Employers are expanding the scope of their 401(k) plans with increased matching contributions, relaxed eligibility rules and access to expert advice, an Aon Hewitt survey released Wednesday said.

Three-quarters (77 percent) of the more than 400 employers surveyed said a defined contribution plan was the primary retirement vehicle offered to their employees. The most frequent reasons given by employers when asked how they define the success of their DC plans were "facilitates adequate retirement income" (18 percent) and "high participation rate" (17 percent).

Nearly all of the surveyed employers (98 percent) – who collectively represent more than 10 million workers and $500 billion in retirement assets – contribute in some way to employee accounts. The company match to employee contributions is on the rise. The most popular match was $1 for every $1 up to 6 percent of salary with one-fifth (19 percent) of employers matching at that level, up from 11 percent in 2011. A 50-cents-on-the-dollar match had been the most popular rate in the past, Aon Hewitt said.