Why Credit Card Stocks Are So Volatile Today

Capital One Financial's (COF 1.20%) planned acquisition of Discover Financial Services (DFS 3.35%) has received regulatory approval, and investors are breathing a sigh of relief.Shares of Discover opened up 7% and Capital One up 5%, before retreating with the broader market to up 2% and 1% as of 11:30 a.m. ET. MasterCard (MA -2.30%) and Visa (V -3.47%) were headed in the other direction, both down about 3% midday.A credit card powerhouseCapital One and Discover are two of the biggest names in credit cards. ...