Shareholder Report, Average Annual Return (Details)	12 Months Ended		60 Months Ended	120 Months Ended
	May 31, 2025		May 31, 2025	May 31, 2025
C000001378 [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	with Maximum Sales Charge - 4.50%
Average Annual Return, Percent	(3.69%)		(0.89%)	0.95%
C000001376 [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	with Maximum Deferred Sales Charge - 1.00%
Average Annual Return, Percent	(0.91%)	[1]	(0.73%)	0.65%
C000073387 [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Class I
Average Annual Return, Percent	1.10%		0.27%	1.67%
C000130450 [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Class Y
Average Annual Return, Percent	1.17%		0.21%	1.65%
C000000023 [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Class Z
Average Annual Return, Percent	1.07%		0.25%	1.64%
Without Sales Load [Member] | C000001378 [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	without Sales Charge
Average Annual Return, Percent	0.86%		0.03%	1.42%
Without Sales Load [Member] | C000001376 [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	without Deferred Sales Charge
Average Annual Return, Percent	0.08%		(0.73%)	0.65%
Bloomberg U S Municipal Bond Index [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Bloomberg U.S. Municipal Bond Index
Average Annual Return, Percent	2.03%		0.55%	2.13%

[1] The maximum contingent deferred sales charge for Class C shares is 1.00% for shares redeemed within one year of the date purchased.