| Document and Entity Information | Jan. 08, 2020 |
| Document And Entity Information [Line Items] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001084580 |
| Document Type | 8-K |
| Document Period End Date | Jan. 8, 2020 |
| Entity Registrant Name | Jefferies Group LLC |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-14947 |
| Entity Tax Identification Number | 95-4719745 |
| Entity Address, Address Line One | 520 Madison Ave. |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| 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 |
| M 4.850 Senior Notes Due 2027 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 4.850% Senior Notes Due 2027 |
| Trading Symbol | JEF /27A |
| Security Exchange Name | NYSE |
| M 5.125 Senior Notes Due 2023 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 5.125% Senior Notes Due 2023 |
| Trading Symbol | JEF /23 |
| Security Exchange Name | NYSE |
