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

Long-term Debt - Schedule of Interest Rate Swaps which are Designated as Cash Flow Hedges (Detail)

Long-term Debt - Schedule of Interest Rate Swaps which are Designated as Cash Flow Hedges (Detail) - Cash Flow Hedging [Member] - Interest Rate Swap [Member] - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Notional Value	$ 438,000,000	$ 431,000,000
Fair Value	$ (100,000)	1,000,000
HASI SYB Loan Agreement 2015-1 [Member]
Derivatives, Fair Value [Line Items]
Hedged Rate	1.55%
Notional Value		$ 67,000,000
HASI SYB Loan Agreement 2015-1 [Member] \| Minimum [Member]
Derivatives, Fair Value [Line Items]
Maturity		2015-12
HASI SYB Loan Agreement 2015-1 [Member] \| Maximum [Member]
Derivatives, Fair Value [Line Items]
Maturity	2021-09
HASI SYB Loan Agreement 2015-1 [Member] \| Base Rate [Member]
Derivatives, Fair Value [Line Items]
Base Rate	3 month Libor
HASI SYB Loan Agreement 2015-2 A [Member]
Derivatives, Fair Value [Line Items]
Hedged Rate	1.52%
Notional Value	$ 31,000,000	$ 37,000,000
Fair Value	$ 100,000
HASI SYB Loan Agreement 2015-2 A [Member] \| Minimum [Member]
Derivatives, Fair Value [Line Items]
Maturity		2015-12
HASI SYB Loan Agreement 2015-2 A [Member] \| Maximum [Member]
Derivatives, Fair Value [Line Items]
Maturity	2018-12
HASI SYB Loan Agreement 2015-2 A [Member] \| Base Rate [Member]
Derivatives, Fair Value [Line Items]
Base Rate	3 month Libor
HASI SYB Loan Agreement 2015-2 B [Member]
Derivatives, Fair Value [Line Items]
Hedged Rate	2.55%
Notional Value	$ 29,000,000	$ 29,000,000
Fair Value	$ (200,000)	$ (200,000)
HASI SYB Loan Agreement 2015-2 B [Member] \| Minimum [Member]
Derivatives, Fair Value [Line Items]
Maturity		2018-12
HASI SYB Loan Agreement 2015-2 B [Member] \| Maximum [Member]
Derivatives, Fair Value [Line Items]
Maturity	2024-12
HASI SYB Loan Agreement 2015-2 B [Member] \| Base Rate [Member]
Derivatives, Fair Value [Line Items]
Base Rate	3 month Libor
HASI SYB Loan Agreement 2015-3 [Member]
Derivatives, Fair Value [Line Items]
Hedged Rate	2.34%
Notional Value	$ 119,000,000	$ 119,000,000
Fair Value		$ 1,000,000
HASI SYB Loan Agreement 2015-3 [Member] \| Minimum [Member]
Derivatives, Fair Value [Line Items]
Maturity		2020-11
HASI SYB Loan Agreement 2015-3 [Member] \| Maximum [Member]
Derivatives, Fair Value [Line Items]
Maturity	2028-08
HASI SYB Loan Agreement 2015-3 [Member] \| Base Rate [Member]
Derivatives, Fair Value [Line Items]
Base Rate	1 month Libor
HASI SYB Loan Agreement 2016-1 A [Member]
Derivatives, Fair Value [Line Items]
Hedged Rate	1.88%
Notional Value	$ 120,000,000	$ 72,000,000
Fair Value	$ 1,100,000	$ 200,000
HASI SYB Loan Agreement 2016-1 A [Member] \| Minimum [Member]
Derivatives, Fair Value [Line Items]
Maturity		2016-11
HASI SYB Loan Agreement 2016-1 A [Member] \| Maximum [Member]
Derivatives, Fair Value [Line Items]
Maturity	2021-11
HASI SYB Loan Agreement 2016-1 A [Member] \| Base Rate [Member]
Derivatives, Fair Value [Line Items]
Base Rate	3 month Libor
HASI SYB Loan Agreement 2016-1 B [Member]
Derivatives, Fair Value [Line Items]
Hedged Rate	2.73%
Notional Value	$ 107,000,000	$ 107,000,000
Fair Value	$ (1,100,000)
HASI SYB Loan Agreement 2016-1 B [Member] \| Minimum [Member]
Derivatives, Fair Value [Line Items]
Maturity		2021-11
HASI SYB Loan Agreement 2016-1 B [Member] \| Maximum [Member]
Derivatives, Fair Value [Line Items]
Maturity	2032-10
HASI SYB Loan Agreement 2016-1 B [Member] \| Base Rate [Member]
Derivatives, Fair Value [Line Items]
Base Rate	3 month Libor
2017 Master Repurchase Agreement [Member]
Derivatives, Fair Value [Line Items]
Hedged Rate	2.42%
Notional Value	$ 32,000,000
2017 Master Repurchase Agreement [Member] \| Minimum [Member]
Derivatives, Fair Value [Line Items]
Maturity		2019-08
2017 Master Repurchase Agreement [Member] \| Maximum [Member]
Derivatives, Fair Value [Line Items]
Maturity	2033-03
2017 Master Repurchase Agreement [Member] \| Base Rate [Member]
Derivatives, Fair Value [Line Items]
Base Rate	3 month Libor