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Significant accounting policies - Estimated And Weighted Average Useful Lives of Depreciable Assets (Detail) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Generation | Minimum |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Estimated useful lives | 3 years | 3 years
Generation | Maximum |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Estimated useful lives | 60 years | 60 years
Generation | Weighted Average |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Estimated useful lives | 33 years | 32 years
Distribution | Minimum |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Estimated useful lives | 5 years | 5 years
Distribution | Maximum |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Estimated useful lives | 100 years | 100 years
Distribution | Weighted Average |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Estimated useful lives | 40 years | 41 years
Equipment and other | Minimum |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Estimated useful lives | 5 years | 5 years
Equipment and other | Maximum |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Estimated useful lives | 50 years | 50 years
Equipment and other | Weighted Average |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Estimated useful lives | 13 years | 11 years

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- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_ElectricGenerationEquipmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RangeAxis=us-gaap_WeightedAverageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=aqunf_ElectricWaterandGasDistributionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_EquipmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |