| Document and Entity Information | Jan. 15, 2021 |
| Document Type | 8-K |
| Document Period End Date | Jan. 15, 2021 |
| Entity File Number | 1-9924 |
| Entity Registrant Name | Citigroup Inc |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 52-1568099 |
| Entity Address, Address Line One | 388 Greenwich Street |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10013 |
| City Area Code | 212 |
| Local Phone Number | 559-1000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000831001 |
| Amendment Flag | false |
| Common Stock [Member] | |
| Title of 12(b) Security | Common Stock, par value $.01 per share |
| Trading Symbol | C |
| Security Exchange Name | NYSE |
| Series J Preferred Stock [Member] | |
| Title of 12(b) Security | Dep Shs, represent 1/1,000th interest in a share of 7.125% Fix/Float Rate Noncum Pref Stk, Ser J |
| Trading Symbol | C Pr J |
| Security Exchange Name | NYSE |
| Series K Preferred Stock [Member] | |
| Title of 12(b) Security | Dep Shs, represent 1/1,000th interest in a share of 6.875% Fix/Float Rate Noncum Pref Stk, Ser K |
| Trading Symbol | C Pr K |
| Security Exchange Name | NYSE |
| Series S Preferred Stock [Member] | |
| Title of 12(b) Security | Depositary Shares, represent 1/1,000th interest in a share of 6.300% Noncum Pref Stock, Ser S |
| Trading Symbol | C Pr S |
| Security Exchange Name | NYSE |
| Citigroup Capital III [Member] | |
| Title of 12(b) Security | 7.625% TRUPs of Cap III (and registrant’s guaranty) |
| Trading Symbol | C/36Y |
| Security Exchange Name | NYSE |
| Citigroup Capital XIII [Member] | |
| Title of 12(b) Security | 7.875% FXD / FRN TruPS of Cap XIII (and registrant’s guaranty) |
| Trading Symbol | C N |
| Security Exchange Name | NYSE |
| Citigroup Capital XVIII [Member] | |
| Title of 12(b) Security | 6.829% FXD / FRN Enhanced TruPS of Cap XVIII (and registrant’s guaranty) |
| Trading Symbol | C/67BP |
| Security Exchange Name | NYSE |
| Series N Medium Term Senior Notes [Member] | |
| Title of 12(b) Security | MTN, Series N, Callable Step-Up Coupon Notes Due Mar 2036 of CGMHI (and registrant’s guaranty) |
| Trading Symbol | C/36A |
| Security Exchange Name | NYSE |
| Series G Medium Term Senior Notes [Member] | |
| Title of 12(b) Security | MTN, Series G, Callable Fixed Rate Notes Due Jan 2027 |
| Trading Symbol | C27C |
| Security Exchange Name | NYSE |
| Series N Medium Term Senior Notes Due Dec 2035 [Member] | |
| Title of 12(b) Security | MTN, Series N, Callable Fixed Rate Notes Due Dec 2035 of CGMHI (and registrant's guaranty) |
| Trading Symbol | C/35 |
| Security Exchange Name | NYSE |
