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

Securitization of Receivables - Schedule of Cash Flows between us and Securitization Trusts (Detail) (Securitization Trust [Member], USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2012
Securitization Trust [Member]
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Purchase of receivables securitized	$ 57.1	$ 248.7	$ 260.1	$ 142.0
Proceeds from securitizations	59.6	257.2	265.7	146.0
Servicing fees received	0.1	0.6	0.6	0.7
Cash received from residual assets	$ 0.2	$ 0.9	$ 0.5	$ 0.6