Fidelity Central Investment Portfolios II N-CSR21 Nov 24Certified annual shareholder report (management investment company)Financial data

Company Profile

Form N-CSR Cover

Form N-CSR Cover	12 Months Ended
Form N-CSR Cover	Sep. 30, 2024
Shareholder Report [Line Items]
Document Type	N-CSR
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	Sep. 30, 2024

Shareholder Report

Shareholder Report	12 Months Ended
Shareholder Report	Sep. 30, 2024 USD ($) shares
Shareholder Report [Line Items]
Document Type	N-CSR
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	Sep. 30, 2024
Fidelity Investment Grade Bond Central Fund
Shareholder Report [Line Items]
Fund Name	Fidelity® Investment Grade Bond Central Fund
Class Name	Fidelity® Investment Grade Bond Central Fund
No Trading Symbol Flag	true
Annual or Semi-Annual Statement [Text Block]	This annual shareholder report contains information about Fidelity® Investment Grade Bond Central Fund for the period October 1, 2023 to September 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.
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 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® Investment Grade Bond Central Fund $ A 0.00 % B A Amount represents less than $.50 B Amount represents less than 0.005%
Expenses Paid, Amount	$ 0
Expense Ratio, Percent	0%
Factors Affecting Performance [Text Block]	What affected the Fund's performance this period? • • • • • •
Performance Past Does Not Indicate Future [Text]	The Fund's past performance is not a good predictor of the Fund's future performance.</span>" id="sjs-B25"><span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;">The Fund's past performance is not a good predictor of the Fund's future performance.</span>
Line Graph [Table Text Block]	How did the Fund perform over the past 10 years? CUMULATIVE PERFORMANCE September 30, 2014 through September 30, 2024. Initial investment of $10,000. Fidelity® Investment Grade Bond Central Fund $10,000 $10,190 $10,935 $11,101 $11,049 $12,236 $13,245 $13,401 $11,506 $11,671 $13,114 Bloomberg U.S. Aggregate Bond Index $10,000 $10,294 $10,829 $10,836 $10,705 $11,807 $12,632 $12,518 $10,691 $10,760 $12,004 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024
Average Annual Return [Table Text Block]	AVERAGE ANNUAL TOTAL RETURNS: 1 Year 5 Year 10 Year Fidelity® Investment Grade Bond Central Fund 12.37% 1.40% 2.75% Bloomberg U.S. Aggregate Bond Index 11.57% 0.33% 1.84% Visit www.fidelity.com for more recent performance information. The Fund's past performance is not a good predictor of the Fund's future performance. The graph and table do not reflect the deduction of taxes that a shareholder would pay on fund distributions or redemption of fund shares.
No Deduction of Taxes [Text Block]	The graph and table do not reflect the deduction of taxes that a shareholder would pay on fund distributions or redemption of fund shares.
Net Assets	$ 41,003,302,425
Holdings Count \| shares	4,835
Advisory Fees Paid, Amount	$ 0
Investment Company Portfolio Turnover	206%
Additional Fund Statistics [Text Block]	Key Fund Statistics (as of September 30, 2024) KEY FACTS Fund Size $ Number of Holdings 4,835 Total Advisory Fee $ Portfolio Turnover 206 %
