DETROIT (AP) - The estate of former Detroit Pistons owner Bill Davidson is challenging the government in U.S. Tax Court over billions of dollars claimed by the IRS. The Detroit Free Press says the Internal Revenue Service objects to how Davidson's accountants valued stock in his company, Guardian Industries, which makes glass and parts for the auto industry. Other key issues include tens of millions of dollars given to Davidson's wife, Karen, and money used to help her daughter build a home in Bloomfield Hills. The Free Press says Davidson also canceled debts to heirs when he died, giving them ownership of certain assets. The newspaper says the IRS is seeking about $2 billion or more in estate taxes. The agency declined to comment. Davidson died in 2009 at age 86.