v3.25.2
Shareholder Report, Holdings (Details)
May 31, 2025
C000005529 | U.S. Treasury Notes  
Holdings [Line Items]  
Percent of Net Asset Value 24.00%
C000005529 | U.S. Treasury Bonds  
Holdings [Line Items]  
Percent of Net Asset Value 13.00%
C000005529 | Federal National Mortgage Assn.  
Holdings [Line Items]  
Percent of Net Asset Value 10.60%
C000005529 | Federal Home Loan Mortgage  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
C000005529 | Government National Mortgage Assn.  
Holdings [Line Items]  
Percent of Net Asset Value 4.50%
C000005529 | Santander Drive Auto Receivables Trust  
Holdings [Line Items]  
Percent of Net Asset Value 1.10%
C000005529 | Bank of America  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
C000005529 | JPMorgan Chase  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
C000005529 | NRG Energy  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
C000005529 | Centene  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
C000005529 | U.S. Government Agency Obligations (Excluding Mortgage-Backed)  
Holdings [Line Items]  
Percent of Net Asset Value 37.10%
C000005529 | Corporate Bonds  
Holdings [Line Items]  
Percent of Net Asset Value 24.60%
C000005529 | U.S. Government & Agency Mortgage-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 20.20%
C000005529 | Asset-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 7.80%
C000005529 | Bank Loans  
Holdings [Line Items]  
Percent of Net Asset Value 3.80%
C000005529 | Non-U.S. Government Mortgage-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
C000005529 | Foreign Government Obligations & Municipalities  
Holdings [Line Items]  
Percent of Net Asset Value 1.30%
C000005529 | Securities Lending Collateral  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
C000005529 | Other Holdings Grouping  
Holdings [Line Items]  
Percent of Net Asset Value 1.40%
C000005530 | U.S. Treasury Notes  
Holdings [Line Items]  
Percent of Net Asset Value 24.00%
C000005530 | U.S. Treasury Bonds  
Holdings [Line Items]  
Percent of Net Asset Value 13.00%
C000005530 | Federal National Mortgage Assn.  
Holdings [Line Items]  
Percent of Net Asset Value 10.60%
C000005530 | Federal Home Loan Mortgage  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
C000005530 | Government National Mortgage Assn.  
Holdings [Line Items]  
Percent of Net Asset Value 4.50%
C000005530 | Santander Drive Auto Receivables Trust  
Holdings [Line Items]  
Percent of Net Asset Value 1.10%
C000005530 | Bank of America  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
C000005530 | JPMorgan Chase  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
C000005530 | NRG Energy  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
C000005530 | Centene  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
C000005530 | U.S. Government Agency Obligations (Excluding Mortgage-Backed)  
Holdings [Line Items]  
Percent of Net Asset Value 37.10%
C000005530 | Corporate Bonds  
Holdings [Line Items]  
Percent of Net Asset Value 24.60%
C000005530 | U.S. Government & Agency Mortgage-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 20.20%
C000005530 | Asset-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 7.80%
C000005530 | Bank Loans  
Holdings [Line Items]  
Percent of Net Asset Value 3.80%
C000005530 | Non-U.S. Government Mortgage-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
C000005530 | Foreign Government Obligations & Municipalities  
Holdings [Line Items]  
Percent of Net Asset Value 1.30%
C000005530 | Securities Lending Collateral  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
C000005530 | Other Holdings Grouping  
Holdings [Line Items]  
Percent of Net Asset Value 1.40%
C000005531 | U.S. Treasury Notes  
Holdings [Line Items]  
Percent of Net Asset Value 24.00%
C000005531 | U.S. Treasury Bonds  
Holdings [Line Items]  
Percent of Net Asset Value 13.00%
C000005531 | Federal National Mortgage Assn.  
Holdings [Line Items]  
Percent of Net Asset Value 10.60%
C000005531 | Federal Home Loan Mortgage  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
C000005531 | Government National Mortgage Assn.  