Holdings [Text Block]	U.S. Government and U.S. Government Agency Obligations 60.7 AAA 9.8 AA 0.8 A 8.0 BBB 19.2 BB 2.1 B 0.8 Not Rated 3.8 QUALITY DIVERSIFICATION (% of Fund's net assets) Short-Term Investments and Net Other Assets (Liabilities) - (5.2)% 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. U.S. Treasury Obligations 43.0 Corporate Bonds 27.7 U.S. Government Agency - Mortgage Securities 17.7 Asset-Backed Securities 8.8 CMOs and Other Mortgage Related Securities 7.6 Foreign Government and Government Agency Obligations 0.2 Other Investments 0.1 Municipal Securities 0.1 Purchased Options 0.0 ASSET ALLOCATION (% of Fund's net assets) Short-Term Investments and Net Other Assets (Liabilities) - (5.2)% United States 90.5 Grand Cayman (UK Overseas Ter) 4.1 Mexico 0.8 United Kingdom 0.8 Ireland 0.6 Belgium 0.6 Bailiwick Of Jersey 0.6 Germany 0.5 Switzerland 0.4 Others 1.1 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets)
Largest Holdings [Text Block]	TOP HOLDINGS (% of Fund's net assets) US Treasury Notes 31.6 US Treasury Bonds 11.4 Fannie Mae Mortgage pass-thru certificates 5.7 Ginnie Mae II Pool 4.8 Freddie Mac Gold Pool 4.2 Uniform Mortgage Backed Securities 2.3 JPMorgan Chase & Co 1.5 Freddie Mac Multifamily Structured pass-thru certificates 1.4 Morgan Stanley 1.3 Bank of America Corp 1.0 65.2
Material Fund Change [Text Block]	How has the Fund changed? This is a summary of certain changes to the Fund since October 1, 2023. For more complete information, you may review the Fund's next prospectus, which we expect to be available by November 29, 2024 at fundresearch.fidelity.com/prospectus/sec or upon request at 1-800-544-8544 . Effective March 1, 2024, the fund's management contract was amended to remove the fee the investment adviser received from investing funds.
Material Fund Change Expenses [Text Block]	Effective March 1, 2024, the fund's management contract was amended to remove the fee the investment adviser received from investing funds.
Summary of Change Legend [Text Block]	This is a summary of certain changes to the Fund since October 1, 2023. For more complete information, you may review the Fund's next prospectus, which we expect to be available by November 29, 2024 at fundresearch.fidelity.com/prospectus/sec or upon request at 1-800-544-8544 .
Updated Prospectus Phone Number	1-800-544-8544</span>" id="sjs-B39"><span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;">1-800-544-8544</span>
Updated Prospectus Web Address	fundresearch.fidelity.com/prospectus/sec</span>" id="sjs-B40"><span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:bold;">fundresearch.fidelity.com/prospectus/sec</span>
Fidelity Inflation-Protected Bond Index Central Fund
Shareholder Report [Line Items]
Fund Name	Fidelity® Inflation-Protected Bond Index Central Fund
Class Name	Fidelity® Inflation-Protected Bond Index Central Fund
No Trading Symbol Flag	true
Annual or Semi-Annual Statement [Text Block]	This annual shareholder report contains information about Fidelity® Inflation-Protected Bond Index Central Fund for the period October 1, 2023 to September 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.
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 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® Inflation-Protected Bond Index Central Fund $ A 0.00 % B A Amount represents less than $.50 B Amount represents less than 0.005%
Expenses Paid, Amount	$ 0
Expense Ratio, Percent	0%
Factors Affecting Performance [Text Block]	What affected the Fund's performance this period? • •
Performance Past Does Not Indicate Future [Text]	The Fund's past performance is not a good predictor of the Fund's future performance.</span>" id="sjs-B56"><span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;">The Fund's past performance is not a good predictor of the Fund's future performance.</span>
