Credit agreement and changes in long-term debt - (Details 2) - HECO (USD $)	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				0 Months Ended
	Apr. 30, 2012 D agency	Apr. 30, 2012 Unsecured senior notes HECO	Apr. 30, 2012 Unsecured senior notes HELCO	Apr. 30, 2012 Unsecured senior notes MECO	Apr. 30, 2012 3.79%, series 2012A, due 2018 HECO	Apr. 19, 2012 3.79%, series 2012A, due 2018 HECO	Apr. 30, 2012 3.79%, series 2012A, due 2018 HELCO	Apr. 19, 2012 3.79%, series 2012A, due 2018 HELCO	Apr. 30, 2012 3.79%, series 2012A, due 2018 MECO	Apr. 19, 2012 3.79%, series 2012A, due 2018 MECO	Apr. 30, 2012 4.03%, series 2012B, due 2020 HECO	Apr. 19, 2012 4.03%, series 2012B, due 2020 HECO	Apr. 30, 2012 4.03%, series 2012B, due 2020 MECO	Apr. 19, 2012 4.03%, series 2012B, due 2020 MECO	Apr. 30, 2012 4.55%, series 2012C, due 2023 HECO	Apr. 19, 2012 4.55%, series 2012C, due 2023 HECO	Apr. 30, 2012 4.55%, series 2012C, due 2023 MECO	Apr. 19, 2012 4.55%, series 2012C, due 2023 MECO	Apr. 30, 2012 4.55%, series 2012B, due 2023 HELCO	Apr. 19, 2012 4.55%, series 2012B, due 2023 HELCO	Apr. 30, 2012 4.72%, series 2012D, due 2029 HECO	Apr. 19, 2012 4.72%, series 2012D, due 2029 HECO	Apr. 30, 2012 5.39%, series 2012E, due 2042 HECO	Apr. 19, 2012 5.39%, series 2012E, due 2042 HECO	Apr. 30, 2012 Special purpose revenue bonds	Apr. 19, 2012 Special purpose revenue bonds	Apr. 19, 2012 Special purpose revenue bonds Minimum	Apr. 19, 2012 Special purpose revenue bonds Maximum	Sep. 13, 2012 4.53%, Series 2012F, due 2032 HECO	Sep. 13, 2012 5.10%, Series 2002A, due 2032 HECO
Long-term debt
Notes issued through private placement	$ 417,000,000	$ 327,000,000	$ 31,000,000	$ 59,000,000	$ 30,000,000		$ 11,000,000		$ 9,000,000		$ 62,000,000		$ 20,000,000		$ 50,000,000		$ 30,000,000		$ 20,000,000		$ 35,000,000		$ 150,000,000						$ 40,000,000	$ 40,000,000
Interest rate (as a percent)						3.79%		3.79%		3.79%		4.03%		4.03%		4.55%		4.55%		4.55%		4.72%		5.39%			5.45%	6.20%	4.53%	5.10%
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