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

Our Portfolio - Schedule of Equity Method Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Oct. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Projects investment amount	$ 523
Northern Frontier LLC [Member] \| NextEra Energy [Member] \| Renewable Energy Projects [Member]
Schedule of Equity Method Investments [Line Items]
Projects investment amount	127
Vento I, LLC [Member] \| EDP Renewables [Member] \| Renewable Energy Projects [Member]
Schedule of Equity Method Investments [Line Items]
Projects investment amount	119
Buckeye Wind Energy Class B Holdings LLC [Member] \| Invenergy [Member] \| Renewable Energy Projects [Member]
Schedule of Equity Method Investments [Line Items]
Projects investment amount				$ 68
Invenergy Gunsight Mountain Holdings LLC [Member] \| Invenergy [Member] \| Renewable Energy Projects [Member]
Schedule of Equity Method Investments [Line Items]
Projects investment amount		$ 37
MM Solar Parent LLC [Member] \| AES [Member] \| Renewable Energy Projects [Member]
Schedule of Equity Method Investments [Line Items]
Projects investment amount			$ 29
Helix Fund Vento I, LLC [Member] \| Various [Member] \| Renewable Energy Projects [Member]
Schedule of Equity Method Investments [Line Items]
Projects investment amount			$ 25
Other Transactions [Member] \| Various [Member] \| Renewable Energy Projects [Member]
Schedule of Equity Method Investments [Line Items]
Projects investment amount	$ 118