Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	FIDELITY CHARLES STREET TRUST
NF_05.31 Fidelity Sustainable Multi-Asset Fund AMCIZ PRO -01 | Fidelity Sustainable Multi-Asset Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Summary Fund/Class:Fidelity® Sustainable Multi-Asset Fund/Fidelity Advisor® Sustainable Multi-Asset Fund A, M, C, I
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The fund seeks total return.
Expense [Heading]	rr_ExpenseHeading	Fee Table
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund. In addition to the fees and expenses described below, your broker may also require you to pay brokerage commissions on purchases and sales of certain share classes of the fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the fund or certain other Fidelity® funds. More information about these and other discounts is available from your investment professional and in the "Fund Distribution" section beginning on page 31 of the prospectus. Different intermediaries may provide additional waivers or reductions of the sales charge. Please see “Sales Charge Waiver Policies Applied by Certain Intermediaries” in the “Appendix” section of the prospectus.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Operating Expenses (expenses that you pay each year as a % of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	January 31, 2024
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The fund will not incur transaction costs, such as commissions, when it buys and sells shares of underlying Fidelity® funds (or "turns over" its portfolio), but it could incur transaction costs if it were to buy and sell other types of securities directly. If the fund were to buy and sell other types of securities directly, a higher portfolio turnover rate could indicate higher transaction costs and could result in higher taxes when fund shares are held in a taxable account. Such costs, if incurred, would not be reflected in annual operating expenses or in the example and would affect the fund's performance.
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the fund or certain other Fidelity® funds. More information about these and other discounts is available from your investment professional and in the "Fund Distribution" section beginning on page 31 of the prospectus.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 50,000
Other Expenses, New Fund, Based on Estimates [Text]	rr_OtherExpensesNewFundBasedOnEstimates	Based on estimated amounts for the current fiscal year.
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that your shareholder fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated and if you hold your shares:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Normally investing at least 80% of assets in Fidelity® funds (including mutual funds and exchange traded funds (ETFs)) that invest in securities of issuers that Fidelity Management & Research Company (the Adviser) believes have proven or improving sustainability practices based on an evaluation of such issuer’s individual environmental, social, and governance (ESG) profile and in Fidelity® index funds that track an ESG index (underlying Fidelity funds). Allocating assets according to a neutral asset allocation strategy in which 70% of the fund’s assets are allocated to underlying Fidelity® U.S. and international equity mutual funds and ETFs and 30% to underlying Fidelity® bond mutual funds and ETFs. To reflect the Adviser's market outlook, which is primarily focused on the intermediate term, the Adviser may overweight or underweight each asset class within the following ranges: equity funds (60%-80%) and bond funds (20%-40%). The Adviser may invest up to 10% of the fund’s total assets in commodities, high yield debt (also referred to as junk bonds), floating rate debt, real estate debt, international debt, emerging markets debt or short term funds, but no more than 25% in aggregate within those asset classes. Buying and selling futures contracts (both long and short positions) in an effort to manage cash flows efficiently, remain fully invested, or facilitate asset allocation. Actively managed underlying funds employ sustainable investing exclusion criteria to avoid investments in issuers that are directly engage in, and/or derive significant revenue from, certain industries. Please see “Fund Basics – Investment Details – Sustainable Investing Exclusions” for additional information.
