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

Equity - Schedule of Common Stock Public Offerings (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
4/23/2013 Closing Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Public offerings of common stock, Closing Date	Apr. 23, 2013
Public offerings of common stock, Shares Issued	14,200,000
Public offerings of common stock, Price Per Share	$ 12.50
Net proceeds from offering	$ 160
4/29/2014 Closing Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Public offerings of common stock, Closing Date	Apr. 29, 2014
Public offerings of common stock, Shares Issued	5,800,000
Public offerings of common stock, Price Per Share	$ 13.00
Net proceeds from follow-on from public offering	70
10/31/2014 Closing Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Public offerings of common stock, Closing Date	Oct. 31, 2014
Public offerings of common stock, Shares Issued	4,600,000
Public offerings of common stock, Price Per Share	$ 13.60
Net proceeds from follow-on from public offering	59
5/4/2015 Closing Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Public offerings of common stock, Closing Date	May 04, 2015
Public offerings of common stock, Shares Issued	4,600,000
Public offerings of common stock, Price Per Share	$ 18.50
Net proceeds from follow-on from public offering	$ 81