Shareholder Report |
6 Months Ended | |||||||||
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Apr. 30, 2025
USD ($)
shares
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| Shareholder Report [Line Items] | ||||||||||
| Document Type | N-CSRS | |||||||||
| Amendment Flag | false | |||||||||
| Registrant Name | Fidelity Newbury Street Trust | |||||||||
| Entity Central Index Key | 0000704207 | |||||||||
| Entity Investment Company Type | N-1A | |||||||||
| Document Period End Date | Apr. 30, 2025 | |||||||||
| Fidelity Treasury Money Market Fund - Advisor Class C | ||||||||||
| Shareholder Report [Line Items] | ||||||||||
| Fund Name | Fidelity® Treasury Money Market Fund | |||||||||
| Class Name | Fidelity® Treasury Money Market Fund Advisor C Class | |||||||||
| Trading Symbol | FDCXX | |||||||||
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Treasury Money Market Fund for the period November 1, 2024 to April 30, 2025. | |||||||||
| 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 1-877-208-0098 or by sending an e-mail to funddocuments@fmr.com. | |||||||||
| Additional Information Phone Number | 1-877-208-0098 | |||||||||
| Additional Information Email | funddocuments@fmr.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)
|
|||||||||
| Expenses Paid, Amount | $ 72 | |||||||||
| Expense Ratio, Percent | 1.45% | |||||||||
| Net Assets | $ 45,736,063,311 | |||||||||
| Holdings Count | shares | 120 | |||||||||
| Additional Fund Statistics [Text Block] | Key Fund Statistics
(as of April 30, 2025)
|
|||||||||
| Holdings [Text Block] | EFFECTIVE MATURITY DIVERSIFICATION (% of Fund's net assets) Days 1-7 67.6 8-30 17.0 31-60 4.1 61-90 6.3 91-180 2.1 >180 4.3 Repurchase Agreements 50.7 U.S. Treasury Obligations 50.7 ASSET ALLOCATION (% of Fund's net assets) Repurchase Agreements - 50.7 U.S. Treasury Obligations - 50.7 Net Other Assets (Liabilities) - (1.4)% | |||||||||
| Fidelity Treasury Money Market Fund - Daily Money Class | ||||||||||
| Shareholder Report [Line Items] | ||||||||||
| Fund Name | Fidelity® Treasury Money Market Fund | |||||||||
| Class Name | Fidelity® Treasury Money Market Fund Daily Money Class | |||||||||
| Trading Symbol | FDUXX | |||||||||
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Treasury Money Market Fund for the period November 1, 2024 to April 30, 2025. | |||||||||
| 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 1-877-208-0098 or by sending an e-mail to funddocuments@fmr.com. | |||||||||
| Additional Information Phone Number | 1-877-208-0098 | |||||||||
| Additional Information Email | funddocuments@fmr.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)
|
|||||||||
| Expenses Paid, Amount | $ 35 | |||||||||
| Expense Ratio, Percent | 0.70% | |||||||||
| Net Assets | $ 45,736,063,311 | |||||||||
| Holdings Count | shares | 120 | |||||||||
| Additional Fund Statistics [Text Block] | Key Fund Statistics
(as of April 30, 2025)
|
|||||||||
| Holdings [Text Block] | EFFECTIVE MATURITY DIVERSIFICATION (% of Fund's net assets) Days 1-7 67.6 8-30 17.0 31-60 4.1 61-90 6.3 91-180 2.1 >180 4.3 Repurchase Agreements 50.7 U.S. Treasury Obligations 50.7 ASSET ALLOCATION (% of Fund's net assets) Repurchase Agreements - 50.7 U.S. Treasury Obligations - 50.7 Net Other Assets (Liabilities) - (1.4)% | |||||||||
| Fidelity Tax-Exempt Money Market Fund | ||||||||||
| Shareholder Report [Line Items] | ||||||||||
| Fund Name | Fidelity® Tax-Exempt Money Market Fund | |||||||||
| Class Name | Fidelity® Tax-Exempt Money Market Fund | |||||||||
| Trading Symbol | FMOXX | |||||||||
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Tax-Exempt Money Market Fund for the period November 1, 2024 to April 30, 2025. | |||||||||
| 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)
|
|||||||||
| Expenses Paid, Amount | $ 21 | |||||||||
