v3.26.1
Shareholder Report, Average Annual Return (Details)
 12 Months Ended 60 Months Ended 120 Months Ended
Jun. 30, 2026
Jun. 30, 2026
Jun. 30, 2026
C000100250 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Class K Shares    
Average Annual Return, Percent 6.41% 0.69% 1.96%
C000038033 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor C Shares (with sales charge)    
Average Annual Return, Percent 4.31% (0.38%) 1.05%
C000006118 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor A Shares (with sales charge)    
Average Annual Return, Percent 1.59% (0.48%) 1.22%
C000100249 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Service Shares    
Average Annual Return, Percent 6.10% 0.39% 1.66%
C000006121 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Institutional Shares    
Average Annual Return, Percent 6.36% 0.64% 1.91%
C000006125 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Institutional Shares    
Average Annual Return, Percent 4.36% 2.19% 1.64%
C000038034 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor A Shares (with sales charge)    
Average Annual Return, Percent 1.09% 1.33% 1.10%
C000006122 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor A1 Shares    
Average Annual Return, Percent 4.25% 2.09% 1.54%
C000006124 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor C Shares (with sales charge)    
Average Annual Return, Percent 2.35% 1.16% 0.78%
C000038035 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Class K Shares    
Average Annual Return, Percent 4.41% 2.25% 1.69%
Without Sales Load [Member] | C000038033 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor C Shares    
Average Annual Return, Percent 5.31% (0.38%) 1.05%
Without Sales Load [Member] | C000006118 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor A Shares    
Average Annual Return, Percent 6.10% 0.39% 1.66%
Without Sales Load [Member] | C000038034 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor A Shares    
Average Annual Return, Percent 4.21% 1.95% 1.41%
Without Sales Load [Member] | C000006124 [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Investor C Shares    
Average Annual Return, Percent 3.35% 1.16% 0.78%
Bloomberg Municipal Bond Index [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Bloomberg Municipal Bond Index    
Average Annual Return, Percent 7.03% 1.05% 2.15%
Bloomberg Municipal 1 5 Year Index [Member]      
Average Annual Return [Line Items]      
Line Graph and Table Measure Name Bloomberg Municipal 1-5 Year Index    
Average Annual Return, Percent 3.32% 1.55% 1.66%