HA Sustainable Infrastructure Capital, Inc. Quarterly report pursuant to Section 13 or 15(d)

Our Portfolio - Schedule of Equity Method Investments (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Jun. 30, 2017	Feb. 28, 2017	Oct. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Projects investment amount	$ 540
Vento I, LLC [Member] \| EDP Renewables [Member] \| Renewable Energy Projects [Member]
Schedule of Equity Method Investments [Line Items]
Projects investment amount	121
Strong Upwind Holdings IV, LLC [Member] \| JP Morgan [Member] \| Renewable Energy Projects [Member]
Schedule of Equity Method Investments [Line Items]
Projects investment amount			$ 56
Northern Frontier LLC [Member] \| Various [Member] \| Renewable Energy Projects [Member]
Schedule of Equity Method Investments [Line Items]
Projects investment amount		$ 87
Buckeye Wind Energy Class B Holdings LLC [Member] \| Invenergy [Member] \| Renewable Energy Projects [Member]
Schedule of Equity Method Investments [Line Items]
Projects investment amount						$ 67
MM Solar Holdings LLC [Member] \| AES [Member] \| Renewable Energy Projects [Member]
Schedule of Equity Method Investments [Line Items]
Projects investment amount					$ 29
Invenergy Gunsight Mountain Holdings LLC [Member] \| Invenergy [Member] \| Renewable Energy Projects [Member]
Schedule of Equity Method Investments [Line Items]
Projects investment amount				$ 36
Other Transactions [Member] \| Various [Member] \| Renewable Energy Projects [Member]
Schedule of Equity Method Investments [Line Items]
Projects investment amount	$ 144