| Form N-CSR Cover | 6 Months Ended |
| Jun. 30, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Fidelity Central Investment Portfolios II LLC |
| Entity Central Index Key | 0001401097 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Jun. 30, 2024 |
| Shareholder Report | 6 Months Ended |
| Jun. 30, 2024 USD ($) shares | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Fidelity Central Investment Portfolios II LLC |
| Entity Central Index Key | 0001401097 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Jun. 30, 2024 |
| Fidelity International Credit Central Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® International Credit Central Fund |
| Class Name | Fidelity® International Credit Central Fund |
| No Trading Symbol Flag | true |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® International Credit Central Fund for the period January 1, 2024 to June 30, 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. |
| Additional Information Phone Number | 1-800-544-8544 |
| 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® International Credit Central Fund $ A 0.01 % A Amount represents less than $.50 |
| Expenses Paid, Amount | $ 0 |
| Expense Ratio, Percent | 0.01% |
| Net Assets | $ 92,142,306 |
| Holdings Count | shares | 188 |
| Investment Company Portfolio Turnover | 103% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of June 30, 2024) KEY FACTS Fund Size $ Number of Holdings 188 Portfolio Turnover 103 % |
| Holdings [Text Block] | U.S. Government and U.S. Government Agency Obligations 21.2 AAA 3.6 AA 0.5 A 11.9 BBB 36.5 BB 6.2 B 0.6 CCC,CC,C 0.3 D 0.7 Not Rated 12.4 Short-Term Investments and Net Other Assets (Liabilities) 6.1 QUALITY DIVERSIFICATION (% of Fund's net assets) We have used ratings from Moody's Investors Service, Inc. Where Moody's® ratings are not available, we have used S&P® ratings. All ratings are as of the date indicated and do not reflect subsequent changes. Corporate Bonds 54.5 U.S. Treasury Obligations 21.2 Preferred Securities 9.8 Foreign Government and Government Agency Obligations 8.4 Short-Term Investments and Net Other Assets (Liabilities) 6.1 ASSET ALLOCATION (% of Fund's net assets) United States 30.6 United Kingdom 20.9 Germany 19.2 Switzerland 4.7 France 4.7 Netherlands 3.7 Luxembourg 3.0 Australia 2.0 Ireland 1.6 Others 9.6 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) US Treasury Notes 13.0 US Treasury Bonds 8.2 German Federal Republic 7.9 NatWest Group PLC 2.2 Lloyds Banking Group PLC 2.2 UBS Group AG 2.0 Barclays PLC 2.0 HSBC Holdings PLC 2.0 Deutsche Bank AG 1.9 ING Groep NV 1.9 43.3 |
| Shareholder Report, Holdings (Details) - Fidelity International Credit Central Fund | Jun. 30, 2024 |
| TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13% |
| TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.20% |
| TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.90% |
| TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| QDUSGovernmentandUSGovernmentAgencyObligationsMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 21.20% |
| QDAMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.90% |
| QDBBBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 36.50% |
| QDBBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.20% |
| QDBMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| QDCCCCCCMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| QDDMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| QDNotRatedMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.40% |
| QDShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.10% |
| United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 30.60% |
| United Kingdom | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 20.90% |
| Germany | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.20% |
| Switzerland | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.70% |
| France | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.70% |
| Netherlands | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| Luxembourg | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| Australia | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| Ireland | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| OtherMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.60% |
| AACorporateBondsMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 54.50% |
| AAUSTreasuryObligationsMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 21.20% |
| AAPreferredSecuritiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.80% |
| AAForeignGovernmentandGovernmentAgencyObligationsMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.40% |
| AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.10% |
| Label | Element | Value |
| C000192458 [Member] | QDAAAMember [Member] | ||
| Percent of Net Asset Value | oef_PctOfNav | 3.60% |
| C000192458 [Member] | QDAAMember [Member] | ||
| Percent of Net Asset Value | oef_PctOfNav | 0.50% |
