| Document and Entity Information | Mar. 20, 2024 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001865174 |
| Document Type | 8-K |
| Document Period End Date | Mar. 20, 2024 |
| Entity Registrant Name | Goldman Sachs Middle Market Lending Corp. II |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 814-01461 |
| Entity Tax Identification Number | 87-3643363 |
| Entity Address, Address Line One | 200 West Street |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10282 |
| City Area Code | (312) |
| Local Phone Number | 655-4419 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | true |