| Expense Ratio, Percent | 0.42% | |||||||||
| Net Assets | $ 4,137,428,142 | |||||||||
| Holdings Count | shares | 645 | |||||||||
| Additional Fund Statistics [Text Block] | Key Fund Statistics
(as of April 30, 2025)
|
|||||||||
| Holdings [Text Block] | EFFECTIVE MATURITY DIVERSIFICATION (% of Fund's net assets) Days 1-7 78.6 8-30 2.0 31-60 6.5 61-90 2.6 91-180 6.1 >180 4.8 Variable Rate Demand Notes (VRDNs) 40.8 Tender Option Bond 27.6 Municipal Securities 13.4 Commercial Paper 7.1 Net Other Assets (Liabilities) 11.1 ASSET ALLOCATION (% of Fund's net assets) Variable Rate Demand Notes (VRDNs) - 40.8 Tender Option Bond - 27.6 Municipal Securities - 13.4 Commercial Paper - 7.1 Net Other Assets (Liabilities) - 11.1 | |||||||||
| Fidelity Treasury Money Market Fund | ||||||||||
| Shareholder Report [Line Items] | ||||||||||
| Fund Name | Fidelity® Treasury Money Market Fund | |||||||||
| Class Name | Fidelity® Treasury Money Market Fund | |||||||||
| Trading Symbol | FZFXX | |||||||||
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Treasury Money Market Fund for the period November 1, 2024 to April 30, 2025. | |||||||||
| 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)
|
|||||||||
| Expenses Paid, Amount | $ 21 | |||||||||
| Expense Ratio, Percent | 0.42% | |||||||||
| Net Assets | $ 45,736,063,311 | |||||||||
| Holdings Count | shares | 120 | |||||||||
| Additional Fund Statistics [Text Block] | Key Fund Statistics
(as of April 30, 2025)
|
|||||||||
| Holdings [Text Block] | EFFECTIVE MATURITY DIVERSIFICATION (% of Fund's net assets) Days 1-7 67.6 8-30 17.0 31-60 4.1 61-90 6.3 91-180 2.1 >180 4.3 Repurchase Agreements 50.7 U.S. Treasury Obligations 50.7 ASSET ALLOCATION (% of Fund's net assets) Repurchase Agreements - 50.7 U.S. Treasury Obligations - 50.7 Net Other Assets (Liabilities) - (1.4)% | |||||||||
| Fidelity Tax-Exempt Money Market Fund - Daily Money Class | ||||||||||
| Shareholder Report [Line Items] | ||||||||||
| Fund Name | Fidelity® Tax-Exempt Money Market Fund | |||||||||
| Class Name | Fidelity® Tax-Exempt Money Market Fund Daily Money Class | |||||||||
| Trading Symbol | FDEXX | |||||||||
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Tax-Exempt Money Market Fund for the period November 1, 2024 to April 30, 2025. | |||||||||
| 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 1-877-208-0098 or by sending an e-mail to funddocuments@fmr.com. | |||||||||
| Additional Information Phone Number | 1-877-208-0098 | |||||||||
| Additional Information Email | funddocuments@fmr.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)
|
|||||||||
| Expenses Paid, Amount | $ 35 | |||||||||
| Expense Ratio, Percent | 0.70% | |||||||||
| Net Assets | $ 4,137,428,142 | |||||||||
| Holdings Count | shares | 645 | |||||||||
| Additional Fund Statistics [Text Block] | Key Fund Statistics
(as of April 30, 2025)
|
|||||||||
| Holdings [Text Block] | EFFECTIVE MATURITY DIVERSIFICATION (% of Fund's net assets) Days 1-7 78.6 8-30 2.0 31-60 6.5 61-90 2.6 91-180 6.1 >180 4.8 Variable Rate Demand Notes (VRDNs) 40.8 Tender Option Bond 27.6 Municipal Securities 13.4 Commercial Paper 7.1 Net Other Assets (Liabilities) 11.1 ASSET ALLOCATION (% of Fund's net assets) Variable Rate Demand Notes (VRDNs) - 40.8 Tender Option Bond - 27.6 Municipal Securities - 13.4 Commercial Paper - 7.1 Net Other Assets (Liabilities) - 11.1 | |||||||||
| Fidelity Tax-Exempt Money Market Fund - Premium Class | ||||||||||
| Shareholder Report [Line Items] | ||||||||||
| Fund Name | Fidelity® Tax-Exempt Money Market Fund | |||||||||
| Class Name | Fidelity® Tax-Exempt Money Market Fund Premium Class | |||||||||
| Trading Symbol | FZEXX | |||||||||
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Tax-Exempt Money Market Fund for the period November 1, 2024 to April 30, 2025. | |||||||||
