In defending himself against lawsuits from women who say he sexually assaulted and then defamed them, Bill Cosby is facing mountainous legal expenses. Luckily for him, he has homeowners’ insurance. That is the surprising tool Mr. Cosby is using to pay his legal fees as he battles defamation claims filed by 10 women in three states. Mr. Cosby’s insurer, American International Group, better known as A.I.G., has gone to court to deny him coverage, arguing, among other things, that it should not have to cover claims that arose from alleged acts of sexual misconduct. But so far, Mr. Cosby is winning.