Cover - shares	9 Months Ended
	Sep. 30, 2024	Oct. 31, 2024
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2024
Document Transition Report	false
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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Central Index Key	0000798941
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3
Amendment Flag	false
Class A Common Stock, Par Value $1
Document Information [Line Items]
Title of 12(b) Security	Class A Common Stock, Par Value $1
Trading Symbol	FCNCA
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		12,984,310
Depositary Shares, Each Representing a 1/40th Interest in a Share of 5.375% Non-Cumulative Perpetual Preferred Stock, Series A
Document Information [Line Items]
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
5.625% Non-Cumulative Perpetual Preferred Stock, Series C
Document Information [Line Items]
Title of 12(b) Security	5.625% Non-Cumulative Perpetual Preferred Stock, Series C
Trading Symbol	FCNCO
Security Exchange Name	NASDAQ
Class B Common Stock, Par Value $1
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		1,005,185