Line Graph [Table Text Block]	How did the Fund perform over the past 10 years? CUMULATIVE PERFORMANCE September 30, 2014 through September 30, 2024. Initial investment of $10,000. Fidelity® Inflation-Protected Bond Index Central Fund $10,000 $9,914 $10,402 $10,374 $10,414 $11,022 $11,854 $12,535 $11,598 $11,847 $12,915 Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) 1-10 Year Index $10,000 $9,918 $10,397 $10,383 $10,416 $11,015 $11,869 $12,551 $11,617 $11,862 $12,931 Bloomberg U.S. Aggregate Bond Index $10,000 $10,294 $10,829 $10,836 $10,705 $11,807 $12,632 $12,518 $10,691 $10,760 $12,004 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024
Average Annual Return [Table Text Block]	AVERAGE ANNUAL TOTAL RETURNS: 1 Year 5 Year 10 Year Fidelity® Inflation-Protected Bond Index Central Fund 9.01% 3.22% 2.59% Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) 1-10 Year Index 9.01% 3.26% 2.60% Bloomberg U.S. Aggregate Bond Index 11.57% 0.33% 1.84% Visit www.fidelity.com for more recent performance information. The Fund's past performance is not a good predictor of the Fund's future performance. The graph and table do not reflect the deduction of taxes that a shareholder would pay on fund distributions or redemption of fund shares.
No Deduction of Taxes [Text Block]	The graph and table do not reflect the deduction of taxes that a shareholder would pay on fund distributions or redemption of fund shares.
Net Assets	$ 442,456,808
Holdings Count \| shares	35
Advisory Fees Paid, Amount	$ 0
Investment Company Portfolio Turnover	63%
Additional Fund Statistics [Text Block]	Key Fund Statistics (as of September 30, 2024) KEY FACTS Fund Size $ Number of Holdings 35 Total Advisory Fee $ Portfolio Turnover 63 %
Holdings [Text Block]	COUPON DISTRIBUTION (% of Fund's net assets) 0.01 - 0.99% 58.2 1 - 1.99% 24.9 2 - 2.99% 11.7 3 - 3.99% 4.8 U.S. Treasury Obligations 99.6 Short-Term Investments and Net Other Assets (Liabilities) 0.4 ASSET ALLOCATION (% of Fund's net assets)
Largest Holdings [Text Block]	TOP HOLDINGS (% of Fund's net assets) US Treasury Notes 88.3 US Treasury Bonds 11.3 99.6
Material Fund Change [Text Block]	How has the Fund changed? This is a summary of certain changes to the Fund since October 1, 2023. For more complete information, you may review the Fund's next prospectus, which we expect to be available by November 29, 2024 at fundresearch.fidelity.com/prospectus/sec or upon request at 1-800-544-8544 . Effective March 1, 2024, the fund's management contract was amended to remove the fee the investment adviser received from investing funds.
Material Fund Change Expenses [Text Block]	Effective March 1, 2024, the fund's management contract was amended to remove the fee the investment adviser received from investing funds.
Summary of Change Legend [Text Block]	This is a summary of certain changes to the Fund since October 1, 2023. For more complete information, you may review the Fund's next prospectus, which we expect to be available by November 29, 2024 at fundresearch.fidelity.com/prospectus/sec or upon request at 1-800-544-8544 .
Updated Prospectus Phone Number	1-800-544-8544</span>" id="sjs-B70"><span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;">1-800-544-8544</span>
Updated Prospectus Web Address	fundresearch.fidelity.com/prospectus/sec</span>" id="sjs-B71"><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, Line Graph

