interest and other charges
Allowance for borrowed funds used during construction		(498)	(688)	(1,626)	(2,451)
Net income		48,707	48,177	123,920	126,239
Preferred stock dividends of subsidiaries		471	471	1,417	1,417
Net income for common stock		48,236	47,706	122,503	124,822
HECO
Operating revenues	5,300	547,310	579,464	1,574,869	1,677,604
Operating expenses
Fuel oil		206,478	248,443	631,824	724,862
Purchased power		143,280	135,507	389,706	401,423
Other operation		51,023	48,201	149,218	132,770
Maintenance		19,619	19,615	60,922	60,993
Depreciation		25,442	22,738	75,150	68,046
Taxes, other than income taxes		51,712	53,935	149,084	159,928
Income taxes		13,556	15,725	33,753	41,049
Total operating expenses		511,110	544,164	1,489,657	1,589,071
Operating income		36,200	35,300	85,212	88,533
Other income (loss)
Allowance for equity funds used during construction		914	1,323	3,144	4,558
Equity in earnings of subsidiaries		10,794	11,285	30,446	28,025
Other, net		795	950	3,518	3,215
Income tax benefits (expense)		(77)	(37)	(266)	(101)
Total other income		12,426	13,521	36,842	35,697
Interest and other charges
Interest on long-term debt		9,902	9,981	29,705	29,301
Amortization of net bond premium and expense		410	629	1,231	1,541
Other interest charges (credits)		585	142	637	(412)
Allowance for borrowed funds used during construction		(358)	(576)	(1,268)	(2,061)
Total interest and other charges		10,539	10,176	30,305	28,369
Net income		38,087	38,645	91,749	95,861
Net income attributable to HECO		38,087	38,645	91,749	95,861
Preferred stock dividends of HECO		270	270	810	810
Net income for common stock		37,817	38,375	90,939	95,051
HELCO
Operating revenues		107,924	108,490	320,314	332,558
Operating expenses
Fuel oil		27,615	25,752	94,120	88,778
Purchased power		34,480	37,693	93,880	108,996
Other operation		11,057	10,888	32,267	29,851
Maintenance		5,680	5,146	13,787	14,280
Depreciation		8,547	8,299	25,641	25,036
Taxes, other than income taxes		10,448	10,444	30,094	31,330
Income taxes		1,991	2,782	7,765	9,836
Total operating expenses		99,818	101,004	297,554	308,107
Operating income		8,106	7,486	22,760	24,451
Other income (loss)
Allowance for equity funds used during construction		222	148	552	433
Other, net		217	128	526	361
Income tax benefits (expense)		(32)	(14)	(73)	(47)
Total other income		407	262	1,005	747
Interest and other charges
Interest on long-term debt		2,751	2,751	8,252	8,649
Amortization of net bond premium and expense		116	117	350	362
Other interest charges (credits)		160	78	245	131
Allowance for borrowed funds used during construction		(91)	(59)	(226)	(174)
Total interest and other charges		2,936	2,887	8,621	8,968
Net income		5,577	4,861	15,144	16,230
Preferred stock dividends of subsidiaries		133	133	400	400
Net income attributable to HECO		5,444	4,728	14,744	15,830
Net income for common stock		5,444	4,728	14,744	15,830
MECO
Operating revenues		108,699	111,249	313,740	324,664
Operating expenses
Fuel oil		49,267	52,978	151,794	172,436
Purchased power		17,101	13,499	43,083	29,421
Other operation		9,928	11,352	28,130	34,185
Maintenance		6,214	5,607	13,846	16,368
Depreciation		5,006	4,904	15,074	15,474
Taxes, other than income taxes		10,222	10,471	29,650	30,891
Income taxes		3,381	3,845	9,838	7,406
Total operating expenses		101,119	102,656	291,415	306,181
Operating income		7,580	8,593	22,325	18,483
Other income (loss)
Allowance for equity funds used during construction		119	140	334	557
Other, net		124	38	412	293
Income tax benefits (expense)		(20)	9	(81)	11
Total other income		223	187	665	861
Interest and other charges
Interest on long-term debt		1,962	1,962	5,886	6,450
Amortization of net bond premium and expense		120	124	359	373
Other interest charges (credits)		324	94	887	253
Allowance for borrowed funds used during construction		(49)	(53)	(132)	(216)
Total interest and other charges		2,357	2,127	7,000	6,860
Net income		5,446	6,653	15,990	12,484
Preferred stock dividends of subsidiaries		95	95	286	286
Net income attributable to HECO		5,351	6,558	15,704	12,198
Net income for common stock		5,351	6,558	15,704	12,198
Other subsidiaries
Other income (loss)
Other, net		(1)	(1)	(2)	(3)
Total other income		(1)	(1)	(2)	(3)
Interest and other charges
Net income		(1)	(1)	(2)	(3)
Net income attributable to HECO		(1)	(1)	(2)	(3)
Net income for common stock		(1)	(1)	(2)	(3)
Consolidating adjustments
Other income (loss)
Equity in earnings of subsidiaries		(10,794)	(11,285)	(30,446)	(28,025)
Other, net		(36)	(28)	(103)	(56)
Total other income		(10,830)	(11,313)	(30,549)	(28,081)
Interest and other charges
Other interest charges (credits)		(36)	(28)	(103)	(56)
Total interest and other charges		(36)	(28)	(103)	(56)
Net income		(10,794)	(11,285)	(30,446)	(28,025)
Net income attributable to HECO		(10,794)	(11,285)	(30,446)	(28,025)
Net income for common stock		(10,794)	(11,285)	(30,446)	(28,025)
HECO Consolidated
Operating revenues		763,933	799,203	2,208,923	2,334,826
Operating expenses
Fuel oil		283,360	327,173	877,738	986,076
Purchased power		194,861	186,699	526,669	539,840
Other operation		72,008	70,441	209,615	196,806
Maintenance		31,513	30,368	88,555	91,641
Depreciation		38,995	35,941	115,865	108,556
Taxes, other than income taxes		72,382	74,850	208,828	222,149
Income taxes		18,928	22,352	51,356	58,291
Total operating expenses		712,047	747,824	2,078,626	2,203,359
Operating income		51,886	51,379	130,297	131,467
Other income (loss)
Allowance for equity funds used during construction		1,255	1,611	4,030	5,548
Other, net		1,099	1,087	4,351	3,810
Income tax benefits (expense)		(129)	(42)	(420)	(137)
Total other income		2,225	2,656	7,961	9,221
Interest and other charges
Interest on long-term debt		14,615	14,694	43,843	44,400
Amortization of net bond premium and expense		646	870	1,940	2,276
Other interest charges (credits)		1,033	286	1,666	(84)
Allowance for borrowed funds used during construction		(498)	(688)	(1,626)	(2,451)
Total interest and other charges		15,796	15,162	45,823	44,141
Net income		38,315	38,873	92,435	96,547
Preferred stock dividends of subsidiaries		228	228	686	686
Net income attributable to HECO		38,087	38,645	91,749	95,861
Preferred stock dividends of HECO		270	270	810	810
Net income for common stock		$ 37,817	$ 38,375	$ 90,939	$ 95,051