Consolidating financial information (Details 5) - 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
Cash flows from operating activities
Net income (loss)	$ 48,177	$ 48,875	$ 126,239	$ 105,422
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation of property, plant and equipment			112,946	111,516
Other amortization			4,811	14,552
Change in deferred income taxes			82,582	60,957
Allowance for equity funds used during construction	(1,611)	(1,570)	(5,548)	(4,131)
Change in cash overdraft				(2,688)
Changes in assets and liabilities
Decrease (increase) in fuel oil stock			(31,372)	(4,592)
Change in prepaid and accrued income taxes and utility revenue taxes			(5,121)	40,418
Contributions to defined benefit pension and other postretirement benefit plans			(64,006)	(56,395)
Net cash provided by operating activities			121,604	101,089
Cash flows from investing activities
Capital expenditures			(225,961)	(148,107)
Contributions in aid of construction			33,106	15,106
Other			865	(2,923)
Net cash used in investing activities			(297,249)	(169,702)
Cash flows from financing activities
Common stock dividends			(71,966)	(77,070)
Proceeds from issuance of long-term debt			457,000	125,000
Repayment of long-term debt			(368,500)	(150,000)
Net increase in short-term borrowings from nonaffiliates and affiliate with original maturities of three months or less			13,398	26,272
Proceeds from issuance of common stock			16,881	14,861
Other			(6,314)	(4,283)
Net cash provided by (used in) financing activities			73,892	21,445
Net increase (decrease) in cash and cash equivalents			(101,753)	(47,168)
HECO
Cash flows from operating activities
Net income (loss)	38,645	38,229	95,861	74,982
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Equity in earnings of subsidiaries			(28,100)	(34,457)
Common stock dividends received from subsidiaries			16,464	21,171
Depreciation of property, plant and equipment			68,046	67,381
Other amortization			691	9,390
Change in deferred income taxes			64,790	33,606
Change in tax credits, net			3,256	771
Allowance for equity funds used during construction	(1,323)	(1,220)	(4,558)	(3,154)
Changes in assets and liabilities
Decrease (increase) in accounts receivable			(43,284)	(33,705)
Decrease (increase) in accrued unbilled revenues			3,427	(32,482)
Decrease (increase) in fuel oil stock			(36,365)	7,631
Increase in materials and supplies			(6,320)	(4,640)
Increase in regulatory assets			(44,175)	(27,602)
Increase (decrease) in accounts payble			7,872	(52,693)
Change in prepaid and accrued income taxes and utility revenue taxes			(14,006)	25,633
Contributions to defined benefit pension and other postretirement benefit plans			(45,878)	(40,944)
Change in other assets and liabilities			5,451	5,582
Net cash provided by operating activities			43,172	16,470
Cash flows from investing activities
Capital expenditures			(172,872)	(100,033)
Contributions in aid of construction			25,547	9,381
Other				77
Investment in consolidated subsidiary				(25)
Net cash used in investing activities			(147,325)	(90,600)
Cash flows from financing activities
Common stock dividends			(54,783)	(52,919)
Preferred stock dividends of HECO and subsidiaries			(810)	(810)
Proceeds from issuance of long-term debt			367,000
Repayment of long-term debt			(259,580)
Net increase in short-term borrowings from nonaffiliates and affiliate with original maturities of three months or less			16,469	15,748
Other			(1,980)	(61)
Net cash provided by (used in) financing activities			66,316	(38,042)
Net increase (decrease) in cash and cash equivalents			(37,837)	(112,172)
Cash and cash equivalents, beginning of period			44,819	121,019
Cash and cash equivalents, end of period	6,982	8,847	6,982	8,847
HELCO
Cash flows from operating activities
Net income (loss)	4,861	8,121	16,230	21,580
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation of property, plant and equipment			25,036	24,619
Other amortization			1,776	1,928
Change in deferred income taxes			8,290	9,801
Change in tax credits, net			256	510
Allowance for equity funds used during construction	(148)	(131)	(433)	(447)
Change in cash overdraft				(2,527)
Changes in assets and liabilities
Decrease (increase) in accounts receivable			(7,236)	(3,600)
Decrease (increase) in accrued unbilled revenues			3,107	(1,719)
Decrease (increase) in fuel oil stock			3,163	(4,691)
Increase in materials and supplies			(719)	(86)
Increase in regulatory assets			(6,621)	(1,551)
Increase (decrease) in accounts payble			(8,518)	100
Change in prepaid and accrued income taxes and utility revenue taxes			(3,562)	8,760
Contributions to defined benefit pension and other postretirement benefit plans			(8,270)	(6,914)
Change in other assets and liabilities			5,013	1,429
Net cash provided by operating activities			27,512	47,192
Cash flows from investing activities
Capital expenditures			(26,331)	(22,770)
Contributions in aid of construction			4,199	3,884
Advances from (to) affiliates			16,750	(13,750)
Net cash used in investing activities			(5,382)	(32,636)
Cash flows from financing activities
Common stock dividends			(9,854)	(12,093)
Preferred stock dividends of HECO and subsidiaries			(400)	(400)
Proceeds from issuance of long-term debt			31,000
Repayment of long-term debt			(41,200)
Other			167
Net cash provided by (used in) financing activities			(20,287)	(12,493)
Net increase (decrease) in cash and cash equivalents			1,843	2,063
Cash and cash equivalents, beginning of period			3,383	1,229
Cash and cash equivalents, end of period	5,226	3,292	5,226	3,292
