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Label Element Value
Prospectus [Line Items] rr_ProspectusLineItems  
Document Type dei_DocumentType 497
Document Period End Date dei_DocumentPeriodEndDate Aug. 31, 2023
Entity Registrant Name dei_EntityRegistrantName First Trust Exchange-Traded Fund VIII
Entity Central Index Key dei_EntityCentralIndexKey 0001667919
Entity Inv Company Type dei_EntityInvCompanyType N-1A
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Mar. 15, 2024
Document Effective Date dei_DocumentEffectiveDate Mar. 15, 2024
FT Vest International Equity Buffer ETF - March  
Prospectus [Line Items] rr_ProspectusLineItems  
Supplement to Prospectus [Text Block] rr_SupplementToProspectusTextBlock

 

Notwithstanding anything to the contrary in the Fund’s Prospectus or Summary Prospectus, the Average Annual Total Return table in the section entitled “Annual Total Return” is deleted in its entirety and replaced with the following:

Average Annual Total Returns for the Periods Ended December 31, 2023

  1 Year Since
Inception		 Inception
Date
Return Before Taxes 16.08% 3.59% 3/19/2021
Return After Taxes on Distributions 16.08% 3.59%  
Return After Taxes on Distributions and Sale of Fund Shares 9.52% 2.76%  
MSCI EAFE Index (reflects no deduction for fees, expenses or taxes) 18.24% 2.78%