Statements of Changes in Net Assets - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Assets, Beginning of Year	$ 7,310,131,020	$ 5,209,802,846	$ 6,213,387,199
Operations:
Net investment loss	(21,630,631)	(20,312,154)	(15,245,766)
Net realized gain (loss)	22,215,914	25,068,804	(87,792,181)
Net change in unrealized appreciation/depreciation	881,278,079	303,987,270	(659,078,052)
Net increase (decrease) in net assets resulting from operations	881,863,362	308,743,920	(762,115,999)
Capital Share Transactions:
Contributions for Shares issued	2,782,113,163	3,784,339,342	830,130,993
Distributions for Shares redeemed	(826,600,408)	(1,992,755,088)	(1,071,599,347)
Net increase (decrease) in net assets from capital share transactions	1,955,512,755	1,791,584,254	(241,468,354)
Increase (decrease) in net assets	2,837,376,117	2,100,328,174	(1,003,584,353)
Net Assets, End of Year	$ 10,147,507,137	$ 7,310,131,020	$ 5,209,802,846
Shares issued and redeemed
Shares issued (in shares)	228,250,000	314,850,000	72,050,000
Shares redeemed (in shares)	(68,350,000)	(167,950,000)	(99,350,000)
Net increase (decrease) in Shares issued and outstanding (in shares)	159,900,000	146,900,000	(27,300,000)