| Document and Entity Information | Oct. 15, 2019 | Oct. 11, 2019 |
| Entity Information [Line Items] | ||
| Document Type | 8-K | |
| Document Period End Date | Oct. 15, 2019 | |
| 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 | |
| Entity Emerging Growth Company | false | |
| Entity Central Index Key | 0000831001 | |
| Amendment Flag | false | |
| Soliciting Material | false | |
| Pre-commencement Tender Offer | false | |
| Pre-commencement Issuer Tender Offer | false | |
| Written Communications | false | |
| Common Stock, par value $.01 per share | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | Common Stock, par value $.01 per share | |
| Trading Symbol | C | |
| Security Exchange Name | NYSE | |
| Depositary Shares, each representing 1/1,000th interest in a share of 6.875% Fixed/Floating Rate Noncumulative Preferred Stock, Series K | ||
| Entity Information [Line Items] | ||
| 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 | |
| Depositary Shares, each representing 1/1,000th interest in a share of 6.300% Noncumulative Preferred Stock, Series S | ||
| Entity Information [Line Items] | ||
| 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 | |
| 7.625% Trust Preferred Securities of Citigroup Capital III (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | 7.625% TRUPs of Cap III (and registrant’s guaranty) | |
| Trading Symbol | C/36Y | |
| Security Exchange Name | NYSE | |
| 7.875% Fixed Rate / Floating Rate Trust Preferred Securities (TruPS) of Citigroup Capital XIII (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| 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 | |
| 6.829% Fixed Rate / Floating Rate Enhanced Trust Preferred Securities (Enhanced TruPS) of Citigroup Capital XVIII (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| 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 | |
| C-Tracks Exchange-Traded Notes Based on the Performance of the Miller/Howard MLP Fundamental Index Due September 28, 2023 | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | C-Tracks ETN Miller/Howard MLP Fundamental Index Due Sept 2023 | |
| Trading Symbol | MLPC | |
| Security Exchange Name | NYSEArca | |
| C-Tracks Exchange-Traded Notes Miller/Howard Strategic Dividend Reinvestor Due September 16, 2024 | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | C-Tracks ETN Miller/Howard Strategic Dividend Reinvestor Due Sept 2024 | |
| Trading Symbol | DIVC | |
| Security Exchange Name | NYSEArca | |
| C-Tracks Exchange-Traded Notes on the Miller/Howard MLP Fundamental Index, Series B, Due July 13, 2026 of Citigroup Global Markets Holdings Inc. ("CGMHI") (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | C-Tracks ETN Miller/Howard Fund, Ser B, Due July 2026 of CGMHI (and registrant’s guaranty) | |
| Trading Symbol | MLPE | |
| Security Exchange Name | NYSEArca | |
| Exchange-Traded Notes Based on the Performance of the VelocityShares Daily 4X Long USD vs. JPY Index due December 15, 2032 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | ETN VelocityShares Daily 4X Long USD vs JPY Ind due Dec 2032 of CGMHI (and registrant’s guaranty) | |
| Trading Symbol | DJPY | |
| Security Exchange Name | NYSEArca | |
| Exchange-Traded Notes Based on the Performance of the VelocityShares Daily 4X Long USD vs. GBP Index due December 15, 2032 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | ETN VelocityShares Daily 4X Long USD vs GBP Ind due Dec 2032 of CGMHI (and registrant’s guaranty) | |
| Trading Symbol | DGBP | |
| Security Exchange Name | NYSEArca | |
| Exchange-Traded Notes Based on the Performance of the VelocityShares Daily 4X Long USD vs. EUR Index due December 15, 2032 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | ETN VelocityShares Daily 4X Long USD vs EUR Ind due Dec 2032 of CGMHI (and registrant’s guaranty) | |
| Trading Symbol | DEUR | |
| Security Exchange Name | NYSEArca | |
