Credit agreement and changes in long-term debt - (Details 2) - HECO (USD $)	1 Months Ended
	Apr. 30, 2012	Apr. 19, 2012
Long-term debt
Notes issued through private placement	$ 417,000,000
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
Unsecured senior notes | HECO
Long-term debt
Notes issued through private placement	327,000,000
Unsecured senior notes | HELCO
Long-term debt
Notes issued through private placement	31,000,000
Unsecured senior notes | MECO
Long-term debt
Notes issued through private placement	59,000,000
3.79%, series 2012A, due 2018 | HECO
Long-term debt
Notes issued through private placement	30,000,000
Interest rate (as a percent)		3.79%
3.79%, series 2012A, due 2018 | HELCO
Long-term debt
Notes issued through private placement	11,000,000
Interest rate (as a percent)		3.79%
3.79%, series 2012A, due 2018 | MECO
Long-term debt
Notes issued through private placement	9,000,000
Interest rate (as a percent)		3.79%
4.03%, series 2012B, due 2020 | HECO
Long-term debt
Notes issued through private placement	62,000,000
Interest rate (as a percent)		4.03%
4.03%, series 2012B, due 2020 | MECO
Long-term debt
Notes issued through private placement	20,000,000
Interest rate (as a percent)		4.03%
4.55%, series 2012C, due 2023 | HECO
Long-term debt
Notes issued through private placement	50,000,000
Interest rate (as a percent)		4.55%
4.55%, series 2012C, due 2023 | MECO
Long-term debt
Notes issued through private placement	30,000,000
Interest rate (as a percent)		4.55%
4.55%, series 2012B, due 2023 | HELCO
Long-term debt
Notes issued through private placement	20,000,000
Interest rate (as a percent)		4.55%
4.72%, series 2012D, due 2029 | HECO
Long-term debt
Notes issued through private placement	35,000,000
Interest rate (as a percent)		4.72%
5.39%, series 2012E, due 2042 | HECO
Long-term debt
Notes issued through private placement	150,000,000
Interest rate (as a percent)		5.39%
Special purpose revenue bonds
Long-term debt
Amount of bonds to be redeemed or refunded	267,000,000
Aggregate principal amount		271,000,000
Special purpose revenue bonds | Minimum
Long-term debt
Interest rate (as a percent)		5.45%
Special purpose revenue bonds | Maximum
Long-term debt
Interest rate (as a percent)		6.20%