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Notes Payable (Details Narrative) - USD ($)							12 Months Ended
	Aug. 28, 2020	Jun. 24, 2020	Jun. 22, 2020	May 26, 2020	Apr. 23, 2020	Jun. 27, 2018	Dec. 31, 2020	Dec. 31, 2019	Sep. 21, 2020	Aug. 31, 2020	Feb. 29, 2020
Financing fees and expenses							$ 1,292,338	$ 1,393,400
Debt financing fees							$ 51,160
Warrants exercise per share							$ 0.01	$ 0.01	$ 0.79
Warrants exercisable									75,000	247,525	3,200,000
Loan amount							$ 5,000,000
Net proceeds from issuance of common stock							22,811,669	$ 7,844,852
Initial Horizon Credit Agreement Amendment [Member]
Interest expense, debt, total							808,899	1,006,760
Amortization of debt issuance costs							483,439	$ 386,640
Common Stock Outstanding [Member]
Common stock shares issued			2,666,667
Net proceeds from issuance of common stock			$ 9,100,000
Initial Horizon Credit Agreement [Member]
Line of credit facility, maximum borrowing capacity						$ 10,000,000
Proceeds from lines of credit, total						10,000,000
Debt instrument, end term fee						142,605
Financing fees and expenses						175,000
Loan origination fees						100,000
Debt instrument, unamortized discount						$ 782,116
End of term charge percentage						4.00%
Debt financing fees						$ 400,000
Fair value of warrants						507,116
End of term fees						$ 275,000
Initial Horizon Credit Agreement [Member] | Common Stock Outstanding [Member]
Warrants exercise per share						$ 2.63
Warrants exercisable						190,114
Warrants outstanding						95,057
Amendment to Horizon Credit Agreement [Member] | Horizon Technology Finance Corporation [Member]
Repayment of loans	$ 5,000,000
Debt instrument related end term charges	200,000
Debt instrument face amount	$ 5,000,000
Debt instrument, interest rate terms	The obligations bear interest at a rate calculated based an amount by which the one-month LIBOR exceeds 2% plus 7.625%. In no event shall the interest rate be less than 9.625%. Payments pursuant to the Amendment are interest only for the first twelve (12) months after August 1, 2020, followed by a 21-month amortization period of principal and interest through the scheduled maturity date.
Debt instrument, end term fee	$ 275,000
Debt instrument, restrictive covenants	In connection with the Amendment, Celsion agreed to a liquidity covenant which provides that, at all times, Celsion shall maintain unrestricted cash and/or cash equivalents on deposit in accounts over which the applicable Lenders maintain an account control agreement in an amount not less than $2.5 million. In addition, pursuant to the Amendment, Celsion has agreed to provide evidence to Horizon on or before March 31, 2021, that it has received aggregate cash proceeds of not less than $5 million from the sale of equity, debt, its New Jersey net operating losses, or a combination thereof, subsequent to the date of the Amendment.
Debt instrument, unamortized discount	$ 200,000						$ 109,706
Debt financing fees	5,000
Payment of debt extinguishment	5,000,000
New warrants fair value	$ 247,548
Amendment to Horizon Credit Agreement [Member] | Horizon Technology Finance Corporation [Member] | Common Stock Outstanding [Member]
Warrants exercise per share	$ 1.01
Warrants exercisable	247,525
Warrants cancelled	95,057
Amendment to Horizon Credit Agreement [Member] | Horizon Technology Finance Corporation [Member] | One-Month LIBOR Exceeds 2% Plus [Member]
Debt instrument interest rate	9.625%
April PPP Loan [Member] | Silicon Valley Bank [Member]
Proceeds from loan					$ 632,220
Loan repayment date					May 13, 2020
PPP Loans [Member] | Silicon Valley Bank [Member] | Maximum [Member]
Loan amount					$ 2,000,000
May PPP Loan [Member]
Interest accrued on loan		$ 577
May PPP Loan [Member] | Silicon Valley Bank [Member]
Proceeds from loan				$ 692,530
Loan repayment date				Jun. 24, 2020
May PPP Loan [Member] | Silicon Valley Bank [Member] | Promissory Note [Member]
Debt instrument face amount				$ 692,530

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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