Principal Financial Group Inc. reported fourth-quarter operating earnings of $243.9 million, a 21 percent increase from $201.8 million in operating earnings in fourth quarter of 2011, the company said in a release.  Net income available to common stockholders was $218.6 million, or 74 cents per share, compared with $148.5 million, or 48 cents per share for the year-ago period. The company also announced that its board of directors has declared a quarterly dividend of 23 cents per share of common stock, an increase of 10 percent over the fourth-quarter 2012 dividend. "The continued strength of our underlying business fundamentals and successful execution of our strategy gives us momentum going into 2013," said Larry Zimpleman, chairman, president and CEO, in a release.