Bloomberg U S Municipal Bond C000130450 Index [Member] Bloomberg U S Municipal Bond Index [Member] Medical [Member] Transportation Sector [Member] Education [Member] Airport [Member] Housing [Member] Nursing Homes [Member] Power [Member] Tobacco Settlement [Member] Development [Member] School District [Member] Water And Sewer [Member] General Obligation [Member] Net Other Assets and Liabilities [Member] C000001376 [Member] Class C C000001378 [Member] Class A C000000023 [Member] Class Z C000130450 [Member] Class Y C000073387 [Member] Class I Investment Type [Axis] Net Assets Investment Company Portfolio Turnover No Trading Symbol Flag