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Statements of Changes in Partners' Capital (Parenthetical) - shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Addition of partnership units 410,300,000 456,900,000 573,900,000
Redemption of partnership units 508,100,000 475,100,000 354,100,000