v3.25.2
S000000289 [Member] Average Annual Total Returns
 12 Months Ended 60 Months Ended 102 Months Ended 120 Months Ended 131 Months Ended 307 Months Ended
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
S&P Municipal Bond Index (reflects no deduction for fees, expenses or taxes)            
Prospectus [Line Items]            
Average Annual Return, Percent [1] 1.90% 1.20%   2.34%    
S&P Municipal Yield Index (reflects no deduction for fees, expenses or taxes)            
Prospectus [Line Items]            
Average Annual Return, Percent [2] 5.63% 2.38%   4.08%    
Lipper High Yield Municipal Debt Funds Classification Average (reflects no deduction for taxes or sales loads)            
Prospectus [Line Items]            
Average Annual Return, Percent [3] 5.20% 1.30%   3.02%    
Class A            
Prospectus [Line Items]            
Average Annual Return, Percent 0.47% 0.21%   3.17%  
Performance Inception Date           Jun. 07, 1999
Class A | After Taxes on Distributions            
Prospectus [Line Items]            
Average Annual Return, Percent 0.28% 0.09%   3.09%  
Performance Inception Date           Jun. 07, 1999
Class A | After Taxes on Distributions and Sales            
Prospectus [Line Items]            
Average Annual Return, Percent 2.01% 1.15%   3.52%  
Performance Inception Date           Jun. 07, 1999
Class I            
Prospectus [Line Items]            
Average Annual Return, Percent 5.08% 1.29%   3.84%  
Performance Inception Date           Jun. 07, 1999
Class C            
Prospectus [Line Items]            
Average Annual Return, Percent 4.06% 0.26%   2.96%  
Performance Inception Date         Feb. 10, 2014  
Class R6            
Prospectus [Line Items]            
Average Annual Return, Percent 5.20% 1.32% 3.05%    
Performance Inception Date     Jun. 30, 2016      
Class R6 | S&P Municipal Bond Index (reflects no deduction for fees, expenses or taxes)            
Prospectus [Line Items]            
Average Annual Return, Percent [1]           1.86%
Class R6 | S&P Municipal Yield Index (reflects no deduction for fees, expenses or taxes)            
Prospectus [Line Items]            
Average Annual Return, Percent [2]           3.53%
Class R6 | Lipper High Yield Municipal Debt Funds Classification Average (reflects no deduction for taxes or sales loads)            
Prospectus [Line Items]            
Average Annual Return, Percent [3]           2.31%
[1]
An index designed to measure the performance of the tax-exempt U.S. municipal bond market.
[2]
An index that is structured so that 70% of the index consists of bonds that are either not rated or are rated below investment grade, 20% are rated BBB/Baa, and 10% are rated single A.
[3]
Represents the average annualized total return for all reporting funds in the Lipper High Yield Municipal Debt Funds Classification.