Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 22, 2021	Jun. 30, 2020
Entity Central Index Key	0000798941
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2020
Entity File Number	001-16715
Entity Registrant Name	FIRST CITIZENS BANCSHARES INC /DE/
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	56-1528994
Entity Address, Address Line One	4300 Six Forks Road
Entity Address, City or Town	Raleigh
Entity Address, State or Province	NC
Entity Address, Postal Zip Code	27609
City Area Code	(919)
Local Phone Number	716-7000
Title of 12(g) Security	Class B Common Stock, Par Value $1
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 2,346,993,887
Class A Common Stock
Title of 12(b) Security	Class A Common Stock, Par Value $1
Trading Symbol	FCNCA
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		8,811,220
Class B Common Stock
Entity Common Stock, Shares Outstanding		1,005,185
Preferred Stock
Title of 12(b) Security	Depositary Shares, Each Representing a 1/40th Interest in a Share of 5.375% Non-Cumulative Perpetual Preferred Stock, Series A
Trading Symbol	FCNCP
Security Exchange Name	NASDAQ