Risk [Heading]	rr_RiskHeading	Principal Investment Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	Asset Allocation Risk. The fund is subject to risks resulting from the Adviser's asset allocation decisions. The selection of underlying funds and the allocation of the fund's assets among various asset classes could cause the fund to lose value or its results to lag relevant benchmarks or other funds with similar objectives. Investing in ETFs. ETFs may trade in the secondary market at prices below the value of their underlying portfolios and may not be liquid. ETFs that track an index are subject to tracking error and may be unable to sell poorly performing assets that are included in their index or other benchmark. Investing in Other Funds. The fund bears all risks of investment strategies employed by the underlying funds, including the risk that the underlying funds will not meet their investment objectives. Stock Market Volatility. Stock markets are volatile and can decline significantly in response to adverse issuer, political, regulatory, market, or economic developments. Different parts of the market, including different market sectors, and different types of securities can react differently to these developments. Interest Rate Changes. Interest rate increases can cause the price of a debt security to decrease. Sustainability Risk. Application of FMR’s ESG ratings process and/or its sustainable investing exclusion criteria may affect the fund’s exposure to certain issuers, sectors, regions, and countries and may affect the fund’s performance depending on whether certain investments are in or out of favor. The criteria related to the fund’s ESG ratings process and/or adherence to its sustainable investing exclusion criteria may result in the fund forgoing opportunities to buy certain securities when it might otherwise be advantageous to do so, or selling securities for ESG reasons when it might be otherwise disadvantageous for it to do so. As a result, the fund's performance may at times be better or worse than the performance of funds that do not use ESG or sustainability criteria. There are significant differences in interpretations of what it means for an issuer to have positive ESG factors. While the Adviser believes its definitions are reasonable, the portfolio decisions it makes may differ with other investors’ or advisers’ views. Foreign and Emerging Market Risk. Foreign markets, particularly emerging markets, can be more volatile than the U.S. market due to increased risks of adverse issuer, political, regulatory, market, or economic developments and can perform differently from the U.S. market. The extent of economic development; political stability; market depth, infrastructure, and capitalization; and regulatory oversight can be less than in more developed markets. Emerging markets typically have less established legal, accounting and financial reporting systems than those in more developed markets, which may reduce the scope or quality of financial information available to investors. Emerging markets can be subject to greater social, economic, regulatory, and political uncertainties and can be extremely volatile. Foreign exchange rates also can be extremely volatile. Prepayment. The ability of an issuer of a debt security to repay principal prior to a security's maturity can cause greater price volatility if interest rates change. Issuer-Specific Changes. The value of an individual security or particular type of security can be more volatile than, and can perform differently from, the market as a whole. Changes in the financial condition of an issuer or counterparty (e.g., broker-dealer or other borrower in a securities lending transaction) can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's value or result in delays in recovering securities and/or capital from a counterparty. A decline in the credit quality of an issuer or a provider of credit support or a maturity-shortening structure for a security can cause the price of a security to decrease. Correlation to Index. The performance of an underlying index fund and its index may vary somewhat due to factors such as fees and expenses of the underlying fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from the index. Errors in the construction or calculation of the index may occur from time to time and may not be identified and corrected for some period of time, which may have an adverse impact on an underlying fund and its shareholders. Passive Management Risk. Some of the underlying funds in which the fund invests are managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of an underlying fund's index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the performance of these underlying funds could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers. An underlying index fund may be concentrated to approximately the same extent that its index concentrates in the securities of issuers in a particular industry or group of industries. Leverage Risk. Leverage can increase market exposure, magnify investment risks, and cause losses to be realized more quickly. An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You could lose money by investing in the fund.
Risk Lose Money [Text]	rr_RiskLoseMoney	You could lose money by investing in the fund.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	Performance history will be available for the fund after the fund has been in operation for one calendar year.
NF_05.31 Fidelity Sustainable Multi-Asset Fund AMCIZ PRO -01 | Fidelity Sustainable Multi-Asset Fund | Fidelity Advisor Sustainable Multi-Asset Fund: Class A
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) on purchases (as a % of offering price)	rr_MaximumCumulativeSalesChargeOverOfferingPrice	5.75%
Maximum contingent deferred sales charge (as a % of the lesser of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none	[1]
Management fee	rr_ManagementFeesOverAssets	0.10%
Distribution and/or Service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	none	[2]
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.37%	[2]
Total annual operating expenses	rr_ExpensesOverAssets	0.72%
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	0.05%	[3]
Total annual operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	0.67%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	Class A and Class M purchases of $1 million or more will not be subject to a front-end sales charge. Such Class A and Class M purchases may be subject, upon redemption, to a contingent deferred sales charge (CDSC) of 1.00% or 0.25%, respectively.
