WASHINGTON (AP) — American consumers stepped up their borrowing by $18.4 billion in December, a solid performance that followed a massive gain the previous month.

The Federal Reserve says the increase reflects gains of $5.1 billion in the category that covers credit cards and $13.3 billion in the category for auto and student loans.

The overall increase followed a $31 billion surge in November as consumers took on extra credit to finance holiday shopping.

Consumer borrowing is closely followed for indications about how confident households are in taking on more debt to finance spending, which accounts for 70 percent of economic activity. In the fourth quarter, the overall economy grew at a solid 2.6 percent rate. In recent months, Americans have been increasingly confident and willing to take on more debt.