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S000010030 [Member] Average Annual Total Returns
12 Months Ended 60 Months Ended 120 Months Ended
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Bloomberg US Aggregate Bond Index      
Prospectus [Line Items]      
Average Annual Return, Percent [1] 7.30% (0.36%) 2.01%
Shares      
Prospectus [Line Items]      
Average Annual Return, Percent 7.11% 0.23% 2.46%
Shares | After Taxes on Distributions      
Prospectus [Line Items]      
Average Annual Return, Percent 5.56% (1.08%) 1.12%
Shares | After Taxes on Distributions and Sales      
Prospectus [Line Items]      
Average Annual Return, Percent 4.19% (0.39%) 1.30%
[1] The Bloomberg US Aggregate Bond Index is an unmanaged index that measures the investment grade, U.S. dollar denominated, fixed-rate taxable bond market, including treasuries, government-related and corporate securities, mortgage-backed securities, asset-backed securities, and commercial mortgage-backed securities. The Index figures do not reflect any deduction for fees, taxes or expenses.