v3.26.1
Average Annual Total Returns - Natixis Funds Trust I
 12 Months Ended 60 Months Ended 104 Months Ended 117 Months Ended 120 Months Ended
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Mirova Global Megatrends Fund | MSCI World Index (Net)          
Prospectus [Line Items]          
Average Annual Return, Percent 21.09% 12.15% 12.15% 12.49%  
Mirova Global Megatrends Fund | Class A          
Prospectus [Line Items]          
Average Annual Return, Percent 8.40% 5.72%   11.11%  
Mirova Global Megatrends Fund | Class C          
Prospectus [Line Items]          
Average Annual Return, Percent 13.17% 6.17%   11.10%  
Mirova Global Megatrends Fund | Class N          
Prospectus [Line Items]          
Average Annual Return, Percent 15.38% 7.30% 12.13%    
Mirova Global Megatrends Fund | Class Y          
Prospectus [Line Items]          
Average Annual Return, Percent 15.32% 7.24%   12.07%  
Mirova Global Megatrends Fund | Class Y | After Taxes on Distributions          
Prospectus [Line Items]          
Average Annual Return, Percent 14.06% 6.04%   11.20%  
Mirova Global Megatrends Fund | Class Y | After Taxes on Distributions and Sales          
Prospectus [Line Items]          
Average Annual Return, Percent 9.86% 5.49%   9.86%  
Vaughan Nelson Small Cap Fund | Russell 3000® Index          
Prospectus [Line Items]          
Average Annual Return, Percent 17.15% 13.15% 14.09%   14.29%
Vaughan Nelson Small Cap Fund | Russell 2000 Value Index          
Prospectus [Line Items]          
Average Annual Return, Percent 12.59% 8.88% 7.18%   9.27%
Vaughan Nelson Small Cap Fund | Class A          
Prospectus [Line Items]          
Average Annual Return, Percent 5.45% 10.04%     9.08%
Vaughan Nelson Small Cap Fund | Class C          
Prospectus [Line Items]          
Average Annual Return, Percent 10.17% 10.53%     9.06%
Vaughan Nelson Small Cap Fund | Class N          
Prospectus [Line Items]          
Average Annual Return, Percent 12.22% 11.68% 9.39%    
Vaughan Nelson Small Cap Fund | Class Y          
Prospectus [Line Items]          
Average Annual Return, Percent 12.16% 11.62%     10.00%
Vaughan Nelson Small Cap Fund | Class Y | After Taxes on Distributions          
Prospectus [Line Items]          
Average Annual Return, Percent 10.77% 9.54%     7.83%
Vaughan Nelson Small Cap Fund | Class Y | After Taxes on Distributions and Sales          
Prospectus [Line Items]          
Average Annual Return, Percent 8.24% 8.51%     7.33%
Natixis Oakmark International Fund | MSCI World ex USA Index (Net)          
Prospectus [Line Items]          
Average Annual Return, Percent 31.85% 9.46% 8.42%   8.55%
Natixis Oakmark International Fund | Class A          
Prospectus [Line Items]          
Average Annual Return, Percent 25.00% 5.22%     5.90%
Natixis Oakmark International Fund | Class A | After Taxes on Distributions          
Prospectus [Line Items]          
Average Annual Return, Percent 24.06% 4.79%     5.53%
Natixis Oakmark International Fund | Class A | After Taxes on Distributions and Sales          
Prospectus [Line Items]          
Average Annual Return, Percent 15.40% 4.10%     4.80%
Natixis Oakmark International Fund | Class C          
Prospectus [Line Items]          
Average Annual Return, Percent 30.66% 5.67%     5.89%
Natixis Oakmark International Fund | Class N          
Prospectus [Line Items]          
Average Annual Return, Percent 32.91% 6.77% 5.21%    
Natixis Oakmark International Fund | Class Y          
Prospectus [Line Items]          
Average Annual Return, Percent 32.94% 6.73%     6.76%
Natixis U.S. Equity Opportunities Fund | S&P 500® Index          
Prospectus [Line Items]          
Average Annual Return, Percent 17.88% 14.42% 14.77%   14.82%
Natixis U.S. Equity Opportunities Fund | Russell 1000® Index          
Prospectus [Line Items]          
Average Annual Return, Percent 17.37% 13.59% 14.49%   14.59%
Natixis U.S. Equity Opportunities Fund | Class A          
Prospectus [Line Items]          
Average Annual Return, Percent 10.57% 13.00%     14.56%
Natixis U.S. Equity Opportunities Fund | Class C          
Prospectus [Line Items]          
Average Annual Return, Percent 15.47% 13.49%     14.55%
Natixis U.S. Equity Opportunities Fund | Class N          
Prospectus [Line Items]          
Average Annual Return, Percent 17.68% 14.70% 15.57%    
Natixis U.S. Equity Opportunities Fund | Class Y          
Prospectus [Line Items]          
Average Annual Return, Percent 17.62% 14.63%     15.53%
Natixis U.S. Equity Opportunities Fund | Class Y | After Taxes on Distributions          
Prospectus [Line Items]          
Average Annual Return, Percent 16.31% 12.61%     13.58%
Natixis U.S. Equity Opportunities Fund | Class Y | After Taxes on Distributions and Sales          
Prospectus [Line Items]          
Average Annual Return, Percent 11.24% 11.17%     12.38%