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

Our Portfolio - Our Portfolio - Financing Receivables, Investments, Real Estate and Equity Method Investments - Analysis of Portfolio by Type of Obligor and Credit Quality (Parenthetical) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014 Transactions	Dec. 31, 2013	Sep. 30, 2012
Financing Receivable, Recorded Investment [Line Items]
Allowance for credit losses	$ 1,200,000	$ 11,000,000	$ 0
Number of transactions	75hasi_NumberOfTransactions
Financial receivable outstanding, Average Remaining Balance	11,000,000
Total aggregate remaining balance	21,000,000
U.S. Federal Government [Member]
Financing Receivable, Recorded Investment [Line Items]
Total financing receivable	263,000,000
State, Local, Institutions [Member]
Financing Receivable, Recorded Investment [Line Items]
Total financing receivable	83,000,000
Investment Grade By Independent Rating Agency [Member]
Financing Receivable, Recorded Investment [Line Items]
Total financing receivable	56,000,000
Maximum [Member]
Financing Receivable, Recorded Investment [Line Items]
Financial receivable outstanding, Average Remaining Balance	$ 1,000,000