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

Equity - Schedule of Common Stock Public Offerings (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Apr. 23, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Public offerings of common stock, Price Per Share		$ 12.50us-gaap_SaleOfStockPricePerShare
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
Public offerings of common stock, Net Proceeds	$ 160.0
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
Public offerings of common stock, Net Proceeds	70.4
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
Public offerings of common stock, Net Proceeds	$ 58.9