Total U.S. retirement assets were $18.5 trillion at the end of the second quarter, 2 percent less than they were at March 31, reports the Investment Company Institute.

The decrease in retirement assets was driven by the drop in corporate equity values -- for example, the S&P 500 Index fell by 2.8 percent in the second quarter, ICI says. Retirement savings accounted for 36 percent of all household financial assets in the United States at June 30.
Assets in individual retirement accounts also dropped 2 percent during the second quarter to $5.1 trillion, the ICI says. Forty-six percent of IRA assets, or $2.3 trillion, were invested in mutual funds.

Defined contribution plan assets fell 2.2 percent in the second quarter to $4.7 trillion. Of the total, $3.3 trillion was held in 401(k) plans.

Government pension plans -- including federal, state and local government plans -- held $4.6 trillion in assets as of the end of June, a 1.5 percent decrease from the end of March. Private-sector defined benefit plans held $2.4 trillion in assets at the end of the second quarter of 2012, and annuity reserves outside of retirement accounts accounted for another $1.6 trillion.

As of June 30, target-date mutual fund assets totaled $427 billion, an increase of 0.5 percent in the second quarter. Retirement accounts held the bulk of target-date mutual fund assets: 91 percent of target date mutual fund assets were held through DC plans and IRAs.