Consolidated Balance Sheets (unaudited) (Parenthetical) - $ / shares shares in Millions	Sep. 30, 2020	Dec. 31, 2019
Treasury stock (in shares)	221	190
Series A-1 Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock authorized (in shares)	8	8
Preferred stock issued (in shares)	8	8
Preferred stock outstanding (in shares)	8	8
Series C-1 Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock authorized (in shares)	6	6
Preferred stock issued (in shares)	5	5
Preferred stock outstanding (in shares)	5	5
Series A Common Stock
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock authorized (in shares)	1,700	1,700
Common stock issued (in shares)	163	161
Common stock outstanding (in shares)	160	158
Series B Common Stock
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock authorized (in shares)	100	100
Common stock issued (in shares)	7	7
Common stock outstanding (in shares)	7	7
Series C Common Stock
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock authorized (in shares)	2,000	2,000
Common stock issued (in shares)	546	547
Common stock outstanding (in shares)	329	360