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Summary of significant accounting policies (Tables) | 12 Months Ended
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Dec. 31, 2017
Accounting Policies [Abstract] |
Schedule of future minimum lease payments | HEI's consolidated and the Utilities' future minimum lease payments are as follows:
(in millions) | HEI |  | Hawaiian Electric
2018 | $ | 11 |  |  | $ | 6 |
2019 | 10 |  |  | 5 |
2020 | 8 |  |  | 5 |
2021 | 7 |  |  | 5 |
2022 | 4 |  |  | 3 |
Thereafter | 36 |  |  | 29 |
| $ | 76 |  |  | $ | 53 |
Summary of amounts in income tax expense related to investments in qualifying affordable housing projects | The table below summarizes the amounts in income tax expense related to ASB's investments in qualifying affordable housing projects:
Years ended December 31 | 2017 |  |  | 2016 |  |  | 2015 |
(in millions) |  |  |  |  |  |  |  |
Amounts in income taxes related to investments in qualifying affordable housing projects |  |  |  |  |  |  |  |
Amortization recognized in the provision for income taxes | $ | (7.4 | ) |  | $ | (5.8 | ) |  | $ | (5.4 | )
Tax credits and other tax benefits recognized in the provision for income taxes | 10.7 |  |  | 8.4 |  |  | 8.0 |
Net benefit to income tax expense | $ | 3.3 |  |  | $ | 2.6 |  |  | $ | 2.6 |

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- Definition Tabular disclosure of future minimum payments required in the aggregate and for each of the five succeeding fiscal years for operating leases having initial or remaining noncancelable lease terms in excess of one year and the total minimum rentals to be received in the future under noncancelable subleases as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717 + Details
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