v3.26.3
Average Annual Total Returns
 12 Months Ended 60 Months Ended 107 Months Ended 120 Months Ended 164 Months Ended 209 Months Ended 297 Months Ended 298 Months Ended 375 Months Ended
Sep. 30, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
AMERICAN HIGH-INCOME MUNICIPAL BOND FUND (Class A, Class C, Class F-1, Class F-2, Class F-3) | Class A                    
Prospectus [Line Items]                    
Average Annual Return, Percent   0.40% 1.37%   3.13%         4.86%
Performance Inception Date Sep. 26, 1994                  
AMERICAN HIGH-INCOME MUNICIPAL BOND FUND (Class A, Class C, Class F-1, Class F-2, Class F-3) | Class C                    
Prospectus [Line Items]                    
Average Annual Return, Percent   2.57% 1.41%   2.93%       4.15%  
Performance Inception Date Mar. 15, 2001                  
AMERICAN HIGH-INCOME MUNICIPAL BOND FUND (Class A, Class C, Class F-1, Class F-2, Class F-3) | Class F-1                    
Prospectus [Line Items]                    
Average Annual Return, Percent   4.28% 2.12%   3.49%     4.34%    
Performance Inception Date Mar. 19, 2001                  
AMERICAN HIGH-INCOME MUNICIPAL BOND FUND (Class A, Class C, Class F-1, Class F-2, Class F-3) | Class F-2                    
Prospectus [Line Items]                    
Average Annual Return, Percent   4.56% 2.39%   3.76%   4.77%      
Performance Inception Date Aug. 12, 2008                  
AMERICAN HIGH-INCOME MUNICIPAL BOND FUND (Class A, Class C, Class F-1, Class F-2, Class F-3) | Class F-2 | After Taxes on Distributions                    
Prospectus [Line Items]                    
Average Annual Return, Percent   4.56% 2.34%   3.73%          
AMERICAN HIGH-INCOME MUNICIPAL BOND FUND (Class A, Class C, Class F-1, Class F-2, Class F-3) | Class F-2 | After Taxes on Distributions and Sales                    
Prospectus [Line Items]                    
Average Annual Return, Percent   4.45% 2.67%   3.77%          
AMERICAN HIGH-INCOME MUNICIPAL BOND FUND (Class A, Class C, Class F-1, Class F-2, Class F-3) | Class F-3                    
Prospectus [Line Items]                    
Average Annual Return, Percent   4.67% 2.50% 4.07%            
Performance Inception Date Jan. 27, 2017                  
AMERICAN HIGH-INCOME MUNICIPAL BOND FUND (Class A, Class C, Class F-1, Class F-2, Class F-3) | Bloomberg Municipal Bond Index (reflects no deductions for sales charges, account fees, expenses or U.S. federal income taxes)                    
Prospectus [Line Items]                    
Average Annual Return, Percent   4.25% 0.80%   2.34%   3.52%      
AMERICAN HIGH-INCOME MUNICIPAL BOND FUND (Class R6) | Class R-6                    
Prospectus [Line Items]                    
Average Annual Return, Percent   4.66% 2.50%   3.87% 4.44%        
Performance Inception Date May 11, 2012                  
AMERICAN HIGH-INCOME MUNICIPAL BOND FUND (Class R6) | Class R-6 | After Taxes on Distributions                    
Prospectus [Line Items]                    
Average Annual Return, Percent   4.66% 2.45%   3.84%          
AMERICAN HIGH-INCOME MUNICIPAL BOND FUND (Class R6) | Class R-6 | After Taxes on Distributions and Sales                    
Prospectus [Line Items]                    
Average Annual Return, Percent   4.56% 2.77%   3.89%          
AMERICAN HIGH-INCOME MUNICIPAL BOND FUND (Class R6) | Bloomberg Municipal Bond Index (reflects no deductions for sales charges, account fees, expenses or U.S. federal income taxes)                    
Prospectus [Line Items]                    
Average Annual Return, Percent   4.25% 0.80%   2.34% 2.63%