Cover - USD ($)	12 Months Ended
	Dec. 31, 2021	Feb. 23, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	001-37875
Entity Registrant Name	FB FINANCIAL CORPORATION
Entity Incorporation, State or Country Code	TN
Entity Tax Identification Number	62-1216058
Entity Address, Address Line One	211 Commerce Street
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	Nashville
Entity Address, State or Province	TN
Entity Address, Postal Zip Code	37201
City Area Code	615
Local Phone Number	564-1212
Title of 12(b) Security	Common Stock, Par Value $1.00 Per Share
Trading Symbol	FBK
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Reporting Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 1,325,489,775
Entity Common Stock, Shares Outstanding		47,563,875
Current Fiscal Year End Date	--12-31
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity Central Index Key	0001649749