Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	LOOMIS SAYLES FUNDS II
Prospectus Date	rr_ProspectusDate	Feb. 01, 2013
Loomis Sayles Strategic Income Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Loomis Sayles Strategic Income Fund
Objective [Heading]	rr_ObjectiveHeading	Investment Goal
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund seeks high current income
Objective, Secondary [Text Block]	rr_ObjectiveSecondaryTextBlock	with a secondary objective of capital growth.
Expense [Heading]	rr_ExpenseHeading	Fund Fees & Expenses
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The following table describes the fees and expenses that you may pay if you buy and hold shares 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 $100,000 in the Natixis Fund Complex. More information about these and other discounts is available from your financial professional and in the section “How Sales Charges Are Calculated” on page 55 of the Prospectus and on page 110 in the section “Reduced Sales Charges” of the Statement of Additional Information (“SAI”).
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	January 31, 2014
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes for you if your Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During its most recently ended fiscal year, the Fund’s portfolio turnover rate was 30% the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	30.00%
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 $100,000 in the Natixis Fund Complex.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	100,000
Other Expenses, New Fund, Based on Estimates [Text]	rr_OtherExpensesNewFundBasedOnEstimates	Other expenses for Class N shares are estimated for the current fiscal year.
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example by, Year, Caption [Text]	rr_ExpenseExampleByYearCaption	If shares are redeemed:
Expense Example, No Redemption, By Year, Caption [Text]	rr_ExpenseExampleNoRedemptionByYearCaption	If shares are not redeemed:
Strategy [Heading]	rr_StrategyHeading	Investments, Risks and Performance Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal market conditions, the Fund will invest substantially all of its assets in income producing securities (including below investment-grade securities, or “junk bonds”) with a focus on U.S. corporate bonds, convertible securities, foreign debt instruments, including those in emerging markets and related foreign currency transactions, and U.S. government securities. Below investment-grade fixed-income securities are rated below investment-grade quality ( i.e. , none of the three major ratings agencies (Moody’s Investors Service, Inc. (“Moody’s”), Fitch Investors Services, Inc. (“Fitch”) or Standard and Poor’s Ratings Group (“S&P”)), have rated the securities in one of its top four rating categories) or, if the security is unrated, are determined by the Adviser to be of comparable quality. The Fund may invest up to 35% of its assets in preferred stocks and dividend-paying common stocks. The portfolio managers may shift the Fund’s assets among various types of income-producing securities based upon changing market conditions. The Adviser performs its own extensive credit analyses to determine the creditworthiness and potential for capital appreciation of a security. The Fund’s portfolio managers use a flexible approach to identify securities in the global marketplace with characteristics including discounted price compared to economic value, undervalued credit ratings with strong or improving credit profiles and yield premium relative to its benchmark (although not all of the securities selected will have these attributes). In deciding which securities to buy and sell, the Adviser will consider, among other things, the financial strength of the issuer, current interest rates, current valuations, the Adviser’s expectations regarding future changes in interest rates and comparisons of the level of risk associated with particular investments with the Adviser’s expectations concerning the potential return of those investments. In selecting investments for the Fund, the Adviser utilizes the skills of its in-house team of more than 30 research analysts to cover a broad universe of industries, companies and markets. The Fund’s portfolio managers take advantage of these extensive resources to identify securities that meet the Fund’s investment criteria. The Adviser seeks to buy bonds that offer a positive yield advantage over the market and, in its view, have room to increase in price. It may also invest to take advantage of what the portfolio managers believe are temporary disparities in the yield of different segments of the market for U.S. government securities. The Adviser provides the portfolio managers with maximum flexibility to find investment opportunities in a wide range of markets, both domestic and foreign. This flexible approach provides the Fund with access to a wide array of investment opportunities. The three key sectors that the portfolio managers focus upon are U.S. corporate issues (including convertible securities), foreign debt securities and U.S. government securities. The Fund’s portfolio managers maintain a core of the Fund’s investments in corporate bond issues and shift its assets among other income-producing securities as opportunities develop. The Fund generally seeks to maintain a high level of diversification as a form of risk management. In connection with its principal investment strategies, the Fund may also invest in securities issued pursuant to Rule 144 under the Securities Act of 1933 (“Rule 144A securities”), structured notes, zero-coupon bonds, pay-in-kind bonds, mortgage-related securities, stripped securities and futures, swaps (including credit default swaps) and foreign currency transactions for hedging and investment purposes. The Adviser may elect not to hedge currency risk, which may cause the Fund to incur losses that would not have been incurred had the risk been hedged. Except as provided above, the Fund is not limited in the percentage of its assets that it may invest in these instruments.