The Securities and Exchange Commission is investigating whether Bank of America Corp. violated customer-protection rules and put retail-brokerage funds at risk to increase profits, the Wall Street Journal reported, citing people familiar with the matter.

The bank used large, complex trades and loans to save millions of dollars a year in funding costs and to free up billions of dollars in cash and securities for trading that it otherwise would have needed to keep off-limits, the Journal reported.

The trades took place in the bank's Merrill Lynch unit, which it bought in 2009, according to the report.

Bank of America stopped the strategy in 2012. However, from 2009 to 2012, it completed billions of dollars' worth of such trades, the Journal said.

At times, the trades reduced the amount the bank had in lockup accounts by as much as $5 billion out of a total of up to about $20 billion in lockup, Wall Street Journal reported citing its sources.

The SEC is also evaluating the accuracy of the bank's prior statements to the agency, the report said.