Document and Entity Information - USD ($) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Mar. 03, 2026 |
Jun. 30, 2025 |
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| Cover [Abstract] | |||
| Document Type | 10-K | ||
| Amendment Flag | false | ||
| Document Period End Date | Dec. 31, 2025 | ||
| Document Fiscal Year Focus | 2025 | ||
| Document Fiscal Period Focus | FY | ||
| Entity Registrant Name | West Bay BDC LLC | ||
| Entity Central Index Key | 0002020354 | ||
| Entity Current Reporting Status | Yes | ||
| Entity Interactive Data Current | Yes | ||
| Current Fiscal Year End Date | --12-31 | ||
| Entity Well-known Seasoned Issuer | No | ||
| Entity Voluntary Filers | No | ||
| Document Financial Statement Error Correction [Flag] | false | ||
| ICFR Auditor Attestation Flag | false | ||
| Entity Public Float | $ 0 | ||
| Title of 12(g) Security | Limited Liability Company Common Units | ||
| Entity Filer Category | Non-accelerated Filer | ||
| Entity Shell Company | false | ||
| Entity Small Business | false | ||
| Entity Emerging Growth Company | true | ||
| Securities Act File Number | 814-01758 | ||
| Entity Incorporation, State or Country Code | DE | ||
| Entity Tax Identification Number | 99-1657525 | ||
| 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 | ||
| Document Annual Report | true | ||
| Document Transition Report | false | ||
| Entity Ex Transition Period | true | ||
| Entity Common Stock, Shares Outstanding | 11,833,087 | ||
| Auditor Firm ID | 238 | ||
| Auditor Name | PricewaterhouseCoopers LLP | ||
| Auditor Location | Boston, Massachusetts | ||
| Auditor Opinion [Text Block] | We have audited the accompanying statements of financial condition, including the schedules of investments, of West Bay BDC LLC (the “Company”) as of December 31, 2025 and 2024, and the related statements of operations, changes in members’ capital and cash flows for the year ended December 31, 2025 and for the period from May 1, 2024 (inception) to December 31, 2024, including the related notes (collectively referred to as the “financial statements”). In our opinion, the financial statements present fairly, in all material respects, the financial position of the Company as of December 31, 2025 and 2024, and the results of its operations, changes in its members’ capital and its cash flows for the year ended December 31, 2025 and for the period from May 1, 2024 (inception) to December 31, 2024 in conformity with accounting principles generally accepted in the United States of America. |
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