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	The principal risks of investing in the Fund are summarized below. The Fund does not represent a complete investment program. You may lose money by investing in the Fund. Below Investment-Grade Fixed-Income Securities Risk: The Fund’s investments in below investment-grade fixed-income securities, also known as “junk bonds,” may be subject to greater risks than other fixed-income securities, including being subject to greater levels of interest rate risk, credit risk (including a greater risk of default) and liquidity risk. The ability of the issuer to make principal and interest payments is predominantly speculative for below investment-grade fixed-income securities. Credit Risk: Credit risk is the risk that the issuer or the guarantor of a fixed-income security, or the counterparty to a derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations. Currency Risk: Fluctuations in the exchange rates between different currencies may negatively affect an investment. The Fund may elect not to hedge currency risk, or may hedge such risk imperfectly, which may cause the Fund to incur losses that would not have been incurred had the risk been hedged. Derivatives Risk: Derivative instruments (such as those in which the Fund may invest) can be used to acquire or to transfer the risk and returns of a security or other asset without buying or selling the security or asset. Derivatives are subject to changes in the value of the underlying asset or indices on which such transactions are based. There is no guarantee that the use of derivatives will be effective or that suitable transactions will be available. Even a small investment in derivatives may give rise to leverage risk and can have a significant impact on the Fund’s exposure to securities markets values, interest rates or currency exchange rates. It is possible that the Fund’s liquid assets may be insufficient to support its obligations under its derivatives positions. The use of derivatives for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedging. The use of derivatives may cause the Fund to incur losses greater than those which would have occurred had derivatives not been used. The Fund’s use of derivatives such as forward currency contracts, structured notes, futures transactions and swap transactions involves other risks, such as the credit risk relating to the other party to a derivative contract (which is greater for forward currency contracts, swaps and other over-the-counter traded derivatives), the risk of difficulties in pricing and valuation, the risk that changes in the value of a derivative may not correlate perfectly with relevant assets, rates or indices, liquidity risk, allocation risk and the risk of losing more than the initial margin required to initiate derivatives positions. There is also the risk that the Fund may be unable to terminate or sell a derivatives position at an advantageous time or price. Moreover, a number of broker-dealers and other financial institutions have recently experienced extreme financial difficulty, sometimes resulting in bankruptcy of the institution. There can be no assurance that the Fund’s derivative counterparties will not experience similar financial difficulties, possibly resulting in losses to the Fund. Emerging Markets Risk: Investing in emerging markets companies, which may be smaller and have shorter operating histories than companies in developed markets, involves risks in addition to, and greater than, those generally associated with investing in companies in developed foreign markets. The extent of economic development, political stability, market depth, infrastructure, capitalization and regulatory oversight in emerging market economies is generally less than in more developed markets. Equity Securities Risk: The value of the Fund’s investments in equity securities could be subject to unpredictable declines in the value of individual securities and periods of below-average performance in individual securities or in the equity market as a whole. In the event an issuer is liquidated or declares bankruptcy, the claims of owners of the issuer’s bonds generally take precedence over the claims of those who own preferred stock or common stock. Fixed-Income Securities Risk: Fixed-income securities are subject to credit risk, interest rate risk and liquidity risk. You may lose money on your investment due to unpredictable drops in a security’s value or periods of below-average performance in a given security or in the securities market as a whole. Below investment-grade fixed-income securities may be subject to these risks (including the risk of default) to a greater extent than other fixed-income securities. In addition, an economic downturn or period of rising interest rates could adversely affect the market of these securities and reduce the Fund’s ability to sell them. Zero-coupon bonds may be subject to these risks to a greater extent than other fixed-income securities. Rule 144A securities and structured notes may be more illiquid than other fixed-income securities. Foreign Securities Risk: Investments in foreign securities may be subject to greater political, economic, environmental, credit and information risks. The Fund’s investments in foreign securities are also subject to foreign currency fluctuations. Foreign securities may be subject to higher volatility than U.S. securities, varying degrees of regulation and limited liquidity. Interest Rate Risk: Changes in interest rates may cause the value of the Fund’s investments to decrease. Generally, the value of fixed-income securities rises when prevailing interest rates fall and falls when interest rates rise. A prolonged period of low interest rates may cause the Fund to have a low or negative yield, potentially reducing the value of your investment. The value of zero-coupon bonds may be more sensitive to fluctuations in interest rates than other fixed income securities. Issuer Risk: The value of the Fund’s investments may decline for a number of reasons that directly relate to the issuer, such as