Consolidating financial information (Details) - HECO (USD $) In Thousands, unless otherwise specified	0 Months Ended	3 Months Ended		6 Months Ended
	May 31, 2013	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Operating expenses
Purchased power		$ 178,000	$ 188,000	$ 332,000	$ 353,000
Other income (loss)
Allowance for equity funds used during construction		1,560	1,997	2,775	3,937
Interest and other charges
Allowance for borrowed funds used during construction		(398)	(893)	(1,128)	(1,763)
Net income		41,061	39,273	75,213	78,062
Preferred stock dividends of subsidiaries		473	473	946	946
Net income for common stock		40,588	38,800	74,267	77,116
HECO
Operating revenues	5,300	521,730	567,527	1,027,559	1,098,140
Operating expenses
Fuel oil		203,379	241,393	425,346	476,419
Purchased power		135,271	141,136	246,426	265,916
Other operation		48,084	44,621	98,195	84,569
Maintenance		19,651	20,542	41,303	41,378
Depreciation		25,001	22,737	49,708	45,308
Taxes, other than income taxes		49,287	55,440	97,372	105,993
Income taxes		12,886	13,361	20,197	25,324
Total operating expenses		493,559	539,230	978,547	1,044,907
Operating income		28,171	28,297	49,012	53,233
Other income (loss)
Allowance for equity funds used during construction		1,247	1,654	2,230	3,235
Equity in earnings of subsidiaries		8,667	8,250	19,652	16,740
Other, net		702	1,173	2,723	2,266
Income tax benefits (expense)		41	(36)	(189)	(65)
Total other income		10,657	11,041	24,416	22,176
Interest and other charges
Interest on long-term debt		9,901	10,190	19,803	19,320
Amortization of net bond premium and expense		411	429	821	912
Other interest charges (credits)		(105)	(167)	52	(554)
Allowance for borrowed funds used during construction		(342)	(760)	(910)	(1,485)
Total interest and other charges		9,865	9,692	19,766	18,193
Net income		28,963	29,646	53,662	57,216
Net income attributable to HECO		28,963	29,646	53,662	57,216
Preferred stock dividends of HECO		270	270	540	540
Net income for common stock		28,693	29,376	53,122	56,676
HELCO
Operating revenues		106,374	111,741	212,390	224,068
Operating expenses
Fuel oil		33,569	30,616	66,505	63,026
Purchased power		29,278	37,395	59,400	71,303
Other operation		10,146	9,948	21,210	18,963
Maintenance		4,301	4,885	8,107	9,134
Depreciation		8,547	8,301	17,094	16,737
Taxes, other than income taxes		9,960	10,423	19,646	20,886
Income taxes		3,060	2,831	5,774	7,054
Total operating expenses		98,861	104,399	197,736	207,103
Operating income		7,513	7,342	14,654	16,965
Other income (loss)
Allowance for equity funds used during construction		192	160	330	285
Other, net		167	117	309	232
Income tax benefits (expense)		(18)	(18)	(41)	(32)
Total other income		341	259	598	485
Interest and other charges
Interest on long-term debt		2,751	2,913	5,501	5,898
Amortization of net bond premium and expense		117	108	234	245
Other interest charges (credits)		16	20	85	53
Allowance for borrowed funds used during construction		(43)	(64)	(135)	(115)
Total interest and other charges		2,841	2,977	5,685	6,081
Net income		5,013	4,624	9,567	11,369
Preferred stock dividends of subsidiaries		133	133	267	267
Net income attributable to HECO		4,880	4,491	9,300	11,102
Net income for common stock		4,880	4,491	9,300	11,102
MECO
Operating revenues		100,689	108,417	205,041	213,415
Operating expenses
Fuel oil		52,330	59,055	102,527	119,458
Purchased power		13,895	9,821	25,982	15,922
Other operation		7,954	9,947	18,202	22,833
Maintenance		3,388	5,808	7,632	10,761
Depreciation		5,042	5,095	10,068	10,570
Taxes, other than income taxes		9,512	10,441	19,428	20,420
Income taxes		2,387	2,382	6,457	3,561
Total operating expenses		94,508	102,549	190,296	203,525
Operating income		6,181	5,868	14,745	9,890
Other income (loss)
Allowance for equity funds used during construction		121	183	215	417
Other, net		111	144	288	255
Income tax benefits (expense)		(15)	2	(61)	2
Total other income		217	329	442	674
Interest and other charges
Interest on long-term debt		1,962	2,220	3,924	4,488
Amortization of net bond premium and expense		119	124	239	249
Other interest charges (credits)		446	66	563	159
Allowance for borrowed funds used during construction		(13)	(69)	(83)	(163)
Total interest and other charges		2,514	2,341	4,643	4,733
Net income		3,884	3,856	10,544	5,831
Preferred stock dividends of subsidiaries		96	96	191	191
Net income attributable to HECO		3,788	3,760	10,353	5,640
Net income for common stock		3,788	3,760	10,353	5,640
Other subsidiaries
Other income (loss)
Other, net		(1)	(1)	(1)	(2)
Total other income		(1)	(1)	(1)	(2)
Interest and other charges
Net income		(1)	(1)	(1)	(2)
Net income attributable to HECO		(1)	(1)	(1)	(2)
Net income for common stock		(1)	(1)	(1)	(2)
Consolidating adjustments
Other income (loss)
Equity in earnings of subsidiaries		(8,667)	(8,250)	(19,652)	(16,740)
Other, net		(39)	(18)	(67)	(28)
Total other income		(8,706)	(8,268)	(19,719)	(16,768)
Interest and other charges
Other interest charges (credits)		(39)	(18)	(67)	(28)
Total interest and other charges		(39)	(18)	(67)	(28)
Net income		(8,667)	(8,250)	(19,652)	(16,740)
Net income attributable to HECO		(8,667)	(8,250)	(19,652)	(16,740)
Net income for common stock		(8,667)	(8,250)	(19,652)	(16,740)
HECO Consolidated
Operating revenues		728,793	787,685	1,444,990	1,535,623
Operating expenses
Fuel oil		289,278	331,064	594,378	658,903
Purchased power		178,444	188,352	331,808	353,141
Other operation		66,184	64,516	137,607	126,365
Maintenance		27,340	31,235	57,042	61,273
Depreciation		38,590	36,133	76,870	72,615
Taxes, other than income taxes		68,759	76,304	136,446	147,299
Income taxes		18,333	18,574	32,428	35,939
Total operating expenses		686,928	746,178	1,366,579	1,455,535
Operating income		41,865	41,507	78,411	80,088
Other income (loss)
Allowance for equity funds used during construction		1,560	1,997	2,775	3,937
Other, net		940	1,414	3,252	2,723
Income tax benefits (expense)		8	(51)	(291)	(95)
Total other income		2,508	3,360	5,736	6,565
Interest and other charges
Interest on long-term debt		14,614	15,323	29,228	29,706
Amortization of net bond premium and expense		647	661	1,294	1,406
Other interest charges (credits)		318	(99)	633	(370)
Allowance for borrowed funds used during construction		(398)	(893)	(1,128)	(1,763)
Total interest and other charges		15,181	14,992	30,027	28,979
Net income		29,192	29,875	54,120	57,674
Preferred stock dividends of subsidiaries		229	229	458	458
Net income attributable to HECO		28,963	29,646	53,662	57,216
Preferred stock dividends of HECO		270	270	540	540
Net income for common stock		$ 28,693	$ 29,376	$ 53,122	$ 56,676