XML 47 R31.htm IDEA: XBRL DOCUMENT
v3.20.4

FINANCIAL HIGHLIGHTS - Per share performance data and other supplemental financial data (Details) - $ / shares | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | [1]
Per Share Operating Performance: |  |  |  |
Net asset value, beginning of year | $ 16.91 | $ 24.35 | [1] | $ 23.34
Total income (loss) | (7.55) | (7.16) |  | 1.30
Total expenses | (0.16) | (0.28) |  | (0.29)
Net increase (decrease) in net asset value | (7.71) | (7.44) |  | 1.01
Net asset value, end of year | $ 9.20 | $ 16.91 |  | $ 24.35
Total Return | (45.59%) | (30.55%) |  | 4.33%
Ratios to Average Net Assets |  |  |  |
Total income (loss) | (49.07%) | (24.25%) |  | 30.51%
Management fees | 0.60% | 0.60% |  | 0.60%
Expenses excluding management fees | 0.75% | 0.73% |  | 0.68%
Net income (loss) | (50.42%) | (25.58%) |  | 29.23%
[1] | On January 4, 2018, there was a 1-for-4 reverse share split. Historical shares outstanding, net asset value per share and market value per share have been adjusted for the period shown to reflect the 1-for-4 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: | duration

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