management performance, financial leverage and reduced demand for the issuer’s goods and services. Leverage Risk: Use of derivative instruments may involve leverage. Leverage is the risk associated with securities or practices that multiply small index, market or asset price movements into larger changes in value. To the extent that the Fund uses a derivative for purposes other than as a hedge, or if the Fund hedges imperfectly, the Fund is directly exposed to the risks of that derivative and any loss generated by the derivative will not be offset by a gain. The use of leverage increases the impact of gains and losses on a fund’s returns, and may lead to significant losses if investments are not successful. Liquidity Risk: Liquidity risk exists when particular investments are difficult to purchase or sell, possibly preventing the Fund from selling these illiquid securities at an advantageous price or time. A lack of liquidity also may cause the value of investments to decline. Securities acquired in a private placement, such as Rule 144A securities, generally are subject to strict restrictions on resale and there may be no liquid secondary market or ready purchaser for such securities. Therefore, the Fund may be unable to dispose of such securities when it desires to do so, or at the most advantageous time or price. Illiquid investments also may be difficult to value. Management Risk: A strategy used by the Fund’s portfolio managers may fail to produce the intended result. Market Risk: The market value of a security will move up and down, sometimes rapidly and unpredictably, based upon a change in an issuer’s financial condition, as well as overall market and economic conditions. Mortgage-Related and Asset-Backed Securities Risk: In addition to the risks associated with investments in fixed-income securities generally (for example, credit, liquidity and valuation risk), mortgage-related and asset-backed securities are subject to the risks of the mortgages and assets underlying the securities as well as prepayment risk, the risk that the securities may be prepaid and result in the reinvestment of the prepaid amounts in securities with lower yields than the prepaid obligations. Conversely, there is a risk that an unexpected rise in interest rates will extend the life of a mortgage-related or asset-backed security beyond the expected prepayment time, typically reducing the security’s value. The Fund also may incur a loss when there is a prepayment of securities that were purchased at a premium. The Fund’s investments in other asset-backed securities are subject to risks similar to those associated with mortgage-related securities, as well as additional risks associated with the nature of the assets and the servicing of those assets.
Risk Lose Money [Text]	rr_RiskLoseMoney	You may lose money by investing in the Fund.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Risk/Return Bar Chart and Table
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year-to-year and by showing how the Fund’s average annual returns for the one-year, five-year and ten-year periods compare to those of two broad measures of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future. Updated performance information is available online at ngam.natixis.com and/or by calling the Fund toll-free at 800-225-5478. The chart does not reflect any sales charge that you may be required to pay when you buy or redeem the Fund’s shares. A sales charge will reduce your return.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year-to-year and by showing how the Fund’s average annual returns for the one-year, five-year and ten-year periods compare to those of two broad measures of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-225-5478
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	ngam.natixis.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund’s past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Total Returns for Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	The chart does not reflect any sales charge that you may be required to pay when you buy or redeem the Fund’s shares. A sales charge will reduce your return.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Highest Quarterly Return: Second Quarter 2009, 18.02% Lowest Quarterly Return: Third Quarter 2008, -13.38% Class B total returns in the table below do not reflect the automatic conversion of Class B shares to Class A shares after eight years.
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (for the periods ended December 31, 2012)
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Index performance reflects no deduction for fees, expenses, or taxes.
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	After-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	The after-tax returns are shown for only one class of the Fund. After-tax returns for the other classes of the Fund will vary.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The returns shown in the bar chart and table for the periods prior to September 15, 2003 reflect the results of the CDC Nvest Strategic Income Fund, whose assets and liabilities were reorganized into the Fund on September 12, 2003. Prior to the inception of Admin Class shares (February 1, 2010), performance is that of Class A shares, restated to reflect the higher net expenses of Admin Class shares. Because the Fund did not have Class N shares outstanding during the periods shown, performance is that of Class Y shares of the Fund. Class N shares would have had substantially similar returns because they would have been invested in the same portfolio of securities as Class Y shares and would only differ to the extent the classes did not have the same expenses. The Class N returns may be higher than the returns of Class Y shares because Class Y shares are subject to higher expenses. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts. The after-tax returns are shown for only one class of the Fund. After-tax returns for the other classes of the Fund will vary. Index performance reflects no deduction for fees, expenses, or taxes.
