| Form N-CSR Cover | 6 Months Ended |
| May 31, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Fidelity Phillips Street Trust |
| Entity Central Index Key | 0000278001 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | May 31, 2024 |
| Shareholder Report | 6 Months Ended |
| May 31, 2024 USD ($) shares | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Fidelity Phillips Street Trust |
| Entity Central Index Key | 0000278001 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | May 31, 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 semi-annual shareholder report contains information about Fidelity® Government Cash Reserves for the period December 1, 2023 to May 31, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-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. |
| 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 six months? (based on hypothetical $10,000 investment) Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment Fidelity® Government Cash Reserves $ 0.40 % |
| Expenses Paid, Amount | $ 20 |
| Expense Ratio, Percent | 0.40% |
| Net Assets | $ 218,855,553,492 |
| Holdings Count | shares | 464 |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of May 31, 2024) KEY FACTS Fund Size $ Number of Holdings 464 |
| Holdings [Text Block] | EFFECTIVE MATURITY DIVERSIFICATION (% of Fund's net assets) Days 1-7 63.1 8-30 7.5 31-60 13.2 61-90 6.3 91-180 8.1 >180 3.6 Repurchase Agreements 44.6 U.S. Treasury Obligations 31.6 U.S. Government Agency - Debt 25.6 ASSET ALLOCATION (% of Fund's net assets) Net Other Assets (Liabilities) - (1.8)% |
| Shareholder Report, Holdings (Details) - Fidelity Government Cash Reserves | May 31, 2024 |
| EMD0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 63.10% |
| EMD1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.50% |
| EMD2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.20% |
| EMD3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.30% |
| EMD4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.10% |
| EMD5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.60% |
| AARepurchaseAgreementsMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 44.60% |
| AAUSTreasuryObligationsMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 31.60% |
| AAUSGovernmentAgencyDebtMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 25.60% |
