Wall Street employees, who dispense financial advice to individuals and companies, aren't following a basic investing tenet with their own money: diversification.

Workers at the five largest Wall Street banks saw the value of company stock in their 401(k) accounts, sometimes the biggest holding of those plans, decline more than $2 billion last year, according to annual filings. Those losses don't include shares received as bonuses.

The 2001 collapse of Enron Corp. led to warnings that tying retirement funds to an employer's stock could be more crippling when a company fails, resulting in the loss of both a nest egg as well as a source of income. Traders and bankers felt the pain of last year's decline in revenue from job cuts and lower bonuses in addition to the shrinking of their 401(k) accounts.