Shareholder Report, Average Annual Return (Details)

12 Months Ended

60 Months Ended

120 Months Ended

May 31, 2026

May 31, 2026

May 31, 2026

C000001376 [Member]

Average Annual Return [Line Items]

Line Graph and Table Measure Name

with Maximum Deferred Sales Charge - 1.00%

Average Annual Return, Percent

4.21%

^[1]

(0.59%)

0.59%

C000001378 [Member]

Average Annual Return [Line Items]

Line Graph and Table Measure Name

with Maximum Sales Charge - 4.50%

Average Annual Return, Percent

1.38%

(0.72%)

0.92%

C000000023 [Member]

Average Annual Return [Line Items]

Line Graph and Table Measure Name

Class Z

Average Annual Return, Percent

6.39%

0.41%

1.60%

C000130450 [Member]

Average Annual Return [Line Items]

Line Graph and Table Measure Name

Class Y

Average Annual Return, Percent

6.49%

0.39%

1.62%

C000073387 [Member]

Average Annual Return [Line Items]

Line Graph and Table Measure Name

Class I

Average Annual Return, Percent

6.43%

0.44%

1.63%

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

5.21%

(0.59%)

0.59%

Without Sales Load [Member] | C000001378 [Member]

Average Annual Return [Line Items]

Line Graph and Table Measure Name

without Sales Charge

Average Annual Return, Percent

6.18%

0.21%

1.39%

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

6.67%

0.92%

2.21%

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