| 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)
|
|||||||||
| Expenses Paid, Amount | $ 15 | |||||||||
| Expense Ratio, Percent | 0.30% | |||||||||
| Net Assets | $ 4,137,428,142 | |||||||||
| Holdings Count | shares | 645 | |||||||||
| Additional Fund Statistics [Text Block] | Key Fund Statistics
(as of April 30, 2025)
|
|||||||||
| Holdings [Text Block] | EFFECTIVE MATURITY DIVERSIFICATION (% of Fund's net assets) Days 1-7 78.6 8-30 2.0 31-60 6.5 61-90 2.6 91-180 6.1 >180 4.8 Variable Rate Demand Notes (VRDNs) 40.8 Tender Option Bond 27.6 Municipal Securities 13.4 Commercial Paper 7.1 Net Other Assets (Liabilities) 11.1 ASSET ALLOCATION (% of Fund's net assets) Variable Rate Demand Notes (VRDNs) - 40.8 Tender Option Bond - 27.6 Municipal Securities - 13.4 Commercial Paper - 7.1 Net Other Assets (Liabilities) - 11.1 | |||||||||
| Fidelity Treasury Money Market Fund - Capital Reserves Class | ||||||||||
| Shareholder Report [Line Items] | ||||||||||
| Fund Name | Fidelity® Treasury Money Market Fund | |||||||||
| Class Name | Fidelity® Treasury Money Market Fund Capital Reserves Class | |||||||||
| Trading Symbol | FSRXX | |||||||||
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Treasury Money Market Fund for the period November 1, 2024 to April 30, 2025. | |||||||||
| 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 1-877-208-0098 or by sending an e-mail to funddocuments@fmr.com. | |||||||||
| Additional Information Phone Number | 1-877-208-0098 | |||||||||
| Additional Information Email | funddocuments@fmr.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)
|
|||||||||
| Expenses Paid, Amount | $ 48 | |||||||||
| Expense Ratio, Percent | 0.95% | |||||||||
| Net Assets | $ 45,736,063,311 | |||||||||
| Holdings Count | shares | 120 | |||||||||
| Additional Fund Statistics [Text Block] | Key Fund Statistics
(as of April 30, 2025)
|
|||||||||
| Holdings [Text Block] | EFFECTIVE MATURITY DIVERSIFICATION (% of Fund's net assets) Days 1-7 67.6 8-30 17.0 31-60 4.1 61-90 6.3 91-180 2.1 >180 4.3 Repurchase Agreements 50.7 U.S. Treasury Obligations 50.7 ASSET ALLOCATION (% of Fund's net assets) Repurchase Agreements - 50.7 U.S. Treasury Obligations - 50.7 Net Other Assets (Liabilities) - (1.4)% | |||||||||
| Fidelity Tax-Exempt Money Market Fund - Capital Reserves Class | ||||||||||
| Shareholder Report [Line Items] | ||||||||||
| Fund Name | Fidelity® Tax-Exempt Money Market Fund | |||||||||
| Class Name | Fidelity® Tax-Exempt Money Market Fund Capital Reserves Class | |||||||||
| Trading Symbol | FERXX | |||||||||
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Tax-Exempt Money Market Fund for the period November 1, 2024 to April 30, 2025. | |||||||||
| 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 1-877-208-0098 or by sending an e-mail to funddocuments@fmr.com. | |||||||||
| Additional Information Phone Number | 1-877-208-0098 | |||||||||
| Additional Information Email | funddocuments@fmr.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)
|
|||||||||
| Expenses Paid, Amount | $ 47 | |||||||||
| Expense Ratio, Percent | 0.95% | |||||||||
| Net Assets | $ 4,137,428,142 | |||||||||
| Holdings Count | shares | 645 | |||||||||
| Additional Fund Statistics [Text Block] | Key Fund Statistics
(as of April 30, 2025)
|
|||||||||
| Holdings [Text Block] | EFFECTIVE MATURITY DIVERSIFICATION (% of Fund's net assets) Days 1-7 78.6 8-30 2.0 31-60 6.5 61-90 2.6 91-180 6.1 >180 4.8 Variable Rate Demand Notes (VRDNs) 40.8 Tender Option Bond 27.6 Municipal Securities 13.4 Commercial Paper 7.1 Net Other Assets (Liabilities) 11.1 ASSET ALLOCATION (% of Fund's net assets) Variable Rate Demand Notes (VRDNs) - 40.8 Tender Option Bond - 27.6 Municipal Securities - 13.4 Commercial Paper - 7.1 Net Other Assets (Liabilities) - 11.1 |