XML 55 R31.htm IDEA: XBRL DOCUMENT
v3.20.1

FINANCIAL HIGHLIGHTS - Per share performance data and other supplemental financial data (Details) - $ / shares | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Per Share Operating Performance: |  |  |  |  |
Net asset value, beginning of period | $ 24.35 | $ 23.34 | [1] | $ 37.18 | [1]
Total income (loss) | (7.16) | 1.30 |  | (13.49) |
Total expenses | (0.28) | (0.29) |  | (0.35) |
Net increase (decrease) in net asset value | (7.44) | 1.01 |  | (13.84) |
Net asset value, end of period | $ 16.91 | $ 24.35 |  | $ 23.34 | [1]
Total Return | (30.55%) | 4.33% |  | (37.22%) |
Ratios to Average Net Assets |  |  |  |  |
Total income (loss) | (24.25%) | 30.51% |  | (37.75%) |
Management fees | 0.60% | 0.60% |  | 0.60% |
Expenses excluding management fees | 0.73% | 0.68% |  | 0.70% |
Net income (loss) | (25.58%) | 29.23% |  | (39.05%) |
[1] | On January 4, 2018, there was a 1for4 reverse share split. The Statement of Changes in Partners’ Capital have been adjusted for the period shown to reflect the 1for4 reverse share split on a retroactive basis.

X
- Definition Average Net Assets [Abstract] + References No definition available. + Details
Name: | ung_AverageNetAssetsAbstract
Namespace Prefix: | ung_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Expenses, Excluding Management Fee Percentage + References No definition available. + Details
Name: | ung_ExpensesExcludingManagementFeePercentage
Namespace Prefix: | ung_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Increase (Decrease) In Net Asset Value Per Unit + References No definition available. + Details
Name: | ung_IncreaseDecreaseInNetAssetValuePerUnit
Namespace Prefix: | ung_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Management Incentive Fee Percentage + References No definition available. + Details
Name: | ung_ManagementIncentiveFeePercentage
Namespace Prefix: | ung_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Net asset value per unit. + References No definition available. + Details
Name: | ung_NetAssetValuePerUnit
Namespace Prefix: | ung_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage of Consolidated Net Income (Loss). + References No definition available. + Details
Name: | ung_PercentageOfConsolidatedNetIncomeLoss
Namespace Prefix: | ung_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of Total Revenue + References No definition available. + Details
Name: | ung_PercentageOfTotalRevenue
Namespace Prefix: | ung_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Rate Of Return On Average Asset + References No definition available. + Details
Name: | ung_RateOfReturnOnAverageAsset
Namespace Prefix: | ung_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Total Expenses, Per Unit + References No definition available. + Details
Name: | ung_TotalExpensesPerUnit
Namespace Prefix: | ung_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Total Income (Loss), Per Unit + References No definition available. + Details
Name: | ung_TotalIncomeLossPerUnit
Namespace Prefix: | ung_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | us-gaap_IncreaseDecreaseInPartnersCapitalRollForward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration