Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ / shares in Thousands, $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Accounts receivable, allowance for credit losses	$ 11	$ 11
Series A Perpetual Preferred Stock, par value (in dollars per share)	$ 0	$ 0
Series A Perpetual Preferred Stock, shares authorized (in shares)	1,500,000	1,500,000
Series A Perpetual Preferred Stock, shares issued (in shares)	650,000	650,000
Series A Perpetual Preferred Stock, shares outstanding (in shares)	650,000	650,000
Series A Perpetual Preferred Stock, liquidation value	$ 650	$ 650
Common stock, par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	103,100,856	101,746,860
Common stock, shares outstanding (in shares)	89,112,965	92,658,362
Treasury stock (in shares)	13,987,891	9,088,498
Common Class A [Member]
Common stock, par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	25,000,000	25,000,000
Common stock, shares issued (in shares)	8,935,773	8,768,959
Common stock, shares outstanding (in shares)	7,048,006	6,881,192
Treasury stock (in shares)	1,887,767	1,887,767