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

Financing Receivables and Investments - Analysis of Financing Receivables and Investments by Type of Obligor and Credit Quality (Parenthetical) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014 Transactions	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Allowance for credit losses	$ 11,000,000	$ 11,000,000
Number of transactions	13
Financial receivable outstanding, Average Remaining Balance	13,800,000
Total aggregate remaining balance	4,600,000
Maximum [Member]
Financing Receivable, Recorded Investment [Line Items]
Financial receivable outstanding, Average Remaining Balance	1,000,000
Berkshire Hathaway Inc [Member]
Financing Receivable, Recorded Investment [Line Items]
Debt security, carrying value	37,000,000
Debt security, maturity	2035
Exelon Corporation [Member]
Financing Receivable, Recorded Investment [Line Items]
Debt security, carrying value	34,400,000
Debt security, maturity	2033
NRG Energy [Member]
Financing Receivable, Recorded Investment [Line Items]
Allowance for credit losses	11,000,000
Senior debt investment	$ 15,100,000