Form N-1A Cover	Sep. 30, 2024
Prospectus [Line Items]
Document Type	497
Amendment Flag	false
Document Creation Date	Dec. 02, 2025
Document Effective Date	Dec. 02, 2025
Registrant Name	First Trust Exchange-Traded Fund II
Entity Central Index Key	0001364608
Entity Investment Company Type	N-1A
Document Period End Date	Sep. 30, 2024
First Trust Nasdaq Cybersecurity ETF
Prospectus [Line Items]
Supplement to Prospectus [Text Block]	Notwithstanding anything to the contrary set forth in the Fund’s summary prospectus and prospectus, the seventh sentence of the third paragraph set forth in the section entitled “Principal Investment Strategies” is hereby deleted in its entirety and replaced with the following: No security may be weighted less than 0.10%.

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The date the document was made available and submitted, in YYYY-MM-DD format. The date of submission, date of acceptance by the recipient, and the document effective date are all potentially different.

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The date when a document, upon receipt and acceptance, becomes officially effective, in YYYY-MM-DD format. Usually it is a system-assigned date time value, but it may be declared by the submitter in some cases.

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For the EDGAR submission types of Form 8-K: the date of the report, the date of the earliest event reported; for the EDGAR submission types of Form N-1A: the filing date; for all other submission types: the end of the reporting or transition period. The format of the date is YYYY-MM-DD.

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The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'.

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A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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One of: N-1A (Mutual Fund), N-1 (Open-End Separate Account with No Variable Annuities), N-2 (Closed-End Investment Company), N-3 (Separate Account Registered as Open-End Management Investment Company), N-4 (Variable Annuity UIT Separate Account), N-5 (Small Business Investment Company), N-6 (Variable Life UIT Separate Account), S-1 or S-3 (Face Amount Certificate Company), S-6 (UIT, Non-Insurance Product).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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