Consolidating financial information (Details 5) - HECO (USD $) In Thousands, unless otherwise specified	3 Months Ended											3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 HECO	Mar. 31, 2012 HECO	Mar. 31, 2013 HELCO	Mar. 31, 2012 HELCO	Mar. 31, 2013 MECO	Mar. 31, 2012 MECO	Mar. 31, 2012 Other subsidiaries	Mar. 31, 2013 Other subsidiaries	Dec. 31, 2012 Other subsidiaries	Mar. 31, 2013 Consolidating adjustments	Mar. 31, 2012 Consolidating adjustments	Mar. 31, 2013 HECO Consolidated	Mar. 31, 2012 HECO Consolidated
Cash flows from operating activities
Net income (loss)	$ 34,152	$ 38,789	$ 24,699	$ 27,570	$ 4,554	$ 6,745	$ 6,660	$ 1,975	$ (1)			$ (10,985)	$ (8,490)	$ 24,928	$ 27,799
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings			(11,010)	(8,515)								10,985	8,490	(25)	(25)
Common stock dividends received from subsidiaries			7,052	5,471								(7,052)	(5,471)
Depreciation of property, plant and equipment	39,726	37,911	24,707	22,571	8,547	8,436	5,026	5,475						38,280	36,482
Other amortization	935	1,419	(8)	485	358	622	607	454						957	1,561
Change in deferred income taxes	19,967	21,260	13,572	13,721	2,755	2,563	1,648	3,777						17,975	20,061
Changes in tax credits, net			1,299	1,320	(17)	36	100							1,382	1,356
Allowance for equity funds used during construction	(1,215)	(1,940)	(983)	(1,581)	(138)	(125)	(94)	(234)						(1,215)	(1,940)
Changes in assets and liabilities
Decrease (increase) in accounts receivable			34,652	19,978	(13)	343	3,495	2,431				569	2,249	38,703	25,001
Decrease (Increase) in accrued unbilled revenues			(1,707)	11,188	(2,091)	57	2,481	(61)						(1,317)	11,184
Decrease (increase) in fuel oil stock	(29,272)	(14,458)	(30,155)	(11,819)	2,056	(2,058)	(1,173)	(581)						(29,272)	(14,458)
Increase in materials and supplies			(1,853)	(2,320)	(614)	(1,128)	(878)	(113)						(3,345)	(3,561)
Increase in regulatory assets	(17,746)	(13,948)	(13,071)	(11,612)	(2,464)	(1,039)	(2,211)	(1,297)						(17,746)	(13,948)
Increase (decrease) in accounts payable			44,887	(27,400)	(903)	(2,941)	(5,050)	(2,833)						38,934	(33,174)
Changes in prepaid and accrued income taxes and revenue taxes	(50,933)	(41,126)	(41,093)	(29,011)	(8,078)	(5,741)	(4,495)	(9,809)						(53,666)	(44,561)
Contributions to defined benefit pension and other postretirement benefit plans	(21,476)	(26,815)	(15,530)	(19,428)	(2,763)	(3,279)	(2,717)	(3,476)						(21,010)	(26,183)
Change in other assets and liabilities			11,117	(2,190)	5,170	2,320	4,220	5,589	(1)			(569)	(2,249)	19,938	3,469
Net cash provided by (used in) operating activities	48,319	(15,716)	46,575	(11,572)	6,359	4,811	7,619	1,297	(2)			(7,052)	(5,471)	53,501	(10,937)
Cash flows from investing activities
Capital expenditures	(71,041)	(65,300)	(47,709)	(51,026)	(10,118)	(6,727)	(10,088)	(5,683)						(67,915)	(63,436)
Contributions in aid of construction	11,710	22,855	7,816	20,748	3,432	1,579	462	528						11,710	22,855
Advances from (to) affiliates			(3,600)		1,400	10,250		14,500				2,200	(24,750)
Net cash used in investing activities	(112,551)	(80,862)	(43,493)	(30,278)	(5,286)	5,102	(9,626)	9,345				2,200	(24,750)	(56,205)	(40,581)
Cash flows from financing activities
Common stock dividends	(24,394)	(23,855)	(20,070)	(18,261)	(3,610)	(3,284)	(3,442)	(2,187)				7,052	5,471	(20,070)	(18,261)
Preferred stock dividends of HECO and subsidiaries			(270)	(270)	(134)	(134)	(95)	(95)						(499)	(499)
Repayment of long-term debt	(50,000)	(57,500)		(42,580)		(7,200)		(7,720)							(57,500)
Net increase in short-term borrowings from nonaffiliates and affiliate with original maturities of three months or less	50,244	87,467	41,652	60,192			3,600					(2,200)	24,750	43,052	84,942
Other	(3,240)	(3,757)	2	(70)		(2)		(48)						2	(120)
Net cash provided by financing activities	107,278	62,659	21,314	(989)	(3,744)	(10,620)	63	(10,050)				4,852	30,221	22,485	8,562
Net increase (decrease) in cash and cash equivalents	43,046	(33,919)	24,396	(42,839)	(2,671)	(707)	(1,944)	592	(2)					19,781	(42,956)
Cash and cash equivalents, beginning of period			8,265	44,819	5,441	3,383	3,349	496	108	104	104			17,159	48,806
Cash and cash equivalents, end of period			$ 32,661	$ 1,980	$ 2,770	$ 2,676	$ 1,405	$ 1,088	$ 106	$ 104	$ 104			$ 36,940	$ 5,850