| Form N-CSR Cover | 12 Months Ended |
| Nov. 30, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| Amendment Flag | false |
| Registrant Name | Fidelity Phillips Street Trust |
| Entity Central Index Key | 0000278001 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Nov. 30, 2024 |
| Shareholder Report | 12 Months Ended |
| Nov. 30, 2024 USD ($) shares | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| Amendment Flag | false |
| Registrant Name | Fidelity Phillips Street Trust |
| Entity Central Index Key | 0000278001 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Nov. 30, 2024 |
| Fidelity Government Cash Reserves | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Government Cash Reserves |
| Class Name | Fidelity® Government Cash Reserves |
| Trading Symbol | FDRXX |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains information about Fidelity® Government Cash Reserves for the period December 1, 2023 to November 30, 2024. |
| Shareholder Report Annual or Semi-Annual | annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-800-544-8544 or by sending an e-mail to fidfunddocuments@fidelity.com. |
| Material Fund Change Notice [Text Block] | This report describes changes to the Fund that occurred during the reporting period. |
| Additional Information Phone Number | 1-800-544-8544 |
| Additional Information Email | fidfunddocuments@fidelity.com |
| Additional Information Website | fundresearch.fidelity.com/prospectus/sec |
| Expenses [Text Block] | What were your Fund costs for the last year? (based on hypothetical $10,000 investment) FUND COST (PREVIOUS YEAR) Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment Fidelity® Government Cash Reserves $ 0.39 % |
| Expenses Paid, Amount | $ 40 |
| Expense Ratio, Percent | 0.39% |
| Net Assets | $ 235,513,994,497 |
| Holdings Count | shares | 561 |
| Advisory Fees Paid, Amount | $ 764,527,497 |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of November 30, 2024) KEY FACTS Fund Size $ Number of Holdings 561 Total Advisory Fee $ |
| Holdings [Text Block] | EFFECTIVE MATURITY DIVERSIFICATION (% of Fund's net assets) Days 1-7 58.8 8-30 9.9 31-60 11.4 61-90 11.3 91-180 9.2 >180 2.7 Repurchase Agreements 39.0 U.S. Treasury Obligations 35.3 U.S. Government Agency - Debt 29.0 ASSET ALLOCATION (% of Fund's net assets) Net Other Assets (Liabilities) - (3.3)% |
| Material Fund Change [Text Block] | How has the Fund changed? This is a summary of certain changes to the Fund since December 1, 2023. For more complete information, you may review the Fund's next prospectus, which we expect to be available by January 29, 2025 at fundresearch.fidelity.com/prospectus/sec or upon request at 1-800-544-8544 or by sending an e-mail to fidfunddocuments fidelity.com . The fund's transfer agent and pricing & bookkeeping fees were changed to a fixed rate effective December 1, 2023, through February 29, 2024, in anticipation of the transition to a new management fee structure. Effective March 1, 2024, the fund's management contract was amended to incorporate administrative services previously covered under separate services agreements (transfer agent and pricing & bookkeeping). The amended contract incorporates a management fee rate that may vary by class. The Adviser or an affiliate pays certain expenses of managing and operating the fund out of each class's management fee. The fund's principal investment risks were updated in connection with the implementation of recent rule amendments related to money market funds adopted by the SEC. |
| Material Fund Change Expenses [Text Block] | The fund's transfer agent and pricing & bookkeeping fees were changed to a fixed rate effective December 1, 2023, through February 29, 2024, in anticipation of the transition to a new management fee structure. Effective March 1, 2024, the fund's management contract was amended to incorporate administrative services previously covered under separate services agreements (transfer agent and pricing & bookkeeping). The amended contract incorporates a management fee rate that may vary by class. The Adviser or an affiliate pays certain expenses of managing and operating the fund out of each class's management fee. |
| Material Fund Change Risks Change [Text Block] | The fund's principal investment risks were updated in connection with the implementation of recent rule amendments related to money market funds adopted by the SEC. |
| Summary of Change Legend [Text Block] | This is a summary of certain changes to the Fund since December 1, 2023. For more complete information, you may review the Fund's next prospectus, which we expect to be available by January 29, 2025 at fundresearch.fidelity.com/prospectus/sec or upon request at 1-800-544-8544 or by sending an e-mail to fidfunddocuments fidelity.com . |
| Updated Prospectus Phone Number | 1-800-544-8544</span>" id="sjs-B34"><span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;">1-800-544-8544</span> |
| Updated Prospectus Email Address | fidfunddocuments@fidelity.com</span>" id="sjs-B35"><span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;">fidfunddocuments@fidelity.com</span> |
| Updated Prospectus Web Address | fundresearch.fidelity.com/prospectus/sec</span>" id="sjs-B36"><span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:bold;">fundresearch.fidelity.com/prospectus/sec</span> |
| Shareholder Report, Holdings (Details) - Fidelity Government Cash Reserves | Nov. 30, 2024 |
| EMD0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 58.80% |
| EMD1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.90% |
| EMD2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.40% |
| EMD3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.30% |
| EMD4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.20% |
| EMD5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| AARepurchaseAgreementsMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 39% |
| AAUSTreasuryObligationsMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 35.30% |
| AAUSGovernmentAgencyDebtMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 29% |