Holdings [Line Items]  
Percent of Net Asset Value 4.50%
C000005531 | Santander Drive Auto Receivables Trust  
Holdings [Line Items]  
Percent of Net Asset Value 1.10%
C000005531 | Bank of America  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
C000005531 | JPMorgan Chase  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
C000005531 | NRG Energy  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
C000005531 | Centene  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
C000005531 | U.S. Government Agency Obligations (Excluding Mortgage-Backed)  
Holdings [Line Items]  
Percent of Net Asset Value 37.10%
C000005531 | Corporate Bonds  
Holdings [Line Items]  
Percent of Net Asset Value 24.60%
C000005531 | U.S. Government & Agency Mortgage-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 20.20%
C000005531 | Asset-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 7.80%
C000005531 | Bank Loans  
Holdings [Line Items]  
Percent of Net Asset Value 3.80%
C000005531 | Non-U.S. Government Mortgage-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
C000005531 | Foreign Government Obligations & Municipalities  
Holdings [Line Items]  
Percent of Net Asset Value 1.30%
C000005531 | Securities Lending Collateral  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
C000005531 | Other Holdings Grouping  
Holdings [Line Items]  
Percent of Net Asset Value 1.40%
C000159679 | U.S. Treasury Notes  
Holdings [Line Items]  
Percent of Net Asset Value 24.00%
C000159679 | U.S. Treasury Bonds  
Holdings [Line Items]  
Percent of Net Asset Value 13.00%
C000159679 | Federal National Mortgage Assn.  
Holdings [Line Items]  
Percent of Net Asset Value 10.60%
C000159679 | Federal Home Loan Mortgage  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
C000159679 | Government National Mortgage Assn.  
Holdings [Line Items]  
Percent of Net Asset Value 4.50%
C000159679 | Santander Drive Auto Receivables Trust  
Holdings [Line Items]  
Percent of Net Asset Value 1.10%
C000159679 | Bank of America  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
C000159679 | JPMorgan Chase  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
C000159679 | NRG Energy  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
C000159679 | Centene  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
C000159679 | U.S. Government Agency Obligations (Excluding Mortgage-Backed)  
Holdings [Line Items]  
Percent of Net Asset Value 37.10%
C000159679 | Corporate Bonds  
Holdings [Line Items]  
Percent of Net Asset Value 24.60%
C000159679 | U.S. Government & Agency Mortgage-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 20.20%
C000159679 | Asset-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 7.80%
C000159679 | Bank Loans  
Holdings [Line Items]  
Percent of Net Asset Value 3.80%
C000159679 | Non-U.S. Government Mortgage-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
C000159679 | Foreign Government Obligations & Municipalities  
Holdings [Line Items]  
Percent of Net Asset Value 1.30%
C000159679 | Securities Lending Collateral  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
C000159679 | Other Holdings Grouping  
Holdings [Line Items]  
Percent of Net Asset Value 1.40%
C000219349 | U.S. Treasury Notes  
Holdings [Line Items]  
Percent of Net Asset Value 24.00%
C000219349 | U.S. Treasury Bonds  
Holdings [Line Items]  
Percent of Net Asset Value 13.00%
C000219349 | Federal National Mortgage Assn.  
Holdings [Line Items]  
Percent of Net Asset Value 10.60%
C000219349 | Federal Home Loan Mortgage  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
C000219349 | Government National Mortgage Assn.  
Holdings [Line Items]  
Percent of Net Asset Value 4.50%
C000219349 | Santander Drive Auto Receivables Trust  
Holdings [Line Items]  
Percent of Net Asset Value 1.10%
C000219349 | Bank of America  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
C000219349 | JPMorgan Chase  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
C000219349 | NRG Energy  
Holdings [Line Items]  
Percent of Net Asset Value 0.60%
C000219349 | Centene  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
C000219349 | U.S. Government Agency Obligations (Excluding Mortgage-Backed)  
Holdings [Line Items]  
Percent of Net Asset Value 37.10%
C000219349 | Corporate Bonds  
Holdings [Line Items]  
Percent of Net Asset Value 24.60%
C000219349 | U.S. Government & Agency Mortgage-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 20.20%
C000219349 | Asset-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 7.80%
C000219349 | Bank Loans  
Holdings [Line Items]  
Percent of Net Asset Value 3.80%
C000219349 | Non-U.S. Government Mortgage-Backed Securities  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
C000219349 | Foreign Government Obligations & Municipalities  
Holdings [Line Items]  
Percent of Net Asset Value 1.30%
C000219349 | Securities Lending Collateral  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
C000219349 | Other Holdings Grouping  
Holdings [Line Items]  
Percent of Net Asset Value 1.40%