DES MOINES, Iowa--(BUSINESS WIRE)--Principal Financial Group, Inc. (NYSE: PFG) today announced results for second quarter 2015. Operating earnings increased to $323.9 million for second quarter 2015, compared to $323.1 million for second quarter 2014. After adjusting for normalizing items and foreign exchange rates, operating earnings increased 10 percent over second quarter 2014. Operating earnings per diluted share (EPS) increased 1 percent to $1.09 for second quarter 2015, compared to $1.08