This semi-annual shareholder report contains important information about Loomis Sayles Income Fund for the period of January 1, 2026 to June 30, 2026.

Additional Information [Text Block]

You can find additional information (including tax information) about the Fund at im.natixis.com/funddocuments. You can also request this information by contacting us at (800) 225-5478 or by contacting your financial intermediary directly. This report describes changes to the Fund that occurred during the reporting period.

Material Fund Change Notice [Text Block]

This report describes changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

(800) 225-5478

Additional Information Website

<span style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 12px; font-weight: 400; grid-area: auto; line-height: 18px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: preserve-breaks;">im.natixis.com/funddocuments</span>

Expenses [Text Block]

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Table Summary
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment^{Footnote Reference†}
Institutional Class	$32	0.64%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 32

Expense Ratio, Percent

0.64%

Material Change Date

Jun. 30, 2026

AssetsNet

$ 4,314,063,952

Holdings Count | Holding

753

Advisory Fees Paid, Amount

$ 10,482,882

InvestmentCompanyPortfolioTurnover

38.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Total Net Assets$4,314,063,952
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)753
Portfolio Turnover Rate38%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)$10,482,882

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	43.8%
Short-Term Investments	3.7%
Finance Companies	3.3%
Life Insurance	3.4%
Sovereigns	3.6%
Equity-Linked Notes	4.0%
Banking	4.6%
Cable Satellite	4.9%
ABS Other	5.6%
Technology	7.9%
Treasuries	15.2%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including open written options and futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	2.8
US Treasury	11.2
Not rated^{Footnote Reference^}	18.4
CC	0.3
CCC	1.2
B	6.5
BB	13.5
BBB	37.2
A	8.0
AA	1.4
AAA	1.1

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.

Material Fund Change [Text Block]

Material Fund Changes

For the six months ended June 30, 2026, the Fund had the following material changes, which were reported in a supplement to the Fund's prospectus. For more information, you may review the Fund's prospectus at im.natixis.com/funddocuments or upon request at (800) 225-5478 or through your financial intermediary.

Fees: Effective July 1, 2026, the advisory fee rate as a percentage of average daily net assets will be 0.59% on the first $3 billion of assets, and 0.48% thereafter.

Material Fund Change Expenses [Text Block]

Fees: Effective July 1, 2026, the advisory fee rate as a percentage of average daily net assets will be 0.59% on the first $3 billion of assets, and 0.48% thereafter.

Summary of Change Legend [Text Block]

Updated Prospectus Phone Number

(800) 225-5478

Updated Prospectus Web Address

<span style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 10.6667px; font-weight: 400; grid-area: auto; line-height: 16px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: preserve-breaks;">im.natixis.com/funddocuments</span>

C000018123

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Income Fund

Class Name

Retail Class

Trading Symbol

LSBRX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Income Fund for the period of January 1, 2026 to June 30, 2026.

Additional Information [Text Block]

Material Fund Change Notice [Text Block]

This report describes changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

(800) 225-5478

Additional Information Website

Expenses [Text Block]

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Table Summary
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment^{Footnote Reference†}
Retail Class	$44	0.89%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 44

Expense Ratio, Percent

0.89%

Material Change Date

Jun. 30, 2026

AssetsNet

$ 4,314,063,952

Holdings Count | Holding

753

Advisory Fees Paid, Amount

$ 10,482,882

InvestmentCompanyPortfolioTurnover

38.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Total Net Assets$4,314,063,952
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)753
Portfolio Turnover Rate38%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)$10,482,882

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	43.8%
Short-Term Investments	3.7%
Finance Companies	3.3%
Life Insurance	3.4%
Sovereigns	3.6%
Equity-Linked Notes	4.0%
Banking	4.6%
Cable Satellite	4.9%
ABS Other	5.6%
Technology	7.9%
Treasuries	15.2%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including open written options and futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	2.8
US Treasury	11.2
Not rated^{Footnote Reference^}	18.4
CC	0.3
CCC	1.2
B	6.5
BB	13.5
BBB	37.2
A	8.0
AA	1.4
AAA	1.1

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

Fees: Effective July 1, 2026, the advisory fee rate as a percentage of average daily net assets will be 0.59% on the first $3 billion of assets, and 0.48% thereafter.

Material Fund Change Expenses [Text Block]

Fees: Effective July 1, 2026, the advisory fee rate as a percentage of average daily net assets will be 0.59% on the first $3 billion of assets, and 0.48% thereafter.

Summary of Change Legend [Text Block]

Updated Prospectus Phone Number

(800) 225-5478

Updated Prospectus Web Address

C000018124

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Income Fund

Class Name

Admin Class

Trading Symbol

LBFAX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Income Fund for the period of January 1, 2026 to June 30, 2026.

