Electric utility subsidiary (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Expenses
Purchased power									$ 690,000
Operating income from regulated and nonregulated activities before income taxes (per HEI consolidated statements of income)	68,170	94,490	63,661	63,375	59,242	72,631	63,631	60,707	289,696	256,211	187,664
Allowance for equity funds used during construction									5,964	6,016	12,222
Allowance for borrowed funds used during construction									2,498	2,558	5,268
Income before income taxes									216,052	183,247	128,824
Income taxes									75,932	67,822	43,923
Net income									140,120	115,425	84,901
Preferred stock dividends of subsidiaries									1,890	1,890	1,890
Net income for common stock	34,225	48,404	27,139	28,462	24,698	32,449	29,262	27,126	138,230	113,535	83,011
Electric utility
Revenues
Operating revenues									2,973,764	2,367,441	2,026,672
Other - nonregulated									4,926	14,925	8,337
Total revenues									2,978,690	2,382,366	2,035,009
Expenses
Fuel oil									1,265,126	900,408	671,970
Purchased power									689,652	548,800	499,804
Other operation									257,065	251,027	248,515
Maintenance									121,219	127,487	107,531
Depreciation									142,975	149,708	144,533
Taxes, other than income taxes									276,504	222,117	191,699
Other - nonregulated									11,015	4,431	1,286
Total expenses									2,763,556	2,203,978	1,865,338
Operating income from regulated and nonregulated activities before income taxes (per HEI consolidated statements of income)									215,134	178,388	169,671
Allowance for equity funds used during construction									5,964	6,016	12,222
Interest expense and other charges									(60,031)	(61,510)	(57,944)
Allowance for borrowed funds used during construction									2,498	2,558	5,268
Income before income taxes									163,565	125,452	129,217
Income taxes									61,584	46,868	47,776
Net income									101,981	78,584	81,441
Preferred stock dividends of subsidiaries									915	915	915
Net income attributable to HECO									101,066	77,669	80,526
Preferred stock dividends of HECO									1,080	1,080	1,080
Net income for common stock									$ 99,986	$ 76,589	$ 79,446