| Cover | Jun. 28, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jun. 28, 2021 |
| Entity Registrant Name | JEFFERIES GROUP LLC |
| Entity Central Index Key | 0001084580 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-14947 |
| Entity Tax Identification Number | 95-4719745 |
| Entity Address, Address Line One | 520 Madison Avenue |
| Entity Address, State or Province | NY |
| Entity Address, City or Town | New York, |
| Entity Address, Postal Zip Code | 10022 |
| City Area Code | (212) |
| Local Phone Number | 284-2550 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| 4.850% Senior Notes Due 2027 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 4.850% Senior Notes Due 2027 |
| Trading Symbol | JEF /27A |
| Security Exchange Name | NYSE |
| 5.125% Senior Notes Due 2023 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 5.125% Senior Notes Due 2023 |
| Trading Symbol | JEF /23 |
| Security Exchange Name | NYSE |
