Long-term debt - Notes of the Partnership and Non-Recourse Debt (Details) - Senior unsecured notes, due June 2036 $ in Millions, $ in Millions	Dec. 31, 2019 CAD ($)	Dec. 31, 2019 USD ($)
Long-term debt
Aggregate borrowings outstanding	$ 210.0
APLP Partnership
Long-term debt
Aggregate borrowings outstanding		$ 161.7
Interest rate (as a percent)	5.95%	5.95%

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant