LANSING, Mich. (AP) - Michigan regulators plan to investigate power outages stemming from a pre-Christmas holiday ice storm that knocked out service to about 660,000 customers. The state Public Service Commission is expected to approve the order at a meeting Wednesday. Scores of tree branches broke and fell from the weight of ice during the storm. Consumers Energy and DTE Energy, Michigan's largest utilities, say they restored power within a week of the storm that hit Dec. 21-22. Customers without electricity for more than 120 hours may be eligible for a $25 credit. In 2009, regulators told major utilities to make changes after residents were frustrated by long power outages caused by storms. Changes included better notifying customers of the $25 credit.