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MassMutual Select Total Return Bond Fund  
Risk/Return: rr_RiskReturnAbstract  
Supplement to Prospectus [Text Block] rr_SupplementToProspectusTextBlock
MASSMUTUAL SELECT FUNDS
MassMutual Select Total Return Bond Fund
(the “Fund”)
Supplement dated November 20, 2020 to the
Prospectus dated February 1, 2020 and the
Summary Prospectus dated February 1, 2020

This supplement provides new and additional information beyond that contained in the Prospectus and Summary Prospectus, and any previous supplements. It should be retained and read in conjunction with the Prospectus and Summary Prospectus, and any previous supplements.
Risk/Return [Heading] rr_RiskReturnHeading MassMutual Select Total Return Bond Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
Effective November 20, 2020, the following information replaces similar information for the Fund found under the headings Annual Fund Operating Expenses and Example in the section titled Fees and Expenses of the Fund (on page 3 of the Prospectus):
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination Jan. 31, 2022
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. It assumes that you invest $10,000 in each share class of the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. For Class A shares, the example includes the initial sales charge. The example also assumes that your investment earns a 5% return each year and that the Fund’s operating expenses are exactly as described in the preceding table. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example Closing [Text Block] rr_ExpenseExampleClosingTextBlock
PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE
MassMutual Select Total Return Bond Fund | Class I  
Risk/Return: rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.30%
Distribution and Service (Rule 12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.06%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.36%
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets (0.03%)
Total Annual Fund Operating Expenses after Fee Waiver rr_NetExpensesOverAssets 0.33% [1]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 34
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 113
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 199
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 453
MassMutual Select Total Return Bond Fund | Class R5  
Risk/Return: rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.30%
Distribution and Service (Rule 12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.16%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.46%
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets (0.03%)
Total Annual Fund Operating Expenses after Fee Waiver rr_NetExpensesOverAssets 0.43% [1]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 44
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 145
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 255
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 576
MassMutual Select Total Return Bond Fund | Service Class  
Risk/Return: rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.30%
Distribution and Service (Rule 12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.26%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.56%
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets (0.03%)
Total Annual Fund Operating Expenses after Fee Waiver rr_NetExpensesOverAssets 0.53% [1]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 54
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 176
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 309
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 698
MassMutual Select Total Return Bond Fund | Administrative Class  
Risk/Return: rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.30%
Distribution and Service (Rule 12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.36%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.66%
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets (0.03%)
Total Annual Fund Operating Expenses after Fee Waiver rr_NetExpensesOverAssets 0.63% [1]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 64
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 208
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 365
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 820
MassMutual Select Total Return Bond Fund | Class A  
Risk/Return: rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.30%
Distribution and Service (Rule 12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.36%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.91%
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets (0.03%)
Total Annual Fund Operating Expenses after Fee Waiver rr_NetExpensesOverAssets 0.88% [1]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 511
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 700
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 905
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,494
MassMutual Select Total Return Bond Fund | Class R4  
Risk/Return: rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.30%
Distribution and Service (Rule 12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.26%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.81%
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets (0.03%)
Total Annual Fund Operating Expenses after Fee Waiver rr_NetExpensesOverAssets 0.78% [1]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 80
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 256
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 447
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 999
MassMutual Select Total Return Bond Fund | Class R3  
Risk/Return: rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.30%
Distribution and Service (Rule 12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses rr_OtherExpensesOverAssets 0.26%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.06%
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets (0.03%)
Total Annual Fund Operating Expenses after Fee Waiver rr_NetExpensesOverAssets 1.03% [1]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 105
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 334
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 582
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,291
[1] The expenses in the above table reflect a written agreement by MML Advisers to waive .03% of its management fees through January 31, 2022. This agreement can only be terminated by mutual consent of the Board of Trustees on behalf of the Fund and MML Advisers.