Fair value measurements (Details) - HECO (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Carrying or notional amount
Financial liabilities
Long-term debt, net, including amounts due within one year	$ 1,422,875	$ 1,422,872
Carrying or notional amount | Hawaiian Electric Company, Inc. and Subsidiaries | Fair value measurements on a recurring basis
Financial liabilities
Short-term borrowings - nonaffiliates	43,052
Long-term debt, net, including amounts due within one year	1,147,875	1,147,872
Estimated fair value
Financial liabilities
Long-term debt, net, including amounts due within one year	1,529,541	1,481,004
Estimated fair value | Level 2
Financial liabilities
Long-term debt, net, including amounts due within one year	1,529,541	1,481,004
Estimated fair value | Hawaiian Electric Company, Inc. and Subsidiaries | Level 2 | Fair value measurements on a recurring basis
Financial liabilities
Short-term borrowings - nonaffiliates	43,052
Long-term debt, net, including amounts due within one year	$ 1,230,067	$ 1,181,631