Contracts And Agreements (Additional Information) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Annual Fee for transfer agency services	$ 20,000
Brokerage commissions	8,360	14,360	7,002
Rebalancing Cost	4,484	10,995	6,306
Creation And Redemption Activity Costs	3,876	3,365	696
Average Daily Total Net Asset Percentage	0.03%	0.04%	0.02%
Brokerage Commission Rebalancing Cost Of Percentage	53.64%	76.57%	90.06%
Creation And Redemption Activity Costs Of Percentage	46.36%	23.43%	9.94%
Maximum [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Transaction fees per transaction	15
Commissions per round-turn trade, including applicable exchange and NFA fees for Natural Gas-Related Futures Contracts and options on Futures Contracts	15
Minimum [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Annual Fee for custody, fund accounting and fund administration services	75,000
Transaction fees per transaction	7
Commissions per round-turn trade, including applicable exchange and NFA fees for Natural Gas-Related Futures Contracts and options on Futures Contracts	7
First $500 million of Related Public Funds’ combined net assets [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Fee percentage	0.06%
First $500 million of Related Public Funds’ combined net assets [Member] | Maximum [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Base amount for determining fee percentage	500,000,000
Related Public Funds’ combined net assets greater than $500 million but less than $1 billion [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Fee percentage	0.0465%
Related Public Funds’ combined net assets greater than $500 million but less than $1 billion [Member] | Maximum [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Base amount for determining fee percentage	1,000,000,000
Related Public Funds’ combined net assets greater than $500 million but less than $1 billion [Member] | Minimum [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Base amount for determining fee percentage	500,000,000
Related Public Funds’ combined net assets exceed $1 billion [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Fee percentage	0.035%
Related Public Funds’ combined net assets exceed $1 billion [Member] | Minimum [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Base amount for determining fee percentage	1,000,000,000
Marketing Agreement [Member] | UNL's assets up to $3 billion [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Fee percentage	0.06%
Marketing Agreement [Member] | UNL's assets up to $3 billion [Member] | Maximum [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Base amount for determining fee percentage	3,000,000,000
Marketing Agreement [Member] | UNL's assets in excess of $3 billion [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Fee percentage	0.04%
Marketing Agreement [Member] | UNL's assets in excess of $3 billion [Member] | Minimum [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Base amount for determining fee percentage	$ 3,000,000,000