1 year	rr_ExpenseExampleYear01	$ 640
3 years	rr_ExpenseExampleYear03	782
1 Year	rr_ExpenseExampleNoRedemptionYear01	640
3 Years	rr_ExpenseExampleNoRedemptionYear03	$ 782
NF_05.31 Fidelity Sustainable Multi-Asset Fund AMCIZ PRO -01 | Fidelity Sustainable Multi-Asset Fund | Fidelity Advisor Sustainable Multi-Asset Fund: Class M
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) on purchases (as a % of offering price)	rr_MaximumCumulativeSalesChargeOverOfferingPrice	3.50%
Maximum contingent deferred sales charge (as a % of the lesser of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none	[1]
Management fee	rr_ManagementFeesOverAssets	0.10%
Distribution and/or Service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other expenses	rr_OtherExpensesOverAssets	none	[2]
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.37%	[2]
Total annual operating expenses	rr_ExpensesOverAssets	0.97%
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	0.05%	[3]
Total annual operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	0.92%
1 year	rr_ExpenseExampleYear01	$ 441
3 years	rr_ExpenseExampleYear03	638
1 Year	rr_ExpenseExampleNoRedemptionYear01	441
3 Years	rr_ExpenseExampleNoRedemptionYear03	$ 638
NF_05.31 Fidelity Sustainable Multi-Asset Fund AMCIZ PRO -01 | Fidelity Sustainable Multi-Asset Fund | Fidelity Advisor Sustainable Multi-Asset Fund: Class C
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) on purchases (as a % of offering price)	rr_MaximumCumulativeSalesChargeOverOfferingPrice	none
Maximum contingent deferred sales charge (as a % of the lesser of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[4]
Management fee	rr_ManagementFeesOverAssets	0.10%
Distribution and/or Service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	none	[2]
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.37%	[2]
Total annual operating expenses	rr_ExpensesOverAssets	1.47%
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	0.05%	[3]
Total annual operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	1.42%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	On Class C shares redeemed less than one year after purchase.
1 year	rr_ExpenseExampleYear01	$ 145
3 years	rr_ExpenseExampleYear03	455
1 Year	rr_ExpenseExampleNoRedemptionYear01	245
3 Years	rr_ExpenseExampleNoRedemptionYear03	$ 455
NF_05.31 Fidelity Sustainable Multi-Asset Fund AMCIZ PRO -01 | Fidelity Sustainable Multi-Asset Fund | Fidelity Advisor Sustainable Multi-Asset Fund: Class I
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) on purchases (as a % of offering price)	rr_MaximumCumulativeSalesChargeOverOfferingPrice	none
Maximum contingent deferred sales charge (as a % of the lesser of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Management fee	rr_ManagementFeesOverAssets	0.10%
Distribution and/or Service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	none	[2]
Acquired fund fees and expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.37%	[2]
Total annual operating expenses	rr_ExpensesOverAssets	0.47%
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	0.05%	[3]
Total annual operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	0.42%
1 year	rr_ExpenseExampleYear01	$ 43
3 years	rr_ExpenseExampleYear03	140
1 Year	rr_ExpenseExampleNoRedemptionYear01	43
3 Years	rr_ExpenseExampleNoRedemptionYear03	$ 140

[1] ^(a)Class A and Class M purchases of $1 million or more will not be subject to a front-end sales charge. Such Class A and Class M purchases may be subject, upon redemption, to a contingent deferred sales charge (CDSC) of 1.00% or 0.25%, respectively.

[2] ^(a)Based on estimated amounts for the current fiscal year.

[3] ^(b)Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse Class A, Class M, Class C, and Class I of the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, proxy and shareholder meeting expenses, extraordinary expenses, and acquired fund fees and expenses (including fees and expenses associated with a wholly owned subsidiary), if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of their respective average net assets, exceed 0.30%, 0.55%, 1.05%, and 0.05% (the Expense Caps). If at any time during the current fiscal year expenses for Class A, Class M, Class C, and Class I of the fund fall below the Expense Caps, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Caps. These arrangements will remain in effect through January 31, 2024 . FMR may not terminate these arrangements before the expiration date without the approval of the Board of Trustees and may extend them in its discretion after that date.

[4] ^(b)On Class C shares redeemed less than one year after purchase.