Loomis Sayles Strategic Income Fund | Class A
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	4.50%
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Redemption fees	rr_RedemptionFeeOverRedemption	none
Management fees	rr_ManagementFeesOverAssets	0.56%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.15%	[1],[2]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.96%
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	none	[3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	0.96%
1 year	rr_ExpenseExampleYear01	544
3 years	rr_ExpenseExampleYear03	742
5 years	rr_ExpenseExampleYear05	957
10 years	rr_ExpenseExampleYear10	1,575
2003	rr_AnnualReturn2003	34.84%
2004	rr_AnnualReturn2004	12.93%
2005	rr_AnnualReturn2005	3.74%
2006	rr_AnnualReturn2006	11.86%
2007	rr_AnnualReturn2007	7.26%
2008	rr_AnnualReturn2008	(23.15%)
2009	rr_AnnualReturn2009	39.30%
2010	rr_AnnualReturn2010	13.53%
2011	rr_AnnualReturn2011	3.35%
2012	rr_AnnualReturn2012	13.56%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Highest Quarterly Return:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	18.02%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Lowest Quarterly Return:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(13.38%)
Past 1 Year	rr_AverageAnnualReturnYear01	9.59%
Past 5 Years	rr_AverageAnnualReturnYear05	6.60%
Past 10 Years	rr_AverageAnnualReturnYear10	10.06%
Loomis Sayles Strategic Income Fund | Class B
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)	rr_MaximumDeferredSalesChargeOverOfferingPrice	5.00%
Redemption fees	rr_RedemptionFeeOverRedemption	none
Management fees	rr_ManagementFeesOverAssets	0.56%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.15%	[1],[2]
Total annual fund operating expenses	rr_ExpensesOverAssets	1.71%
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	none	[3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	1.71%
1 year	rr_ExpenseExampleYear01	674
3 years	rr_ExpenseExampleYear03	839
5 years	rr_ExpenseExampleYear05	1,128
10 years	rr_ExpenseExampleYear10	1,821
1 year	rr_ExpenseExampleNoRedemptionYear01	174
3 years	rr_ExpenseExampleNoRedemptionYear03	539
5 years	rr_ExpenseExampleNoRedemptionYear05	928
10 years	rr_ExpenseExampleNoRedemptionYear10	1,821
Past 1 Year	rr_AverageAnnualReturnYear01	7.75%
Past 5 Years	rr_AverageAnnualReturnYear05	6.23%
Past 10 Years	rr_AverageAnnualReturnYear10	9.62%
Loomis Sayles Strategic Income Fund | Class C
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)	rr_MaximumDeferredSalesChargeOverOfferingPrice	1.00%
Redemption fees	rr_RedemptionFeeOverRedemption	none
Management fees	rr_ManagementFeesOverAssets	0.56%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other expenses	rr_OtherExpensesOverAssets	0.15%	[1],[2]
Total annual fund operating expenses	rr_ExpensesOverAssets	1.71%
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	none	[3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	1.71%
1 year	rr_ExpenseExampleYear01	274
3 years	rr_ExpenseExampleYear03	539
5 years	rr_ExpenseExampleYear05	928
10 years	rr_ExpenseExampleYear10	2,019
1 year	rr_ExpenseExampleNoRedemptionYear01	174
3 years	rr_ExpenseExampleNoRedemptionYear03	539
5 years	rr_ExpenseExampleNoRedemptionYear05	928
10 years	rr_ExpenseExampleNoRedemptionYear10	2,019
Past 1 Year	rr_AverageAnnualReturnYear01	11.70%
Past 5 Years	rr_AverageAnnualReturnYear05	6.55%
Past 10 Years	rr_AverageAnnualReturnYear10	9.63%
Loomis Sayles Strategic Income Fund | Class N
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Redemption fees	rr_RedemptionFeeOverRedemption	none
Management fees	rr_ManagementFeesOverAssets	0.56%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.06%	[1],[2],[4]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.62%
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	none	[3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	0.62%
1 year	rr_ExpenseExampleYear01	63
3 years	rr_ExpenseExampleYear03	199
5 years	rr_ExpenseExampleYear05	346
10 years	rr_ExpenseExampleYear10	774
Past 1 Year	rr_AverageAnnualReturnYear01	13.93%
Past 5 Years	rr_AverageAnnualReturnYear05	7.63%
