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Bank segment (HEI only) - Additional Information (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 1988
Maximum |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Prepaid assessment rate for financial institutions, lowest risk category | 0.09% |  |  |
Prepaid assessment rate for financial institutions, highest risk category | 0.45% |  |  |
Minimum |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Prepaid assessment rate for financial institutions, lowest risk category | 0.025% |  |  |
Prepaid assessment rate for financial institutions, highest risk category | 0.30% |  |  |
American Savings Bank (ASB) |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Borrowing capacity | $ 1,800.0 | $ 1,800.0 |  |
Cash dividends paid | 37.5 | 36.0 |  |
Hawaiian Electric Industries, Inc. |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Cash dividends paid | 125.0 | 130.0 | $ 121.0 |
Hawaiian Electric Industries, Inc. | Consolidated subsidiary | American Savings Bank (ASB) | Management and administrative services |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Revenue from related party | 2.1 | $ 2.3 | $ 2.1 |
Hawaiian Electric Industries, Inc. | Maximum |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Obligation to contribute additional capital under the Capital Maintenance Agreement |  |  |  | $ 65.1
Reduction in obligation to contribute additional capital under the Capital Maintenance Agreement | $ 28.3 |  |  |

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- Definition This element represents disclosure of the total aggregate cash dividends paid to the entity by consolidated subsidiaries, by unconsolidated subsidiaries, and by 50% or less owned persons accounted for using the equity method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(b)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 235 -Section S99 -Paragraph 2 -Subparagraph (SX 210.9-06) -URI http://asc.fasb.org/extlink&oid=6882215&loc=d3e537971-122884 + Details
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- Definition Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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