| Form N-CSR Cover | 6 Months Ended |
| Aug. 31, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Fidelity California Municipal Trust II |
| Entity Central Index Key | 0000878662 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Aug. 31, 2024 |
| Shareholder Report | 6 Months Ended |
| Aug. 31, 2024 USD ($) shares | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Fidelity California Municipal Trust II |
| Entity Central Index Key | 0000878662 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Aug. 31, 2024 |
| Fidelity California Municipal Money Market Fund - Premium Class | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® California Municipal Money Market Fund |
| Class Name | Fidelity® California Municipal Money Market Fund Premium Class |
| Trading Symbol | FSPXX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® California Municipal Money Market Fund for the period March 1, 2024 to August 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 Premium Class $ 0.30 % |
| Expenses Paid, Amount | $ 15 |
| Expense Ratio, Percent | 0.30% |
| Net Assets | $ 5,189,118,446 |
| Holdings Count | shares | 458 |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of August 31, 2024) KEY FACTS Fund Size $ Number of Holdings 458 |
| Holdings [Text Block] | EFFECTIVE MATURITY DIVERSIFICATION (% of Fund's net assets) Days 1-7 71.8 8-30 1.4 31-60 11.3 61-90 7.5 91-180 2.3 >180 6.1 Variable Rate Demand Notes (VRDNs) 40.4 Tender Option Bond 19.4 Commercial Paper 17.4 Municipal Securities 12.8 Net Other Assets (Liabilities) 10.0 ASSET ALLOCATION (% of Fund's net assets) |
| Fidelity California Municipal Money Market Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® California Municipal Money Market Fund |
| Class Name | Fidelity® California Municipal Money Market Fund |
| Trading Symbol | FABXX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® California Municipal Money Market Fund for the period March 1, 2024 to August 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® California Municipal Money Market Fund $ 0.42 % |
| Expenses Paid, Amount | $ 21 |
| Expense Ratio, Percent | 0.42% |
| Net Assets | $ 5,189,118,446 |
| Holdings Count | shares | 458 |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of August 31, 2024) KEY FACTS Fund Size $ Number of Holdings 458 |
| Holdings [Text Block] | EFFECTIVE MATURITY DIVERSIFICATION (% of Fund's net assets) Days 1-7 71.8 8-30 1.4 31-60 11.3 61-90 7.5 91-180 2.3 >180 6.1 Variable Rate Demand Notes (VRDNs) 40.4 Tender Option Bond 19.4 Commercial Paper 17.4 Municipal Securities 12.8 Net Other Assets (Liabilities) 10.0 ASSET ALLOCATION (% of Fund's net assets) |
| Fidelity California Municipal Money Market Fund - Institutional Class | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® California Municipal Money Market Fund |
| Class Name | Fidelity® California Municipal Money Market Fund Institutional Class |
| Trading Symbol | FSBXX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® California Municipal Money Market Fund for the period March 1, 2024 to August 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 1-877-208-0098 or by sending an e-mail to fidfunddocuments@fidelity.com. |
| Additional Information Phone Number | 1-877-208-0098 |
| 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 Institutional Class $ 0.20 % |
| Expenses Paid, Amount | $ 10 |
| Expense Ratio, Percent | 0.20% |
| Net Assets | $ 5,189,118,446 |
| Holdings Count | shares | 458 |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of August 31, 2024) KEY FACTS Fund Size $ Number of Holdings 458 |
| Holdings [Text Block] | EFFECTIVE MATURITY DIVERSIFICATION (% of Fund's net assets) Days 1-7 71.8 8-30 1.4 31-60 11.3 61-90 7.5 91-180 2.3 >180 6.1 Variable Rate Demand Notes (VRDNs) 40.4 Tender Option Bond 19.4 Commercial Paper 17.4 Municipal Securities 12.8 Net Other Assets (Liabilities) 10.0 ASSET ALLOCATION (% of Fund's net assets) |
| Shareholder Report, Holdings (Details) | Aug. 31, 2024 |
| Fidelity California Municipal Money Market Fund - Premium Class | EMD0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 71.80% |
| Fidelity California Municipal Money Market Fund - Premium Class | EMD1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| Fidelity California Municipal Money Market Fund - Premium Class | EMD2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.30% |
| Fidelity California Municipal Money Market Fund - Premium Class | EMD3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.50% |
| Fidelity California Municipal Money Market Fund - Premium Class | EMD4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| Fidelity California Municipal Money Market Fund - Premium Class | EMD5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.10% |
| Fidelity California Municipal Money Market Fund - Premium Class | AAVariableRateDemandNotesVRDNsMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 40.40% |
| Fidelity California Municipal Money Market Fund - Premium Class | AATenderOptionBondMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.40% |
| Fidelity California Municipal Money Market Fund - Premium Class | AACommercialPaperMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.40% |
| Fidelity California Municipal Money Market Fund - Premium Class | AAMunicipalSecuritiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.80% |
| Fidelity California Municipal Money Market Fund - Premium Class | AANetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10% |
| Fidelity California Municipal Money Market Fund | EMD0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 71.80% |
| Fidelity California Municipal Money Market Fund | EMD1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| Fidelity California Municipal Money Market Fund | EMD2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.30% |
| Fidelity California Municipal Money Market Fund | EMD3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.50% |
| Fidelity California Municipal Money Market Fund | EMD4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| Fidelity California Municipal Money Market Fund | EMD5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.10% |
| Fidelity California Municipal Money Market Fund | AAVariableRateDemandNotesVRDNsMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 40.40% |
| Fidelity California Municipal Money Market Fund | AATenderOptionBondMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.40% |
| Fidelity California Municipal Money Market Fund | AACommercialPaperMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.40% |
| Fidelity California Municipal Money Market Fund | AAMunicipalSecuritiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.80% |
| Fidelity California Municipal Money Market Fund | AANetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10% |
| Fidelity California Municipal Money Market Fund - Institutional Class | EMD0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 71.80% |
| Fidelity California Municipal Money Market Fund - Institutional Class | EMD1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| Fidelity California Municipal Money Market Fund - Institutional Class | EMD2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.30% |
| Fidelity California Municipal Money Market Fund - Institutional Class | EMD3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.50% |
| Fidelity California Municipal Money Market Fund - Institutional Class | EMD4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| Fidelity California Municipal Money Market Fund - Institutional Class | EMD5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.10% |
| Fidelity California Municipal Money Market Fund - Institutional Class | AAVariableRateDemandNotesVRDNsMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 40.40% |
| Fidelity California Municipal Money Market Fund - Institutional Class | AATenderOptionBondMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.40% |
| Fidelity California Municipal Money Market Fund - Institutional Class | AACommercialPaperMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.40% |
| Fidelity California Municipal Money Market Fund - Institutional Class | AAMunicipalSecuritiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.80% |
| Fidelity California Municipal Money Market Fund - Institutional Class | AANetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10% |