Shareholder Report, Line Graph (Details) - USD ($)

12 Months Ended

60 Months Ended

120 Months Ended

132 Months Ended

Sep. 30, 2024

Sep. 30, 2023

Sep. 30, 2022

Sep. 30, 2021

Sep. 30, 2020

Sep. 30, 2019

Sep. 30, 2018

Sep. 30, 2017

Sep. 30, 2016

Sep. 30, 2015

Sep. 30, 2014

C000052072_0_BBIndexMember_1YRMember

Account Value [Line Items]

Average Annual Return, Percent

11.57%

C000052072_0_BBIndexMember_5YRMember

Account Value [Line Items]

Average Annual Return, Percent

0.33%

C000052072_0_BBIndexMember_10YRMember

Account Value [Line Items]

Average Annual Return, Percent

1.84%

C000113010_1_BBIndexMember_1YRMember

Account Value [Line Items]

Average Annual Return, Percent

11.57%

C000113010_1_BBIndexMember_5YRMember

Account Value [Line Items]

Average Annual Return, Percent

0.33%

C000113010_1_BBIndexMember_10YRMember

Account Value [Line Items]

Average Annual Return, Percent

1.84%

C000052072_LG_ClassMember_11YRMember

Account Value [Line Items]

Line Graph and Table Measure Name

Fidelity® Investment Grade Bond Central Fund" id="sjs-E23">Fidelity® Investment Grade Bond Central Fund

C000052072_ClassMember_AsOf_2014Member

Account Value [Line Items]

Account Value

$ 10,000

C000052072_ClassMember_AsOf_2015Member

Account Value [Line Items]

Account Value

$ 10,190

C000052072_ClassMember_AsOf_2016Member

Account Value [Line Items]

Account Value

$ 10,935

C000052072_ClassMember_AsOf_2017Member

Account Value [Line Items]

Account Value

$ 11,101

C000052072_ClassMember_AsOf_2018Member

Account Value [Line Items]

Account Value

$ 11,049

C000052072_ClassMember_AsOf_2019Member

Account Value [Line Items]

Account Value

$ 12,236

C000052072_ClassMember_AsOf_2020Member

Account Value [Line Items]

Account Value

$ 13,245

C000052072_ClassMember_AsOf_2021Member

Account Value [Line Items]

Account Value

$ 13,401

C000052072_ClassMember_AsOf_2022Member

Account Value [Line Items]

Account Value

$ 11,506

C000052072_ClassMember_AsOf_2023Member

Account Value [Line Items]

Account Value

$ 11,671

C000052072_ClassMember_AsOf_2024Member

Account Value [Line Items]

Account Value

$ 13,114

C000052072_LG_1_AdditionalIndexMember_11YRMember

Account Value [Line Items]

Line Graph and Table Measure Name

Bloomberg U.S. Aggregate Bond Index" id="sjs-E59">Bloomberg U.S. Aggregate Bond Index

C000052072_1_AdditionalIndexMember_AsOf_2014Member

Account Value [Line Items]

Account Value

10,000

C000052072_1_AdditionalIndexMember_AsOf_2015Member

Account Value [Line Items]

Account Value

10,294

C000052072_1_AdditionalIndexMember_AsOf_2016Member

Account Value [Line Items]

Account Value

10,829

C000052072_1_AdditionalIndexMember_AsOf_2017Member

Account Value [Line Items]

Account Value

10,836

C000052072_1_AdditionalIndexMember_AsOf_2018Member

Account Value [Line Items]

Account Value

10,705

C000052072_1_AdditionalIndexMember_AsOf_2019Member

Account Value [Line Items]

Account Value

11,807

C000052072_1_AdditionalIndexMember_AsOf_2020Member

Account Value [Line Items]

Account Value

12,632

C000052072_1_AdditionalIndexMember_AsOf_2021Member

Account Value [Line Items]

Account Value

12,518

C000052072_1_AdditionalIndexMember_AsOf_2022Member

Account Value [Line Items]

Account Value

10,691

C000052072_1_AdditionalIndexMember_AsOf_2023Member

Account Value [Line Items]

Account Value

10,760

C000052072_1_AdditionalIndexMember_AsOf_2024Member

Account Value [Line Items]

Account Value

$ 12,004

C000052072_NoLoadClassMember_1YRMember

Account Value [Line Items]

Average Annual Return, Percent

12.37%

C000052072_NoLoadClassMember_5YRMember

Account Value [Line Items]

Average Annual Return, Percent

1.40%

C000052072_NoLoadClassMember_10YRMember

Account Value [Line Items]

Average Annual Return, Percent

2.75%

C000113010_LG_ClassMember_11YRMember

Account Value [Line Items]

Line Graph and Table Measure Name

Fidelity® Inflation-Protected Bond Index Central Fund" id="sjs-E104">Fidelity® Inflation-Protected Bond Index Central Fund

C000113010_ClassMember_AsOf_2014Member

Account Value [Line Items]

Account Value

10,000

C000113010_ClassMember_AsOf_2015Member

Account Value [Line Items]

