| In millions, except per share items | Jun-30-23 | Mar-31-23 | Dec-31-22 | Sep-30-22 | Jun-30-22 | Mar-31-22 | Dec-31-21 | Sep-30-21 |
| | 10-Q | 10-Q | 10-K | 10-Q | 10-Q | 10-Q | 10-K | 10-Q |
| Cash Flows from Operating Activities: | | | | | | | | |
| Net income (loss) | -55.4 | -21.4 | 82.6 | 80.1 | 136.1 | 170.7 | 157.5 | 220.7 |
| Adjustments to reconcile net income (loss) to net cash from (used in) operating activities: | | | | | | | | |
| Change in unrealized (gain) loss on open commodity futures contracts | -4.1 | -24.6 | -2.8 | 24.0 | 11.6 | -2.2 | -10.3 | -19.9 |
| (Increase) decrease in related party receivable | | | | | | 0.0 | -4.5 | |
| (Increase) decrease in dividends receivable | -0.1 | -0.4 | -0.4 | -0.1 | -0.1 | 0.0 | 0.0 | 0.0 |
| (Increase) decrease in interest receivable | -0.4 | -0.4 | -0.3 | -0.2 | 0.0 | 0.0 | 0.0 | 0.0 |
| (Increase) decrease in prepaid insurance | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| (Increase) decrease in ETF transaction fees receivable | 0.0 | 0.0 | | 0.0 | 0.0 | 0.0 | | |
| Increase (decrease) in General Partner management fees payable | -0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | -0.1 | -0.1 |
| Increase (decrease) in professional fees payable | -0.1 | 0.1 | 0.2 | 0.3 | 0.0 | 0.1 | 0.1 | 0.1 |
| Increase (decrease) in brokerage commissions payable | 0.0 | | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Increase (decrease) in directors' fees payable | 0.0 | 0.0 | | | 0.0 | 0.0 | 0.0 | |
| Increase (decrease) in registration fees payable | | | | -0.1 | 0.3 | 0.2 | 0.2 | 0.1 |
| Net cash provided by (used in) operating activities | -60.5 | -47.0 | 83.6 | 103.9 | 147.9 | 169.0 | 143.6 | 201.5 |
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| Cash Flows from Financing Activities: | | | | | | | | |
| Addition of partnership shares | 164.1 | 275.8 | 234.5 | 192.1 | 171.0 | 64.8 | 68.4 | 46.8 |
| Redemption of partnership shares | -223.0 | -295.4 | -309.0 | -319.1 | -350.4 | -284.7 | -347.3 | -379.1 |
| Net cash provided by (used in) financing activities | -58.9 | -19.6 | -74.5 | -127.0 | -179.4 | -219.9 | -278.9 | -332.3 |
| Net Increase (Decrease) in Cash and Cash Equivalents | -119.3 | -66.6 | 9.1 | -23.1 | -31.5 | -51.0 | -135.4 | -130.8 |
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| Components of Cash, Cash Equivalents, and Equity in Trading Accounts | | | | | | | | |
| Cash and cash equivalents | | | | | | | | |
| Equity in Trading Accounts: | | | | | | | | |
| Cash and cash equivalents | | | | | | | | |