Feb. 6 (Bloomberg) -- Winter storms that brought heavy snowfall, freezing rain and Arctic air to the U.S. last month will probably cost more than $3.5 billion in economic losses, according to insurance broker Aon Plc.

Insurers estimated losses of more than $1.4 billion from the second week of January, the most costly of four extreme- weather periods during the month, the London-based broker said today in a report. Insured losses from the three other stretches totaled about $200 million.

At least 21 people were killed from Jan. 5 through 8, as more than 20 inches (51 centimeters) of snow fell in the Great Lakes region and Ohio Valley and freezing rain pelted the Northeast and Mid-Atlantic. Widespread property damage and severe travel delays added to the costs.