Account Value

9,914

C000113010_ClassMember_AsOf_2016Member

Account Value [Line Items]

Account Value

10,402

C000113010_ClassMember_AsOf_2017Member

Account Value [Line Items]

Account Value

10,374

C000113010_ClassMember_AsOf_2018Member

Account Value [Line Items]

Account Value

10,414

C000113010_ClassMember_AsOf_2019Member

Account Value [Line Items]

Account Value

11,022

C000113010_ClassMember_AsOf_2020Member

Account Value [Line Items]

Account Value

11,854

C000113010_ClassMember_AsOf_2021Member

Account Value [Line Items]

Account Value

12,535

C000113010_ClassMember_AsOf_2022Member

Account Value [Line Items]

Account Value

11,598

C000113010_ClassMember_AsOf_2023Member

Account Value [Line Items]

Account Value

11,847

C000113010_ClassMember_AsOf_2024Member

Account Value [Line Items]

Account Value

$ 12,915

C000113010_LG_1_AdditionalIndexMember_11YRMember

Account Value [Line Items]

Line Graph and Table Measure Name

Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) 1-10 Year Index" id="sjs-E140">Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) 1-10 Year Index

C000113010_1_AdditionalIndexMember_AsOf_2014Member

Account Value [Line Items]

Account Value

10,000

C000113010_1_AdditionalIndexMember_AsOf_2015Member

Account Value [Line Items]

Account Value

9,918

C000113010_1_AdditionalIndexMember_AsOf_2016Member

Account Value [Line Items]

Account Value

10,397

C000113010_1_AdditionalIndexMember_AsOf_2017Member

Account Value [Line Items]

Account Value

10,383

C000113010_1_AdditionalIndexMember_AsOf_2018Member

Account Value [Line Items]

Account Value

10,416

C000113010_1_AdditionalIndexMember_AsOf_2019Member

Account Value [Line Items]

Account Value

11,015

C000113010_1_AdditionalIndexMember_AsOf_2020Member

Account Value [Line Items]

Account Value

11,869

C000113010_1_AdditionalIndexMember_AsOf_2021Member

Account Value [Line Items]

Account Value

12,551

C000113010_1_AdditionalIndexMember_AsOf_2022Member

Account Value [Line Items]

Account Value

11,617

C000113010_1_AdditionalIndexMember_AsOf_2023Member

Account Value [Line Items]

Account Value

11,862

C000113010_1_AdditionalIndexMember_AsOf_2024Member

Account Value [Line Items]

Account Value

12,931

$ 12,931

C000113010_LG_2_AdditionalIndexMember_11YRMember

Account Value [Line Items]

Line Graph and Table Measure Name

Bloomberg U.S. Aggregate Bond Index" id="sjs-E176">Bloomberg U.S. Aggregate Bond Index

C000113010_2_AdditionalIndexMember_AsOf_2014Member

Account Value [Line Items]

Account Value

$ 10,000

C000113010_2_AdditionalIndexMember_AsOf_2015Member

Account Value [Line Items]

Account Value

$ 10,294

C000113010_2_AdditionalIndexMember_AsOf_2016Member

Account Value [Line Items]

Account Value

$ 10,829

C000113010_2_AdditionalIndexMember_AsOf_2017Member

Account Value [Line Items]

Account Value

$ 10,836

C000113010_2_AdditionalIndexMember_AsOf_2018Member

Account Value [Line Items]

Account Value

$ 10,705

C000113010_2_AdditionalIndexMember_AsOf_2019Member

Account Value [Line Items]

Account Value

$ 11,807

C000113010_2_AdditionalIndexMember_AsOf_2020Member

Account Value [Line Items]

Account Value

$ 12,632

C000113010_2_AdditionalIndexMember_AsOf_2021Member

Account Value [Line Items]

Account Value

$ 12,518

C000113010_2_AdditionalIndexMember_AsOf_2022Member

Account Value [Line Items]

