Federal Employees' Retirement System: Budget and Trust Fund Issues [Updated December 13, 2019] [open pdf - 1MB]
From the Introduction: "Pensions for civilian federal employees are provided through two programs, the Civil Service Retirement System (CSRS) and the Federal Employees' Retirement System (FERS). CSRS was authorized by the Civil Service Retirement Act of 1920 (P.L. 66-215) and FERS was established by the Federal Employees' Retirement System Act of 1986 (P.L. 99-335). Under both CSRS and FERS, employees and their employing agencies make contributions to the Civil Service Retirement and Disability Fund (CSRDF), from which pension benefits are paid to retirees and their surviving dependents. Retirement and disability benefits under FERS are fully funded by employee and employer contributions and interest earned by the bonds in which the contributions are invested. The cost of the retirement and disability benefits earned by employees covered by CSRS, on the other hand, are not fully funded by agency and employee contributions and interest income. The federal government therefore makes supplemental payments each year into the civil service trust fund on behalf of employees covered by CSRS. Even with these additional payments into the trust fund, however, CSRS pensions are not fully pre-funded."
CRS Report for Congress, RL30023
Congressional Research Service: https://crsreports.congress.gov/