MECO
Cash flows from operating activities
Net income (loss)	6,653	4,038	12,484	13,496
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation of property, plant and equipment			15,474	15,673
Other amortization			1,607	1,376
Change in deferred income taxes			9,637	7,713
Change in tax credits, net			130	135
Allowance for equity funds used during construction	(140)	(219)	(557)	(530)
Change in cash overdraft				(161)
Changes in assets and liabilities
Decrease (increase) in accounts receivable			1,287	(5,926)
Decrease (increase) in accrued unbilled revenues			(798)	698
Decrease (increase) in fuel oil stock			1,830	(7,532)
Increase in materials and supplies			(266)	(554)
Increase in regulatory assets			(6,997)	(5,078)
Increase (decrease) in accounts payble			(2,835)	(6,933)
Change in prepaid and accrued income taxes and utility revenue taxes			(3,097)	10,105
Contributions to defined benefit pension and other postretirement benefit plans			(8,269)	(7,377)
Change in other assets and liabilities			6,115	2,807
Net cash provided by operating activities			25,745	17,912
Cash flows from investing activities
Capital expenditures			(21,767)	(19,931)
Contributions in aid of construction			3,360	1,841
Advances from (to) affiliates			11,500	10,500
Net cash used in investing activities			(6,907)	(7,590)
Cash flows from financing activities
Common stock dividends			(6,560)	(9,003)
Preferred stock dividends of HECO and subsidiaries			(286)	(286)
Proceeds from issuance of long-term debt			59,000
Repayment of long-term debt			(67,720)
Other			(359)	(6)
Net cash provided by (used in) financing activities			(15,925)	(9,295)
Net increase (decrease) in cash and cash equivalents			2,913	1,027
Cash and cash equivalents, beginning of period			496	594
Cash and cash equivalents, end of period	3,409	1,621	3,409	1,621
Other subsidiaries
Cash flows from operating activities
Net income (loss)	(1)	(2)	(3)	(8)
Changes in assets and liabilities
Change in other assets and liabilities				(2)
Net cash provided by operating activities			(3)	(10)
Cash flows from financing activities
Proceeds from issuance of common stock				25
Net cash provided by (used in) financing activities				25
Net increase (decrease) in cash and cash equivalents			(3)	15
Cash and cash equivalents, beginning of period			108	94
Cash and cash equivalents, end of period	105	109	105	109
Consolidating adjustments
Cash flows from operating activities
Net income (loss)	(11,285)	(11,929)	(28,025)	(34,382)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Equity in earnings of subsidiaries			28,025	34,382
Common stock dividends received from subsidiaries			(16,414)	(21,096)
Changes in assets and liabilities
Decrease (increase) in accounts receivable			12,326	265
Change in other assets and liabilities			(12,326)	(265)
Net cash provided by operating activities			(16,414)	(21,096)
Cash flows from investing activities
Investment in consolidated subsidiary				25
Advances from (to) affiliates			(28,250)	3,250
Net cash used in investing activities			(28,250)	3,275
Cash flows from financing activities
Common stock dividends			16,414	21,096
Net increase in short-term borrowings from nonaffiliates and affiliate with original maturities of three months or less			28,250	(3,250)
Proceeds from issuance of common stock				(25)
Net cash provided by (used in) financing activities			44,664	17,821
HECO Consolidated
Cash flows from operating activities
Net income (loss)	38,873	38,457	96,547	75,668
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Equity in earnings of subsidiaries			(75)	(75)
Common stock dividends received from subsidiaries			50	75
Depreciation of property, plant and equipment			108,556	107,673
Other amortization			4,074	12,694
Change in deferred income taxes			82,717	51,120
Change in tax credits, net			3,642	1,416
Allowance for equity funds used during construction	(1,611)	(1,570)	(5,548)	(4,131)
Change in cash overdraft				(2,688)
Changes in assets and liabilities
Decrease (increase) in accounts receivable			(36,907)	(42,966)
Decrease (increase) in accrued unbilled revenues			5,736	(33,503)
Decrease (increase) in fuel oil stock			(31,372)	(4,592)
Increase in materials and supplies			(7,305)	(5,280)
Increase in regulatory assets			(57,793)	(34,231)
Increase (decrease) in accounts payble			(3,481)	(59,526)
Change in prepaid and accrued income taxes and utility revenue taxes			(20,665)	44,498
Contributions to defined benefit pension and other postretirement benefit plans			(62,417)	(55,235)
Change in other assets and liabilities			4,253	9,551
Net cash provided by operating activities			80,012	60,468
Cash flows from investing activities
Capital expenditures			(220,970)	(142,734)
Contributions in aid of construction			33,106	15,106
Other				77
Net cash used in investing activities			(187,864)	(127,551)
Cash flows from financing activities
Common stock dividends			(54,783)	(52,919)
Preferred stock dividends of HECO and subsidiaries			(1,496)	(1,496)
Proceeds from issuance of long-term debt			457,000
Repayment of long-term debt			(368,500)
Net increase in short-term borrowings from nonaffiliates and affiliate with original maturities of three months or less			44,719	12,498
Other			(2,172)	(67)
Net cash provided by (used in) financing activities			74,768	(41,984)
Net increase (decrease) in cash and cash equivalents			(33,084)	(109,067)
Cash and cash equivalents, beginning of period			48,806	122,936
Cash and cash equivalents, end of period	$ 15,722	$ 13,869	$ 15,722	$ 13,869