Account Value

$ 10,691

C000113010_2_AdditionalIndexMember_AsOf_2023Member

Account Value [Line Items]

Account Value

$ 10,760

C000113010_2_AdditionalIndexMember_AsOf_2024Member

Account Value [Line Items]

Account Value

$ 12,004

C000113010_NoLoadClassMember_1YRMember

Account Value [Line Items]

Average Annual Return, Percent

9.01%

C000113010_NoLoadClassMember_5YRMember

Account Value [Line Items]

Average Annual Return, Percent

3.22%

C000113010_NoLoadClassMember_10YRMember

Account Value [Line Items]

Average Annual Return, Percent

2.59%

C000113010_0_AdditionalIndexMember_1YRMember

Account Value [Line Items]

Average Annual Return, Percent

9.01%

C000113010_0_AdditionalIndexMember_5YRMember

Account Value [Line Items]

Average Annual Return, Percent

3.26%

C000113010_0_AdditionalIndexMember_10YRMember

Account Value [Line Items]

Average Annual Return, Percent

2.60%

Shareholder Report, Holdings (D

Shareholder Report, Holdings (Details)	Sep. 30, 2024
Fidelity Investment Grade Bond Central Fund \| TH0Member
Holdings [Line Items]
Percent of Net Asset Value	31.60%
Fidelity Investment Grade Bond Central Fund \| TH1Member
Holdings [Line Items]
Percent of Net Asset Value	11.40%
Fidelity Investment Grade Bond Central Fund \| TH2Member
Holdings [Line Items]
Percent of Net Asset Value	5.70%
Fidelity Investment Grade Bond Central Fund \| TH3Member
Holdings [Line Items]
Percent of Net Asset Value	4.80%
Fidelity Investment Grade Bond Central Fund \| TH4Member
Holdings [Line Items]
Percent of Net Asset Value	4.20%
Fidelity Investment Grade Bond Central Fund \| TH5Member
Holdings [Line Items]
Percent of Net Asset Value	2.30%
Fidelity Investment Grade Bond Central Fund \| TH6Member
Holdings [Line Items]
Percent of Net Asset Value	1.50%
Fidelity Investment Grade Bond Central Fund \| TH7Member
Holdings [Line Items]
Percent of Net Asset Value	1.40%
Fidelity Investment Grade Bond Central Fund \| TH8Member
Holdings [Line Items]
Percent of Net Asset Value	1.30%
Fidelity Investment Grade Bond Central Fund \| TH9Member
Holdings [Line Items]
Percent of Net Asset Value	1%
Fidelity Investment Grade Bond Central Fund \| QDUSGovernmentandUSGovernmentAgencyObligationsMember
Holdings [Line Items]
Percent of Net Asset Value	60.70%
Fidelity Investment Grade Bond Central Fund \| QDAAAMember
Holdings [Line Items]
Percent of Net Asset Value	9.80%
Fidelity Investment Grade Bond Central Fund \| QDAAMember
Holdings [Line Items]
Percent of Net Asset Value	0.80%
Fidelity Investment Grade Bond Central Fund \| QDAMember
Holdings [Line Items]
Percent of Net Asset Value	8%
Fidelity Investment Grade Bond Central Fund \| QDBBBMember
Holdings [Line Items]
Percent of Net Asset Value	19.20%
Fidelity Investment Grade Bond Central Fund \| QDBBMember
Holdings [Line Items]
Percent of Net Asset Value	2.10%
Fidelity Investment Grade Bond Central Fund \| QDBMember
Holdings [Line Items]
Percent of Net Asset Value	0.80%
Fidelity Investment Grade Bond Central Fund \| QDNotRatedMember
Holdings [Line Items]
Percent of Net Asset Value	3.80%
Fidelity Investment Grade Bond Central Fund \| United States
Holdings [Line Items]
Percent of Net Asset Value	90.50%
Fidelity Investment Grade Bond Central Fund \| GrandCaymanUKOverseasTerMember