| Exchange-Traded Notes Based on the Performance of the VelocityShares Daily 4X Long USD vs. CHF Index due December 15, 2032 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | ETN VelocityShares Daily 4X Long USD vs CHF Ind due Dec 2032 of CGMHI (and registrant’s guaranty) | |
| Trading Symbol | DCHF | |
| Security Exchange Name | NYSEArca | |
| Exchange-Traded Notes Based on the Performance of the VelocityShares Daily 4X Long USD vs. AUD Index due December 15, 2032 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | ETN VelocityShares Daily 4X Long USD vs AUD Ind due Dec 2032 of CGMHI (and registrant’s guaranty) | |
| Trading Symbol | DAUD | |
| Security Exchange Name | NYSEArca | |
| Exchange-Traded Notes Based on the Performance of the VelocityShares Daily 4X Long JPY vs. USD Index due December 15, 2032 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | ETN VelocityShares Daily 4X Long JPY vs USD Ind due Dec 2032 of CGMHI (and registrant’s guaranty ) | |
| Trading Symbol | UJPY | |
| Security Exchange Name | NYSEArca | |
| Exchange-Traded Notes Based on the Performance of the VelocityShares Daily 4X Long EUR vs. USD Index due December 15, 2032 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | ETN VelocityShares Daily 4X Long EUR vs USD Ind due Dec 2032 of CGMHI (and registrant’s guaranty ) | |
| Trading Symbol | UEUR | |
| Security Exchange Name | NYSEArca | |
| Exchange-Traded Notes Based on the Performance of the VelocityShares Daily 4X Long GBP vs. USD Index due December 15, 2032 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | ETN VelocityShares Daily 4X Long GBP vs USD Ind due Dec 2032 of CGMHI (and registrant’s guaranty ) | |
| Trading Symbol | UGBP | |
| Security Exchange Name | NYSEArca | |
| Exchange-Traded Notes Based on the Performance of the VelocityShares Daily 4X Long CHF vs. USD Index due December 15, 2032 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | ETN VelocityShares Daily 4X Long CHF vs USD Ind due Dec 2032 of CGMHI (and registrant’s guaranty) | |
| Trading Symbol | UCHF | |
| Security Exchange Name | NYSEArca | |
| Exchange-Traded Notes Based on the Performance of the VelocityShares Daily 4X Long AUD vs. USD Index due December 15, 2032 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | ETN VelocityShares Daily 4X Long AUD vs USD Ind due Dec 2032 of CGMHI (and registrant’s guaranty) | |
| Trading Symbol | UAUD | |
| Security Exchange Name | NYSEArca | |
| VelocityShares Long LIBOR ETNs due August 16, 2032 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | VelocityShares Long LIBOR ETNs due Aug 2032 of CGMHI (and registrant’s guaranty) | |
| Trading Symbol | ULBR | |
| Security Exchange Name | NYSEArca | |
| VelocityShares Short LIBOR ETNs due August 16, 2032 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | VelocityShares Short LIBOR ETNs due Aug 2032 of CGMHI (and registrant’s guaranty) | |
| Trading Symbol | DLBR | |
| Security Exchange Name | NYSEArca | |
| VelocityShares 3x Long Crude Oil ETNs linked to the S&P GSCI Crude Oil Index ER due December 15, 2031 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | VelocityShares 3x Long Crude ETNs due Dec 2031 of CGMHI (and registrant’s guaranty ) | |
| Trading Symbol | UWT | |
| Security Exchange Name | NYSEArca | |
| VelocityShares 3x Inverse Crude Oil ETNs linked to the S&P GSCI Crude Oil Index ER due December 15, 2031 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | VelocityShares 3x Inverse Crude due Dec 2031 of CGMHI (and registrant’s guaranty ) | |
| Trading Symbol | DWT | |
| Security Exchange Name | NYSEArca | |
| Medium-Term Senior Notes, Series N, Callable Step-Up Coupon Notes Due March 31, 2036 of CGMHI (and registrant's guaranty with respect thereto) | ||
| Entity Information [Line Items] | ||
| 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 | |
| Medium-Term Senior Notes, Series G, Callable Fixed Rate Notes Due January 13, 2027 | ||
| Entity Information [Line Items] | ||
| Title of 12(b) Security | MTN, Series G, Callable Fixed Rate Notes Due Jan 2027 | |
| Trading Symbol | C27C | |
| Security Exchange Name | NYSE |
