Genworth Financial Inc. posted the biggest gain in the Standard & Poor’s 500 Index on Chief Executive Officer Tom McInerney’s plan to distance the mortgage-guaranty unit from the rest of the company.

The insurer rallied 13 percent to $9.16 at 9:42 a.m. in New York trading.

McInerney, who became CEO this month, is working to revamp the insurer after losses from the mortgage unit drained capital and threatened the firm’s investment-grade credit rating. The Richmond, Virginia-based company also sells life insurance and long-term care coverage. Genworth said today it will create a new parent company and the outstanding senior and subordinated notes will remain obligations of the old parent.

“The transaction validates our thesis that Genworth could unlock value” and avert a ratings downgrade, said Mark Palmer an analyst at BTIG LLC, in a note to investors today. “We believe it should provide a significant boost to the company’s shares.”