Label

Element

Value

MFS® Government Securities Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement [Text Block]

ck0000356349_SupplementTextBlock

SUPPLEMENT TO PROSPECTUS

The date of this supplement is September 27, 2013.

For Certain MFS® Funds:

Risk/Return [Heading]

rr_RiskReturnHeading

MFS® Government Securities Fund

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

Effective immediately, in the second paragraph of the sub-section entitled “Fees and Expenses” beneath the main heading “Summary of Key Information,” the reference to the page number of the “Waivers of Sales Charges” is replaced by reference to page H-1 of the fund’s Statement of Additional Information (“SAI”).