Hybrid retirement plans that combine the best features of defined benefit and defined contribution plans can provide an efficient and equitable method of ensuring retirement security for workers. Co-operative pension structures also enhance retirement security through risk pooling and leveraging economies of scale. Yet most U.S. private sector workers are not covered by these types of plan design. The TIAA-CREF system, which began in 1918 and covers millions of workers in the non-profit sector, provides an example of a plan design with features of a hybrid co-operative pension. We examine the historical performance of the core components, TIAA (a guaranteed fixed annuity) and CREF (a variable annuity), discuss key design features, and analyze data on contributions, investment returns, risk pooling, and retirement distribution characteristics.