Consolidating financial information (Details) - HECO (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Other income
Allowance for equity funds used during construction	$ 1,997	$ 1,317	$ 3,937	$ 2,561
Interest and other charges
Allowance for borrowed funds used during construction	(893)	(553)	(1,763)	(1,073)
Net income	39,273	27,612	78,062	56,547
Preferred stock dividends of subsidiaries	473	473	946	946
Net income for common stock	38,800	27,139	77,116	55,601
HECO
Operating revenues	567,527	510,653	1,098,140	960,477
Operating expenses
Fuel oil	241,393	220,231	476,419	403,497
Purchased power	141,136	131,921	265,916	244,672
Other operation	44,621	48,396	84,569	95,651
Maintenance	20,542	22,077	41,378	43,269
Depreciation	22,737	22,885	45,308	45,768
Taxes, other than income taxes	55,440	47,108	105,993	88,997
Income taxes	13,361	3,640	25,324	8,338
Total operating expenses	539,230	496,258	1,044,907	930,192
Operating income	28,297	14,395	53,233	30,285
Other income
Allowance for equity funds used during construction	1,654	974	3,235	1,934
Equity in earnings of subsidiaries	8,250	10,963	16,740	22,453
Other, net	1,137	626	2,201	1,358
Total other income	11,041	12,563	22,176	25,745
Interest and other charges
Interest on long-term debt	10,190	9,131	19,320	18,261
Amortization of net bond premium and expense	429	503	912	1,016
Other interest charges (credits)	(167)	442	(554)	820
Allowance for borrowed funds used during construction	(760)	(412)	(1,485)	(820)
Total interest and other charges	9,692	9,664	18,193	19,277
Net income	29,646	17,294	57,216	36,753
Net income attributable to HECO	29,646	17,294	57,216	36,753
Preferred stock dividends of HECO	270	270	540	540
Net income for common stock	29,376	17,024	56,676	36,213
HELCO
Operating revenues	111,741	110,595	224,068	210,230
Operating expenses
Fuel oil	30,616	32,123	63,026	58,614
Purchased power	37,395	32,242	71,303	62,264
Other operation	9,948	9,524	18,963	17,792
Maintenance	4,885	4,297	9,134	8,148
Depreciation	8,301	8,148	16,737	16,471
Taxes, other than income taxes	10,423	10,163	20,886	19,336
Income taxes	2,831	4,725	7,054	8,494
Total operating expenses	104,399	101,222	207,103	191,119
Operating income	7,342	9,373	16,965	19,111
Other income
Allowance for equity funds used during construction	160	233	285	316
Other, net	99	214	200	320
Total other income	259	447	485	636
Interest and other charges
Interest on long-term debt	2,913	2,984	5,898	5,969
Amortization of net bond premium and expense	108	137	245	280
Other interest charges (credits)	20	93	53	174
Allowance for borrowed funds used during construction	(64)	(102)	(115)	(135)
Total interest and other charges	2,977	3,112	6,081	6,288
Net income	4,624	6,708	11,369	13,459
Preferred stock dividends of subsidiaries	133	133	267	267
Net income attributable to HECO	4,491	6,575	11,102	13,192
Net income for common stock	4,491	6,575	11,102	13,192
MECO
Operating revenues	108,417	106,404	213,415	201,246
Operating expenses
Fuel oil	59,055	59,787	119,458	110,890
Purchased power	9,821	7,574	15,922	12,759
Other operation	9,947	9,468	22,833	19,476
Maintenance	5,808	4,902	10,761	9,055
Depreciation	5,095	5,225	10,570	10,451
Taxes, other than income taxes	10,441	9,881	20,420	18,814
Income taxes	2,382	2,795	3,561	5,938
Total operating expenses	102,549	99,632	203,525	187,383
Operating income	5,868	6,772	9,890	13,863
Other income
Allowance for equity funds used during construction	183	110	417	311
Other, net	146	62	257	154
Total other income	329	172	674	465
Interest and other charges
Interest on long-term debt	2,220	2,268	4,488	4,536
Amortization of net bond premium and expense	124	126	249	253
Other interest charges (credits)	66	104	159	199
Allowance for borrowed funds used during construction	(69)	(39)	(163)	(118)
Total interest and other charges	2,341	2,459	4,733	4,870
Net income	3,856	4,485	5,831	9,458
Preferred stock dividends of subsidiaries	96	96	191	191
Net income attributable to HECO	3,760	4,389	5,640	9,267
Net income for common stock	3,760	4,389	5,640	9,267
RHI
Other income
Other, net			(1)	(2)
Total other income			(1)	(2)
Interest and other charges
Net income			(1)	(2)
Net income attributable to HECO			(1)	(2)
Net income for common stock			(1)	(2)
UBC
Other income
Other, net	(1)	(1)	(1)	(4)
Total other income	(1)	(1)	(1)	(4)
Interest and other charges
Net income	(1)	(1)	(1)	(4)
Net income attributable to HECO	(1)	(1)	(1)	(4)
Net income for common stock	(1)	(1)	(1)	(4)
Reclassifications and eliminations
Other income
Equity in earnings of subsidiaries	(8,250)	(10,963)	(16,740)	(22,453)
Other, net	(18)	(3)	(28)	(18)
Total other income	(8,268)	(10,966)	(16,768)	(22,471)
Interest and other charges
Other interest charges (credits)	(18)	(3)	(28)	(18)
Total interest and other charges	(18)	(3)	(28)	(18)
Net income	(8,250)	(10,963)	(16,740)	(22,453)
Net income attributable to HECO	(8,250)	(10,963)	(16,740)	(22,453)
Net income for common stock	(8,250)	(10,963)	(16,740)	(22,453)
HECO Consolidated
Operating revenues	787,685	727,652	1,535,623	1,371,953
Operating expenses
Fuel oil	331,064	312,141	658,903	573,001
Purchased power	188,352	171,737	353,141	319,695
Other operation	64,516	67,388	126,365	132,919
Maintenance	31,235	31,276	61,273	60,472
Depreciation	36,133	36,258	72,615	72,690
Taxes, other than income taxes	76,304	67,152	147,299	127,147
Income taxes	18,574	11,160	35,939	22,770
Total operating expenses	746,178	697,112	1,455,535	1,308,694
Operating income	41,507	30,540	80,088	63,259
Other income
Allowance for equity funds used during construction	1,997	1,317	3,937	2,561
Other, net	1,363	898	2,628	1,808
Total other income	3,360	2,215	6,565	4,369
Interest and other charges
Interest on long-term debt	15,323	14,383	29,706	28,766
Amortization of net bond premium and expense	661	766	1,406	1,549
Other interest charges (credits)	(99)	636	(370)	1,175
Allowance for borrowed funds used during construction	(893)	(553)	(1,763)	(1,073)
Total interest and other charges	14,992	15,232	28,979	30,417
Net income	29,875	17,523	57,674	37,211
Preferred stock dividends of subsidiaries	229	229	458	458
Net income attributable to HECO	29,646	17,294	57,216	36,753
Preferred stock dividends of HECO	270	270	540	540
Net income for common stock	$ 29,376	$ 17,024	$ 56,676	$ 36,213