Holdings [Line Items]
Percent of Net Asset Value	4.10%
Fidelity Investment Grade Bond Central Fund \| Mexico
Holdings [Line Items]
Percent of Net Asset Value	0.80%
Fidelity Investment Grade Bond Central Fund \| United Kingdom
Holdings [Line Items]
Percent of Net Asset Value	0.80%
Fidelity Investment Grade Bond Central Fund \| Ireland
Holdings [Line Items]
Percent of Net Asset Value	0.60%
Fidelity Investment Grade Bond Central Fund \| Belgium
Holdings [Line Items]
Percent of Net Asset Value	0.60%
Fidelity Investment Grade Bond Central Fund \| BailiwickOfJerseyMember
Holdings [Line Items]
Percent of Net Asset Value	0.60%
Fidelity Investment Grade Bond Central Fund \| Germany
Holdings [Line Items]
Percent of Net Asset Value	0.50%
Fidelity Investment Grade Bond Central Fund \| Switzerland
Holdings [Line Items]
Percent of Net Asset Value	0.40%
Fidelity Investment Grade Bond Central Fund \| OtherMember
Holdings [Line Items]
Percent of Net Asset Value	1.10%
Fidelity Investment Grade Bond Central Fund \| AAUSTreasuryObligationsMember
Holdings [Line Items]
Percent of Net Asset Value	43%
Fidelity Investment Grade Bond Central Fund \| AACorporateBondsMember
Holdings [Line Items]
Percent of Net Asset Value	27.70%
Fidelity Investment Grade Bond Central Fund \| AAUSGovernmentAgencyMortgageSecuritiesMember
Holdings [Line Items]
Percent of Net Asset Value	17.70%
Fidelity Investment Grade Bond Central Fund \| AAAssetBackedSecuritiesMember
Holdings [Line Items]
Percent of Net Asset Value	8.80%
Fidelity Investment Grade Bond Central Fund \| AACMOsandOtherMortgageRelatedSecuritiesMember
Holdings [Line Items]
Percent of Net Asset Value	7.60%
Fidelity Investment Grade Bond Central Fund \| AAForeignGovernmentandGovernmentAgencyObligationsMember
Holdings [Line Items]
Percent of Net Asset Value	0.20%
Fidelity Investment Grade Bond Central Fund \| AAOtherInvestmentsMember
Holdings [Line Items]
Percent of Net Asset Value	0.10%
Fidelity Investment Grade Bond Central Fund \| AAMunicipalSecuritiesMember
Holdings [Line Items]
Percent of Net Asset Value	0.10%
Fidelity Investment Grade Bond Central Fund \| AAPurchasedOptionsMember
Holdings [Line Items]
Percent of Net Asset Value	0%
Fidelity Inflation-Protected Bond Index Central Fund \| TH0Member
Holdings [Line Items]
Percent of Net Asset Value	88.30%
Fidelity Inflation-Protected Bond Index Central Fund \| TH1Member
Holdings [Line Items]
Percent of Net Asset Value	11.30%
Fidelity Inflation-Protected Bond Index Central Fund \| CD0Member
Holdings [Line Items]
Percent of Net Asset Value	58.20%
Fidelity Inflation-Protected Bond Index Central Fund \| CD1Member
Holdings [Line Items]
Percent of Net Asset Value	24.90%
Fidelity Inflation-Protected Bond Index Central Fund \| CD2Member
Holdings [Line Items]
Percent of Net Asset Value	11.70%
Fidelity Inflation-Protected Bond Index Central Fund \| CD3Member
Holdings [Line Items]
Percent of Net Asset Value	4.80%
Fidelity Inflation-Protected Bond Index Central Fund \| AAUSTreasuryObligationsMember
Holdings [Line Items]
Percent of Net Asset Value	99.60%
Fidelity Inflation-Protected Bond Index Central Fund \| AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember
Holdings [Line Items]
Percent of Net Asset Value	0.40%