Note 2 - Significant Accounting Policies - Share Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Shares issued (in shares)	53,400,000	83,500,000	53,075,000	[1]
Shares issued, amount	$ 1,988,659,596	$ 2,989,014,129	$ 1,853,104,516
Shares redeemed (in shares)	(137,050,000)	(152,550,000)	(108,550,000)	[1]
Distributions for Shares redeemed	$ (4,970,554,906)	$ (5,018,182,038)	$ (3,649,216,540)
Net decrease in Shares issued and outstanding (in shares)	(83,650,000)	(69,050,000)	(55,475,000)
Net increase (decrease) in net assets from capital share transactions	$ (2,981,895,310)	$ (2,029,167,909)	$ (1,796,112,024)

[1] Share transactions reflect a one-for-two reverse stock split effective at market open on May 24, 2021.