| Document and Entity Information | Oct. 15, 2020 |
| Document And Entity Information [Line Items] | |
| Entity Registrant Name | CIT GROUP INC |
| Amendment Flag | false |
| Entity Central Index Key | 0001171825 |
| Document Type | 8-K |
| Document Period End Date | Oct. 15, 2020 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-31369 |
| Entity Tax Identification Number | 65-1051192 |
| Entity Address, Address Line One | 11 W. 42nd Street |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10036 |
| City Area Code | (212) |
| Local Phone Number | 461-5200 |
| Written Communications | true |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Common Stock, par value $0.01 per share |
| Trading Symbol | CIT |
| Security Exchange Name | NYSE |
| Series B Preferred Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 5.625% Non-Cumulative Perpetual Preferred Stock, Series B, par value $0.01 per share |
| Trading Symbol | CITPRB |
| Security Exchange Name | NYSE |
