v3.25.2
Shareholder Report, Average Annual Return (Details)
 12 Months Ended 60 Months Ended 63 Months Ended 117 Months Ended 120 Months Ended
May 31, 2025
May 31, 2025
May 31, 2025
May 31, 2025
May 31, 2025
Without Sales Load [Member] | C000005529          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.18% (0.67%)     1.16%
Without Sales Load [Member] | C000005530          
Average Annual Return [Line Items]          
Average Annual Return, Percent 4.68% (1.12%)     0.79%
Without Sales Load [Member] | C000005531          
Average Annual Return [Line Items]          
Average Annual Return, Percent 4.52% (1.29%)     0.53%
Without Sales Load [Member] | C000159679          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.41% (0.56%)   1.39%  
Without Sales Load [Member] | C000219349          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.64% (0.20%) 0.11%    
Bloomberg U.S. Aggregate Bond Index          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.46% (0.90%)     1.49%
Bloomberg U.S. Aggregate Bond Index          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.46% (0.90%)     1.49%
Bloomberg U.S. Aggregate Bond Index          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.46% (0.90%)     1.49%
Bloomberg U.S. Aggregate Bond Index          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.46% (0.90%)   1.58%  
Bloomberg U.S. Aggregate Bond Index          
Average Annual Return [Line Items]          
Average Annual Return, Percent 5.46% (0.90%) (0.46%)