Subsequent event (Details) - HECO (USD $)	3 Months Ended		1 Months Ended					1 Months Ended			1 Months Ended		1 Months Ended		1 Months Ended		1 Months Ended		1 Months Ended			1 Months Ended		1 Months Ended		1 Months Ended			1 Months Ended		3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Apr. 30, 2012 Issuance of notes in private placement D agency	Apr. 30, 2012 Issuance of notes in private placement Special purpose revenue bonds	Apr. 19, 2012 Issuance of notes in private placement Special purpose revenue bonds	Apr. 19, 2012 Issuance of notes in private placement Special purpose revenue bonds Minimum	Apr. 19, 2012 Issuance of notes in private placement Special purpose revenue bonds Maximum	Apr. 30, 2012 Issuance of notes in private placement HECO Unsecured senior notes	Apr. 30, 2012 Issuance of notes in private placement HECO 3.79%, series 2012A, due 2018	Apr. 19, 2012 Issuance of notes in private placement HECO 3.79%, series 2012A, due 2018	Apr. 30, 2012 Issuance of notes in private placement HECO 4.03%, series 2012B, due 2020	Apr. 19, 2012 Issuance of notes in private placement HECO 4.03%, series 2012B, due 2020	Apr. 30, 2012 Issuance of notes in private placement HECO 4.55%, series 2012C, due 2023	Apr. 19, 2012 Issuance of notes in private placement HECO 4.55%, series 2012C, due 2023	Apr. 30, 2012 Issuance of notes in private placement HECO 4.72%, series 2012D, due 2029	Apr. 19, 2012 Issuance of notes in private placement HECO 4.72%, series 2012D, due 2029	Apr. 30, 2012 Issuance of notes in private placement HECO 5.39%, series 2012E, due 2042	Apr. 19, 2012 Issuance of notes in private placement HECO 5.39%, series 2012E, due 2042	Apr. 30, 2012 Issuance of notes in private placement MECO Unsecured senior notes	Apr. 30, 2012 Issuance of notes in private placement MECO 3.79%, series 2012A, due 2018	Apr. 19, 2012 Issuance of notes in private placement MECO 3.79%, series 2012A, due 2018	Apr. 30, 2012 Issuance of notes in private placement MECO 4.03%, series 2012B, due 2020	Apr. 19, 2012 Issuance of notes in private placement MECO 4.03%, series 2012B, due 2020	Apr. 30, 2012 Issuance of notes in private placement MECO 4.55%, series 2012C, due 2023	Apr. 19, 2012 Issuance of notes in private placement MECO 4.55%, series 2012C, due 2023	Apr. 30, 2012 Issuance of notes in private placement HELCO Unsecured senior notes	Apr. 30, 2012 Issuance of notes in private placement HELCO 3.79%, series 2012A, due 2018	Apr. 19, 2012 Issuance of notes in private placement HELCO 3.79%, series 2012A, due 2018	Apr. 30, 2012 Issuance of notes in private placement HELCO 4.55%, series 2012B, due 2023	Apr. 19, 2012 Issuance of notes in private placement HELCO 4.55%, series 2012B, due 2023	Mar. 31, 2012 Repayment of debt HECO Special Purpose Revenue Bonds, 4.95%, refunding series 1998A, due 2012
Subsequent Events
Notes issued through private placement			$ 417,000,000					$ 327,000,000	$ 30,000,000		$ 62,000,000		$ 50,000,000		$ 35,000,000		$ 150,000,000		$ 59,000,000	$ 9,000,000		$ 20,000,000		$ 30,000,000		$ 31,000,000	$ 11,000,000		$ 20,000,000
Interest rate (as a percent)						5.45%	6.20%			3.79%		4.03%		4.55%		4.72%		5.39%			3.79%		4.03%		4.55%			3.79%		4.55%	4.95%
Amount of bonds to be redeemed or refunded				267,000,000
Aggregate principal amount					271,000,000
Percentage of ownership interest by HEI below which holders are required to offer to prepay notes			100.00%
Number of consecutive days during which investment grade rating is to be maintained			90
Number of rating agencies			1
Repayment of long-term debt	$ (57,500,000)	$ (50,000,000)																													$ (57,500,000)