Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2020	Apr. 24, 2020
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Entity Registrant Name	CIT GROUP INC.
Entity Central Index Key	0001171825
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity File Number	001-31369
Entity Tax Identification Number	65-1051192
Entity Address, Address Line One	11 West 42nd Street
Entity Address, City or Town	New York
Entity Address, Postal Zip Code	10036
City Area Code	212
Local Phone Number	461-5200
Entity Address, State or Province	NY
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		98,366,723
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Incorporation, State or Country Code	DE
Entity Interactive Data Current	Yes
Document Quarterly Report	true
Document Transition Report	false
Common Stock
Document Information [Line Items]
Title of 12(b) Security	Common Stock, par value $0.01 per share
Security Exchange Name	NYSE
Trading Symbol	CIT
5.625% Non-Cumulative Perpetual Preferred Stock, Series B
Document Information [Line Items]
Title of 12(b) Security	5.625% Non-Cumulative Perpetual Preferred Stock, Series B, par value $0.01 per share
Security Exchange Name	NYSE
Trading Symbol	CITPRB