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

Fair Value Measurements - Schedule of Residual Interests Securitized Receivables and Derivatives Carried at Fair Value (Parenthetical) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Allowance for loan losses on financing receivables	$ 1,200,000	$ 11,000,000	$ 0
Amortized costs	26,900,000
Financing Receivable [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net fair value collateral impaired loan	800,000	800,000
Allowance for loan losses on financing receivables	$ 1,200,000	$ 11,000,000