Consolidated Balance Sheet (Current Period Unaudited) (Parentheticals) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Allowance for doubtful accounts	$ 6	$ 7
Debt issuance costs	$ 26	$ 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
Preferred stock, shares outstanding (in shares)	0	0
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)	145,142,687	144,515,658
Treasury stock, shares (in shares)	10,657,998	10,442,582