v3.25.2
Shareholder Report, Average Annual Return (Details)
 12 Months Ended 19 Months Ended 60 Months Ended 120 Months Ended
May 31, 2025
May 31, 2025
May 31, 2025
May 31, 2025
Without Sales Load [Member] | C000005490        
Average Annual Return [Line Items]        
Average Annual Return, Percent 7.92%   7.34% 6.31%
Without Sales Load [Member] | C000005491        
Average Annual Return [Line Items]        
Average Annual Return, Percent 7.67%   7.08% 6.05%
Without Sales Load [Member] | C000005492        
Average Annual Return [Line Items]        
Average Annual Return, Percent 7.38%   6.81% 5.79%
Without Sales Load [Member] | C000244821        
Average Annual Return [Line Items]        
Average Annual Return, Percent 8.07% 13.32%    
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% 6.56%    
S&P Target Date 2020 Index        
Average Annual Return [Line Items]        
Average Annual Return, Percent 8.47%   6.18% 5.55%
S&P Target Date 2020 Index        
Average Annual Return [Line Items]        
Average Annual Return, Percent 8.47%   6.18% 5.55%
S&P Target Date 2020 Index        
Average Annual Return [Line Items]        
Average Annual Return, Percent 8.47%   6.18% 5.55%
S&P Target Date 2020 Index        
Average Annual Return [Line Items]        
Average Annual Return, Percent 8.47% 12.56%