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Income taxes - Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Changes in total unrecognized tax benefits |  |  |
Unrecognized tax benefits, at the beginning of the period | $ 4.0 | $ 3.8 | $ 3.6
Additions based on tax positions taken during the year | 0.3 | 0.9 | 0.0
Reductions based on tax positions taken during the year | 0.0 | (0.2) | (0.1)
Additions for tax positions of prior years | 0.1 | 0.0 | 0.3
Reductions for tax positions of prior years | (0.1) | (0.5) | 0.0
Lapses of statute of limitations | (2.2) | 0.0 | 0.0
Unrecognized tax benefits, at the end of the period | 2.1 | 4.0 | 3.8
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Changes in total unrecognized tax benefits |  |  |
Unrecognized tax benefits, at the beginning of the period | 3.5 | 3.8 | 3.6
Additions based on tax positions taken during the year | 0.3 | 0.4 | 0.0
Reductions based on tax positions taken during the year | 0.0 | (0.2) | (0.1)
Additions for tax positions of prior years | 0.1 | 0.0 | 0.3
Reductions for tax positions of prior years | (0.1) | (0.5) | 0.0
Lapses of statute of limitations | (2.2) | 0.0 | 0.0
Unrecognized tax benefits, at the end of the period | $ 1.6 | $ 3.5 | $ 3.8

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- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 10B -URI http://asc.fasb.org/extlink&oid=84176650&loc=SL37586934-109318 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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