Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	FEDERATED MUNICIPAL SECURITIES FUND INC
Prospectus Date	rr_ProspectusDate	May 31, 2016
Supplement [Text Block]	fmsfi_SupplementTextBlock	IMPORTANT INFORMATION REGARDING THE FEDERATED FUNDS SUPPLEMENT TO CURRENT PROSPECTUSES 1. Under the section entitled "Fund Summary Information," please add the following as the final sentence to the "Risk/Return Summary: Fees and Expenses" introductory paragraph:                                                  "More information about these and other discounts is available from your financial professional, in the "What Do Shares Cost?" section of the Prospectus and in "Appendix B" to this Prospectus."
FEDERATED MUNICIPAL SECURITIES FUND INC
Risk/Return:	rr_RiskReturnAbstract
Supplement [Text Block]	fmsfi_SupplementTextBlock	IMPORTANT INFORMATION REGARDING THE FEDERATED FUNDS SUPPLEMENT TO CURRENT PROSPECTUSES 1. Under the section entitled "Fund Summary Information," please add the following as the final sentence to the "Risk/Return Summary: Fees and Expenses" introductory paragraph:                                                  "More information about these and other discounts is available from your financial professional, in the "What Do Shares Cost?" section of the Prospectus and in "Appendix B" to this Prospectus."