Consolidated Balance Sheet (Current Period Unaudited) (Parentheticals) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Allowance for doubtful accounts	$ 7	$ 7
Debt issuance costs	$ 28	$ 27
Preferred stock, shares authorized (in shares)	50,000,000	50,000,000
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	450,000,000	450,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares outstanding (in shares)	144,228,817	144,515,658
Treasury stock, shares (in shares)	11,659,073	10,442,582