A 3.1 percent decrease in the Tennessee Valley Authority's fuel cost will bring down average residential electric bills in January by between $2 and $4.

TVA said in a statement on Wednesday that the decrease is related to hydroelectric generation in November that was almost 30 percent higher than expected. That meant the utility did not have to rely as much on more expensive sources of electricity. Also sales were slightly lower than expected.

The decrease follows a 2.8 percent increase in December.

TVA is the nation's largest public utility and supplies power to about 9 million people in Tennessee, Kentucky, Alabama, Mississippi, Georgia, North Carolina and Virginia.