That $58 billion is more than just money from bank accounts that have been escheated (turned over to the state) due to lack of activity.
From CNN Money:
Currently, states, federal agencies and other organizations collectively hold more than $58 billion in unclaimed cash and benefits. That's roughly $186 for every U.S. resident. The unclaimed property comes from a variety of sources, including abandoned bank accounts and stock holdings, unclaimed life insurance payouts and forgotten pension benefits. Read more
The article includes links to sites which can help you search for undeliverable tax refunds, life insurance, pensions, missing savings bonds, and overbid proceeds.