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)	167,250,000	175,900,000	275,950,000
Shares issued	$ 3,580,116,083	$ 3,608,993,778	$ 6,742,609,430
Shares redeemed (in shares)	(196,800,000)	(243,150,000)	(303,100,000)
Distributions for Shares redeemed	$ (4,222,040,407)	$ (4,680,125,800)	$ (7,174,837,696)
Net decrease in Shares issued and outstanding (in shares)	(29,550,000)	(67,250,000)	(27,150,000)
Net decrease in net assets from capital share transactions	$ (641,924,324)	$ (1,071,132,022)	$ (432,228,266)