v3.25.2
S000006334 [Member] Average Annual Total Returns
 12 Months Ended 58 Months Ended 60 Months Ended 120 Months Ended 310 Months Ended 420 Months Ended
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
Bloomberg U.S. Aggregate Bond Index (reflects no deduction for fees, expenses or taxes)            
Prospectus [Line Items]            
Average Annual Return, Percent [1] 1.25% 4.99% (0.33%) 1.35%    
I Class            
Prospectus [Line Items]            
Average Annual Return, Percent [2] 0.75%   (0.40%) 1.20%   5.00%
Performance Inception Date [2]           Jan. 01, 1990
I Class | After Taxes on Distributions            
Prospectus [Line Items]            
Average Annual Return, Percent [2] (0.99%)   (1.60%) 0.05%   3.40%
Performance Inception Date [2]           Jan. 01, 1990
I Class | After Taxes on Distributions and Sales            
Prospectus [Line Items]            
Average Annual Return, Percent [2] 0.44%   (0.77%) 0.44%   3.36%
Performance Inception Date [2]           Jan. 01, 1990
N Class            
Prospectus [Line Items]            
Average Annual Return, Percent 0.59%   (0.57%) 0.98% 3.89%  
Performance Inception Date         Mar. 01, 1999  
Plan Class            
Prospectus [Line Items]            
Average Annual Return, Percent 0.72% (1.05%)    
Performance Inception Date   Feb. 28, 2020        
[1]
The Bloomberg U.S. Aggregate Bond Index is a market capitalization-weighted index of investment grade, U.S. dollar-denominated, fixed-rate debt issues, including Treasuries, government-related and corporate securities, mortgage-backed securities (agency fixed-rate and hybrid adjustable-rate mortgage), asset-backed securities and commercial mortgage-backed securities (agency and non‑agency).
[2]
Performance data includes the performance of the predecessor entity for periods before the Fund’s registration became effective. The predecessor entity was not registered under the 1940 Act and, therefore, was not subject to certain investment restrictions that are imposed by the 1940 Act. If the predecessor entity had been registered under the 1940 Act, the predecessor entity’s performance may have been lower.