A December report from Cerulli Associates found retirement assets in the United States rose 4.7% from 2009 to about $15 trillion in 2010. Analysts estimated assets could surpass $20 trillion by 2015.

Assets in IRAs have grown faster than in other accounts, according to a summary of the report. As of the end of 2009, IRA assets were near $4.3 trillion, a compound annual growth rate of 5.5% over nine years. On Dec. 1, the Investment Company Institute reported that IRAs held $4.2 trillion in assets, more than one-quarter of all retirement wealth in the United States for the second quarter of 2010.

While defined-benefit plans have declined, according to Cerulli, there are still opportunities for "institutional consultants with strong actuarial capabilities and LDI expertise, as more plans will freeze in the future to reduce funding volatility."

"As the demographic factors for DC plans shift due to looming baby boomer retirements, a successful retirement income focus will provide another income stream for retirees," according to the report.

"With DB plans waning and Social Security in jeopardy, DC and IRA plan providers must create and implement better strategies to generate reliable income for America’s next generation of retirees."

Nearly $185 billion in 401(k) assets could change hands in 2011, Cerulli estimates, primarily in plans with less than $10 million.