S 000000330 Summary1 [Member] Prospectus Summary Prospectus Summary S 000000330 [Member] BNY Mellon AMT-Free Municipal Bond Fund BNY Mellon AMT-Free Municipal Bond Fund C 000000815 [Member] A A C 000000817 [Member] C C C 000073398 [Member] I I C 000130452 [Member] Y Y C 000000818 [Member] Z Z cik0000878092_PrincipalRisks2Member [Member] Principal Risks Principal Risks cik0000878092_Municipalsecuritiesrisk2Member [Member] · Municipal securities risk · Municipal securities risk cik0000878092_Interestraterisk2Member [Member] · Interest rate risk · Interest rate risk cik0000878092_Creditrisk2Member [Member] · Credit risk · Credit risk cik0000878092_Highyieldsecuritiesrisk2Member [Member] · High yield securities risk · High yield securities risk cik0000878092_Liquidityrisk2Member [Member] · Liquidity risk · Liquidity risk cik0000878092_Prepaymentrisk2Member [Member] · Prepayment risk · Prepayment risk cik0000878092_Valuationrisk2Member [Member] · Valuation risk · Valuation risk cik0000878092_Marketrisk2Member [Member] · Market risk · Market risk cik0000878092_Managementrisk2Member [Member] · Management risk · Management risk cik0000878092_BloombergUSMunicipalBondIndexreflectsnodeductionsforfeesexpensesortaxes31Member [Member] Bloomberg U.S. Municipal Bond Indexreflects no deductions for fees, expenses or taxes Bloomberg U.S. Municipal Bond Indexreflects no deductions for fees, expenses or taxes S 000002850 Summary2 [Member] Prospectus Summary Prospectus Summary S 000002850 [Member] BNY Mellon High Yield Municipal Bond Fund BNY Mellon High Yield Municipal Bond Fund C 000046743 [Member] A A C 000046744 [Member] C C C 000073399 [Member] I I C 000130453 [Member] Y Y C 000007813 [Member] Z Z cik0000878092_Rule144Asecuritiesrisk2Member [Member] · Rule 144A securities risk · Rule 144A securities risk cik0000878092_BloombergUSMunicipalBondIndexreflectsnodeductionsforfeesexpensesortaxes32Member [Member] Bloomberg U.S. Municipal Bond Indexreflects no deductions for fees, expenses or taxes Bloomberg U.S. Municipal Bond Indexreflects no deductions for fees, expenses or taxes cik0000878092_BloombergMunicipalHighYieldIndexreflectsnodeductionsforfeesexpensesortaxes33Member [Member] Bloomberg Municipal High Yield Index*reflects no deductions for fees, expenses or taxes Bloomberg Municipal High Yield Index*reflects no deductions for fees, expenses or taxes Document [Axis] Series [Axis] Prospectus Prospectus [Table] Risk/Return: Performance Measure [Axis] Class [Axis] Before Taxes After Taxes on Distributions After Taxes on Distributions and Sales Risk [Axis] All Risks [Member] Risk Lose Money [Member] Risk Not Insured [Member] Risk Nondiversified Status [Member] Risk Not Insured Depository Institution [Member] Risk Money Market Fund Price Fluctuates [Member] Risk Money Market Fund May Impose Fees or Suspend Sales [Member] Risk Money Market Fund Sponsor May Not Provide Support [Member] Risk Money Market Fund May Not Preserve Dollar [Member] Risks [Table Text Block] Risks [Table Text Block]