Americans' retirement assets declined 5.9% in the third quarter, to $15.9 trillion, even before the stock market reached a November low, according to the Investment Company Institute.

Individual investors lost significant chunks of their retirement savings during the market's slow-motion crash last autumn. Since then dozens of companies, looking to cut costs, have ended contributions to employees' 401(k) plans.

The $15.9 trillion accounted for 35% of all household financial assets in the United States as of Sept. 30, the institute said last week.

Among vehicle types, individual retirement accounts held the most consumer retirement assets, with $4.1 trillion, followed by employer-sponsored defined contribution plans, with $4 trillion.

Forty-six percent of IRA assets and 47% of defined contribution assets were invested in mutual funds, according to data issued by the ICI. The total third-quarter return on equities was negative-8.4%, and the total return on bonds was negative-0.1%.

The ICI's data covers assets in private-sector pension plans, including defined benefit and contribution plans, government plans, annuities, and IRAs.

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