Past 10 Years	rr_AverageAnnualReturnYear10	10.74%
Loomis Sayles Strategic Income Fund | Class Y
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Redemption fees	rr_RedemptionFeeOverRedemption	none
Management fees	rr_ManagementFeesOverAssets	0.56%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.15%	[1],[2]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.71%
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	none	[3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	0.71%
1 year	rr_ExpenseExampleYear01	73
3 years	rr_ExpenseExampleYear03	227
5 years	rr_ExpenseExampleYear05	395
10 years	rr_ExpenseExampleYear10	883
Past 1 Year	rr_AverageAnnualReturnYear01	13.93%
Past 5 Years	rr_AverageAnnualReturnYear05	7.63%
Past 10 Years	rr_AverageAnnualReturnYear10	10.74%
Loomis Sayles Strategic Income Fund | Admin Class
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Redemption fees	rr_RedemptionFeeOverRedemption	none
Management fees	rr_ManagementFeesOverAssets	0.56%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.40%	[1],[2]
Total annual fund operating expenses	rr_ExpensesOverAssets	1.21%
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	none	[3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	1.21%
1 year	rr_ExpenseExampleYear01	123
3 years	rr_ExpenseExampleYear03	384
5 years	rr_ExpenseExampleYear05	665
10 years	rr_ExpenseExampleYear10	1,466
Past 1 Year	rr_AverageAnnualReturnYear01	13.33%
Past 5 Years	rr_AverageAnnualReturnYear05	7.06%
Past 10 Years	rr_AverageAnnualReturnYear10	10.13%
Loomis Sayles Strategic Income Fund | Return After Taxes on Distributions | Class A
Risk/Return:	rr_RiskReturnAbstract
Past 1 Year	rr_AverageAnnualReturnYear01	7.73%
Past 5 Years	rr_AverageAnnualReturnYear05	4.31%
Past 10 Years	rr_AverageAnnualReturnYear10	7.75%
Loomis Sayles Strategic Income Fund | Return After Taxes on Distributions & Sale of Fund Shares | Class A
Risk/Return:	rr_RiskReturnAbstract
Past 1 Year	rr_AverageAnnualReturnYear01	6.33%
Past 5 Years	rr_AverageAnnualReturnYear05	4.25%
Past 10 Years	rr_AverageAnnualReturnYear10	7.38%
Loomis Sayles Strategic Income Fund | Barclays U.S. Aggregate Bond Index
Risk/Return:	rr_RiskReturnAbstract
Past 1 Year	rr_AverageAnnualReturnYear01	4.21%
Past 5 Years	rr_AverageAnnualReturnYear05	5.95%
Past 10 Years	rr_AverageAnnualReturnYear10	5.18%
Loomis Sayles Strategic Income Fund | Barclays U.S. Universal Bond Index
Risk/Return:	rr_RiskReturnAbstract
Past 1 Year	rr_AverageAnnualReturnYear01	5.53%
Past 5 Years	rr_AverageAnnualReturnYear05	6.19%
Past 10 Years	rr_AverageAnnualReturnYear10	5.59%

[1] Other expenses include an administrative service fee of 0.25% for Admin Class shares.

[2] The expense information shown in the table above may differ from the expense information disclosed in the Fund's financial highlights table because the financial highlights table reflects the operating expenses of the Fund and does not include acquired fund fees and expenses (expenses indirectly borne by the Fund through investments in certain pooled investment vehicles).

[3] Loomis, Sayles & Company, L.P. ("Loomis Sayles" or the "Adviser") has given a binding contractual undertaking to the Fund to limit the amount of the Fund's total annual fund operating expenses to 1.25%, 2.00%, 2.00%, 0.95%, 1.00% and 1.50 % of the Fund's average daily net assets for Class A, B, C, N, Y and Admin Class shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through January 31, 2014 and may be terminated before then only with the consent of the Fund's Board of Trustees. The Adviser will be permitted to recover, on a class by class basis, management fees waived and/or expenses reimbursed to the extent that expenses in later periods fall below 1.25%, 2.00%, 2.00%, 0.95%, 1.00% and 1.50 % of the Fund's average daily net assets for Class A, B, C, N, Y and Admin Class shares, respectively. The Fund will not be obligated to repay any such waived/reimbursed fees and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.

[4] Other expenses for Class N shares are estimated for the current fiscal year.