Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 18, 2021
Document Information Line Items
Entity Registrant Name	FAST ACQUISITION CORP.
Trading Symbol	FST
Document Type	10-Q
Current Fiscal Year End Date	--12-31
Amendment Flag	false
Entity Central Index Key	0001815737
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Shell Company	true
Entity Ex Transition Period	false
Document Quarterly Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	DE
Entity File Number	001-39462
Entity Tax Identification Number	85-1338207
Entity Address, Address Line One	109 Old Branchville Rd
Entity Address, City or Town	Ridgefield
Entity Address, State or Province	CT
Entity Address, Postal Zip Code	06877
City Area Code	(917)
Local Phone Number	921-0285
Title of 12(b) Security	Class A common stock, par value $0.0001 per share
Security Exchange Name	NYSE
Entity Interactive Data Current	Yes
Class A Common Stock
Document Information Line Items
Entity Common Stock, Shares Outstanding		20,000,000
Class B Common Stock
Document Information Line Items
Entity Common Stock, Shares Outstanding		5,000,000