Additional Information [Text Block]

Material Fund Change Notice [Text Block]

This report describes changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

(800) 225-5478

Additional Information Website

Expenses [Text Block]

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Table Summary
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment^{Footnote Reference†}
Admin Class	$55	1.10%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 55

Expense Ratio, Percent

1.10%

Material Change Date

Jun. 30, 2026

AssetsNet

$ 4,314,063,952

Holdings Count | Holding

753

Advisory Fees Paid, Amount

$ 10,482,882

InvestmentCompanyPortfolioTurnover

38.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Total Net Assets$4,314,063,952
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)753
Portfolio Turnover Rate38%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)$10,482,882

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	43.8%
Short-Term Investments	3.7%
Finance Companies	3.3%
Life Insurance	3.4%
Sovereigns	3.6%
Equity-Linked Notes	4.0%
Banking	4.6%
Cable Satellite	4.9%
ABS Other	5.6%
Technology	7.9%
Treasuries	15.2%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including open written options and futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	2.8
US Treasury	11.2
Not rated^{Footnote Reference^}	18.4
CC	0.3
CCC	1.2
B	6.5
BB	13.5
BBB	37.2
A	8.0
AA	1.4
AAA	1.1

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

Fees: Effective July 1, 2026, the advisory fee rate as a percentage of average daily net assets will be 0.59% on the first $3 billion of assets, and 0.48% thereafter.

Material Fund Change Expenses [Text Block]

Fees: Effective July 1, 2026, the advisory fee rate as a percentage of average daily net assets will be 0.59% on the first $3 billion of assets, and 0.48% thereafter.

Summary of Change Legend [Text Block]

Updated Prospectus Phone Number

(800) 225-5478

Updated Prospectus Web Address

C000125493

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Income Fund

Class Name

Class N

Trading Symbol

LSBNX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Income Fund for the period of January 1, 2026 to June 30, 2026.

Additional Information [Text Block]

Material Fund Change Notice [Text Block]

This report describes changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

(800) 225-5478

Additional Information Website

Expenses [Text Block]

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Table Summary
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment^{Footnote Reference†}
Class N	$29	0.59%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 29

Expense Ratio, Percent

0.59%

Material Change Date

Jun. 30, 2026

AssetsNet

$ 4,314,063,952

Holdings Count | Holding

753

Advisory Fees Paid, Amount

$ 10,482,882

InvestmentCompanyPortfolioTurnover

38.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Total Net Assets$4,314,063,952
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)753
Portfolio Turnover Rate38%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)$10,482,882

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	43.8%
Short-Term Investments	3.7%
Finance Companies	3.3%
Life Insurance	3.4%
Sovereigns	3.6%
Equity-Linked Notes	4.0%
Banking	4.6%
Cable Satellite	4.9%
ABS Other	5.6%
Technology	7.9%
Treasuries	15.2%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including open written options and futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	2.8
US Treasury	11.2
Not rated^{Footnote Reference^}	18.4
CC	0.3
CCC	1.2
B	6.5
BB	13.5
BBB	37.2
A	8.0
AA	1.4
AAA	1.1

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

Fees: Effective July 1, 2026, the advisory fee rate as a percentage of average daily net assets will be 0.59% on the first $3 billion of assets, and 0.48% thereafter.

Material Fund Change Expenses [Text Block]

Fees: Effective July 1, 2026, the advisory fee rate as a percentage of average daily net assets will be 0.59% on the first $3 billion of assets, and 0.48% thereafter.

Summary of Change Legend [Text Block]

Updated Prospectus Phone Number

(800) 225-5478

Updated Prospectus Web Address

C000018133

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Investment Grade Fixed Income Fund

Class Name

Institutional Class

Trading Symbol

LSIGX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Investment Grade Fixed Income Fund for the period of January 1, 2026 to June 30, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 225-5478

Additional Information Website

Expenses [Text Block]

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Table Summary
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment^{Footnote Reference†}
Institutional Class	$26	0.53%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 26

Expense Ratio, Percent

0.53%

AssetsNet

$ 178,074,733

Holdings Count | Holding

649

Advisory Fees Paid, Amount

$ 293,519

InvestmentCompanyPortfolioTurnover

35.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Total Net Assets$178,074,733
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)649
Portfolio Turnover Rate35%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)$293,519

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	44.1%
Cable Satellite	3.0%
Midstream	3.0%
ABS Car Loan	4.8%
Banking	6.2%
Collateralized Loan Obligations	6.3%
Technology	8.0%
ABS Other	8.0%
Treasuries	16.6%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	1.6
US Treasury	14.0
Not rated^{Footnote Reference^}	20.1
CC	0.1
CCC	0.2
B	2.7
BB	5.6
BBB	41.5
A	9.3
AA	2.4
AAA	3.3

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Credit Quality^{Footnote Reference*}^{Footnote Reference†}