Fair value measurements - (Details) - HECO (USD $)	Sep. 30, 2012	Dec. 31, 2011
Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Undiscounted future cash outflows used to compute fair value of asset retirement obligations	$ 33,000,000
Carrying or notional amount
Financial assets
Cash and cash equivalents (Level 2)	168,502,000	270,255,000
Financial liabilities
Long-term debt, net, including amounts due within one year (Level 2)	1,429,869,000	1,340,070,000
Carrying or notional amount \| Hawaiian Electric Company, Inc. and Subsidiaries \| Fair value measurements on a recurring basis
Financial assets
Cash and cash equivalents (Level 2)	15,722,000	48,806,000
Financial liabilities
Short-term borrowings - nonaffiliates (Level 2)	44,719,000
Long-term debt, net, including amounts due within one year (Level 2)	1,147,869,000	1,058,070,000
Estimated fair value
Financial assets
Cash and cash equivalents (Level 2)	168,502,000	270,255,000
Financial liabilities
Long-term debt, net, including amounts due within one year (Level 2)	1,491,860,000	1,400,241,000
Estimated fair value \| Level 2
Financial assets
Cash and cash equivalents (Level 2)	168,502,000
Financial liabilities
Long-term debt, net, including amounts due within one year (Level 2)	1,491,860,000
Estimated fair value \| Hawaiian Electric Company, Inc. and Subsidiaries \| Fair value measurements on a recurring basis
Financial assets
Cash and cash equivalents (Level 2)	15,722,000	48,806,000
Financial liabilities
Short-term borrowings - nonaffiliates (Level 2)	44,719,000
Long-term debt, net, including amounts due within one year (Level 2)	$ 1,178,889,000	$ 1,095,133,000

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

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