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;">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)

Class Name	Cost of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Admin Class	$54	1.09%

Expenses Paid, Amount

$ 54

Expense Ratio, Percent

1.09%

AssetsNet

$ 4,356,767,123

Holdings Count | Holding

611

Advisory Fees Paid, Amount

$ 11,111,452

InvestmentCompanyPortfolioTurnover

33.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Total Net Assets	$4,356,767,123
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)	611
Portfolio Turnover Rate	33%
Total Advisory Fees Paid	$11,111,452

Holdings [Text Block]

Industry Summary

Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	30.3%
Short-Term Investments	3.2%
Pharmaceuticals	3.0%
ABS Car Loan	3.2%
Metals & Mining	3.2%
Life Insurance	3.3%
ABS Home Equity	4.2%
Collateralized Loan Obligations	4.3%
Banking	4.5%
Sovereigns	4.6%
ABS Other	5.0%
Technology	5.0%
Finance Companies	5.1%
Cable Satellite	7.3%
Treasuries	13.8%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including forward foreign currency and futures contracts)

Material Fund Change [Text Block]

Material Fund Changes

Effective July 1, 2024, 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.

Expenses:The expense limit as a percentage of average daily net assets was reduced to 1.15% from 1.16%.

Material Fund Change Expenses [Text Block]

Expenses:The expense limit as a percentage of average daily net assets was reduced to 1.15% from 1.16%.

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;">im.natixis.com/funddocuments</span>

C000125493

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Bond 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 Bond Fund for the period of January 1, 2024 to June 30, 2024.

Shareholder Report Annual or Semi-Annual

Semi-annual Shareholder Report

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)

Class Name	Cost of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Class N	$31	0.61%

Expenses Paid, Amount

$ 31

Expense Ratio, Percent

0.61%

AssetsNet

$ 4,356,767,123

Holdings Count | Holding

611

Advisory Fees Paid, Amount

$ 11,111,452

InvestmentCompanyPortfolioTurnover

33.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Total Net Assets	$4,356,767,123
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)	611
Portfolio Turnover Rate	33%
Total Advisory Fees Paid	$11,111,452

Holdings [Text Block]

Industry Summary

Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	30.3%
Short-Term Investments	3.2%
Pharmaceuticals	3.0%
ABS Car Loan	3.2%
Metals & Mining	3.2%
Life Insurance	3.3%
ABS Home Equity	4.2%
Collateralized Loan Obligations	4.3%
Banking	4.5%
Sovereigns	4.6%
ABS Other	5.0%
Technology	5.0%
Finance Companies	5.1%
Cable Satellite	7.3%
Treasuries	13.8%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including forward foreign currency and futures contracts)

Material Fund Change [Text Block]

Material Fund Changes

Expenses:The expense limit as a percentage of average daily net assets was reduced to 0.60% from 0.61%.

Material Fund Change Expenses [Text Block]

Expenses:The expense limit as a percentage of average daily net assets was reduced to 0.60% from 0.61%.

Summary of Change Legend [Text Block]

Updated Prospectus Phone Number

800-225-5478

Updated Prospectus Web Address

C000018122

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Bond Fund

Class Name

Institutional Class

Trading Symbol

LSBDX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Bond Fund for the period of January 1, 2024 to June 30, 2024.

Shareholder Report Annual or Semi-Annual

Semi-annual Shareholder Report

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)

Class Name	Cost of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Institutional Class	$33	0.66%

Expenses Paid, Amount

$ 33

Expense Ratio, Percent

0.66%

AssetsNet

$ 4,356,767,123

Holdings Count | Holding

611

Advisory Fees Paid, Amount

$ 11,111,452

InvestmentCompanyPortfolioTurnover

33.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Total Net Assets	$4,356,767,123
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)	611
Portfolio Turnover Rate	33%
Total Advisory Fees Paid	$11,111,452

Holdings [Text Block]

Industry Summary

Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	30.3%
Short-Term Investments	3.2%
Pharmaceuticals	3.0%
ABS Car Loan	3.2%
Metals & Mining	3.2%
Life Insurance	3.3%
ABS Home Equity	4.2%
Collateralized Loan Obligations	4.3%
Banking	4.5%
Sovereigns	4.6%
ABS Other	5.0%
Technology	5.0%
Finance Companies	5.1%
Cable Satellite	7.3%
Treasuries	13.8%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including forward foreign currency and futures contracts)

Material Fund Change [Text Block]

Material Fund Changes

Expenses:The expense limit as a percentage of average daily net assets was reduced to 0.65% from 0.66%.

Material Fund Change Expenses [Text Block]

Expenses:The expense limit as a percentage of average daily net assets was reduced to 0.65% from 0.66%.

Summary of Change Legend [Text Block]

Updated Prospectus Phone Number

800-225-5478

Updated Prospectus Web Address

C000018123

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Bond 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 Bond Fund for the period of January 1, 2024 to June 30, 2024.

Shareholder Report Annual or Semi-Annual

Semi-annual Shareholder Report

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)

Class Name	Cost of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Retail Class	$45	0.91%

Expenses Paid, Amount

$ 45

Expense Ratio, Percent

0.91%

AssetsNet

$ 4,356,767,123

Holdings Count | Holding

611

Advisory Fees Paid, Amount

$ 11,111,452

InvestmentCompanyPortfolioTurnover

33.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Total Net Assets	$4,356,767,123
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)	611
Portfolio Turnover Rate	33%
Total Advisory Fees Paid	$11,111,452

Holdings [Text Block]

Industry Summary

Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	30.3%
Short-Term Investments	3.2%
Pharmaceuticals	3.0%
ABS Car Loan	3.2%
Metals & Mining	3.2%
Life Insurance	3.3%
ABS Home Equity	4.2%
Collateralized Loan Obligations	4.3%
Banking	4.5%
Sovereigns	4.6%
ABS Other	5.0%
Technology	5.0%
Finance Companies	5.1%
Cable Satellite	7.3%
Treasuries	13.8%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including forward foreign currency and futures contracts)

Material Fund Change [Text Block]

Material Fund Changes

Expenses:The expense limit as a percentage of average daily net assets was reduced to 0.90% from 0.91%.

Material Fund Change Expenses [Text Block]

Expenses:The expense limit as a percentage of average daily net assets was reduced to 0.90% from 0.91%.

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, 2024 to June 30, 2024.

Shareholder Report Annual or Semi-Annual

Semi-annual Shareholder Report

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)

Class Name	Cost of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Institutional Class	$26	0.53%

Expenses Paid, Amount

$ 26

Expense Ratio, Percent

0.53%

AssetsNet

$ 206,243,272

Holdings Count | Holding

646

Advisory Fees Paid, Amount

$ 353,027

InvestmentCompanyPortfolioTurnover

19.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Total Net Assets	$206,243,272
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)	646
Portfolio Turnover Rate	19%
Total Advisory Fees Paid	$353,027

Holdings [Text Block]

Industry Summary

Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	32.8%
Short-Term Investments	4.0%
Metals & Mining	3.0%
Collateralized Loan Obligations	3.2%
Midstream	3.3%
Sovereigns	3.5%
Finance Companies	4.0%
ABS Home Equity	4.5%
ABS Other	4.5%
ABS Car Loan	5.0%
Technology	7.1%
Banking	9.2%
Treasuries	15.9%

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

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Updated Prospectus Phone Number

800-225-5478

Updated Prospectus Web Address