Whenever government sees something big, it either wants to tax it or confiscate it.
Here's the data about retirement assets for 2008, according to the Investment Company Institute, totaling just over $14 trillion:
IRA assets = $3.613 trillion
Defined contribution plans (401Ks, 403(b)s, 457s, etc.) = $3.517 trillion
Defined benefit plans (private sector pensions, government pensions, life insurance company annuities, etc.) = $6.9 trillion.
In 2007 such assets totaled nearly $18 trillion.