Consolidated Balance Sheet (Parentheticals) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Allowance for doubtful accounts	$ 7	$ 9
Debt issuance costs	$ 27	$ 28
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)	144,515,658	143,942,539
Treasury stock, shares (in shares)	10,442,582	10,111,191