- Getty Images The most extraordinary development in the U.S. private-sector retirement system is not the shift away from old-fashioned defined-benefit plans that began around 1980 and is virtually complete today. Instead, it’s the movement away from 401(k) plans, which replaced the defined-benefit plans, and toward individual retirement accounts. Total IRA assets now exceed the amount in 401(k) plans by $7 trillion (see Figure 1). Most Read from MarketWatch - The shift from 401(k)s to IRAs moves emp ...