XML 29 R3.htm IDEA: XBRL DOCUMENT
v3.20.1

Schedule of Investments - USD ($) | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Value/ Unrealized Gain (Loss) on Open Commodity Contracts | $ (20,768,690) |  | $ (67,021,257) |
Open Futures Contracts - Long [Member] | United States Contracts |  |  |  |
Notional Amount | $ 465,354,590 | [1] | $ 315,010,257 | [2]
Number of Contracts | 20,310 | [1] | 12,935 | [2]
Value/ Unrealized Gain (Loss) on Open Commodity Contracts | $ (20,768,690) | [1] | $ (67,021,257) | [2]
% of Partners' Capital | (4.67%) | [1] | (27.02%) | [2]
Open Futures Contracts - Long [Member] | United States Contracts | NYMEX Natural Gas Futures NG February 2019 contracts, expiring January 2019 [Member] |  |  |  |
Notional Amount |  |  | $ 259,275,882 |
Number of Contracts |  |  | 6,935 |
Value/ Unrealized Gain (Loss) on Open Commodity Contracts |  |  | $ (55,386,882) |
% of Partners' Capital |  |  | (22.33%) |
Open Futures Contracts - Long [Member] | United States Contracts | ICE Natural Gas Futures LD1 H February 2019 contracts, expiring February 2019 [Member] |  |  |  |
Notional Amount |  |  | $ 55,734,375 |
Number of Contracts |  |  | 6,000 |
Value/ Unrealized Gain (Loss) on Open Commodity Contracts |  |  | $ (11,634,375) |
% of Partners' Capital |  |  | (4.69%) |
Cash Equivalents [Member] |  |  |  |
Market Value | $ 418,959,876 |  | $ 272,193,228 |
% of Partners' Capital | 94.24% |  | 109.75% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] |  |  |  |
Market Value | $ 258,959,876 |  | $ 238,493,228 |
% of Partners' Capital | 58.25% |  | 96.16% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.10%, 1/03/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,998,847 |
% of Partners' Capital |  |  | 4.03% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.10%, 1/10/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,994,800 |
% of Partners' Capital |  |  | 4.03% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.13%, 1/17/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,990,622 |
% of Partners' Capital |  |  | 4.03% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.15%, 1/24/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,986,423 |
% of Partners' Capital |  |  | 4.03% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.18%, 1/31/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,982,042 |
% of Partners' Capital |  |  | 4.02% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.20%, 2/07/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,977,646 |
% of Partners' Capital |  |  | 4.02% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.20%, 2/21/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,969,117 |
% of Partners' Capital |  |  | 4.02% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.38%, 3/07/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,957,479 |
% of Partners' Capital |  |  | 4.01% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.28%, 3/14/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,954,900 |
% of Partners' Capital |  |  | 4.01% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.33%, 3/21/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,949,528 |
% of Partners' Capital |  |  | 4.01% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.34%, 3/28/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,944,817 |
% of Partners' Capital |  |  | 4.01% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.37%, 4/04/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,939,421 |
% of Partners' Capital |  |  | 4.01% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.41%, 4/11/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,933,750 |
% of Partners' Capital |  |  | 4.01% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.42%, 4/18/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 5,000,000 |
Market Value |  |  | $ 4,964,408 |
% of Partners' Capital |  |  | 2.00% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.43%, 4/25/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,924,000 |
% of Partners' Capital |  |  | 4.00% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.47%, 5/09/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 15,000,000 |
Market Value |  |  | $ 14,870,133 |
% of Partners' Capital |  |  | 6.00% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.48%, 5/16/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,908,125 |
% of Partners' Capital |  |  | 3.99% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.50%, 5/23/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 20,000,000 |
Market Value |  |  | $ 19,805,539 |
% of Partners' Capital |  |  | 7.99% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.49%, 5/30/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,898,287 |
% of Partners' Capital |  |  | 3.99% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.51%, 6/06/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,892,750 |
% of Partners' Capital |  |  | 3.99% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.51%, 6/13/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,887,711 |
% of Partners' Capital |  |  | 3.99% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.49%, 6/20/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,883,833 |
% of Partners' Capital |  |  | 3.99% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.49%, 6/27/2019 [Member] |  |  |  |
Principal Amount |  |  | $ 10,000,000 |
Market Value |  |  | $ 9,879,050 |
% of Partners' Capital |  |  | 3.98% |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.05%, 1/02/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,999,438 |  |  |
% of Partners' Capital | 2.25% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.03%, 1/09/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,995,533 |  |  |
% of Partners' Capital | 2.25% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.01%, 1/16/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,991,729 |  |  |
% of Partners' Capital | 2.25% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.04%, 1/23/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,987,674 |  |  |
% of Partners' Capital | 2.25% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 2.02%, 1/30/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,983,905 |  |  |
% of Partners' Capital | 2.25% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.90%, 2/06/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,981,225 |  |  |
% of Partners' Capital | 2.25% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.87%, 2/13/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,977,843 |  |  |
% of Partners' Capital | 2.24% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.85%, 2/20/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,974,514 |  |  |
% of Partners' Capital | 2.24% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.85%, 2/27/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,971,025 |  |  |
% of Partners' Capital | 2.24% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.83%, 3/05/2020 [Member] |  |  |  |
Principal Amount | $ 20,000,000 |  |  |
Market Value | $ 19,935,413 |  |  |
% of Partners' Capital | 4.48% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.84%, 3/19/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,960,567 |  |  |
% of Partners' Capital | 2.24% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.88%, 3/26/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,956,083 |  |  |
% of Partners' Capital | 2.24% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.70%, 4/02/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,956,811 |  |  |
% of Partners' Capital | 2.24% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.64%, 4/09/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,955,175 |  |  |
% of Partners' Capital | 2.24% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.60%, 4/16/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,953,183 |  |  |
% of Partners' Capital | 2.24% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.60%, 4/23/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,950,092 |  |  |
% of Partners' Capital | 2.24% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.59%, 4/30/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,947,500 |  |  |
% of Partners' Capital | 2.24% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.54%, 5/07/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,946,201 |  |  |
% of Partners' Capital | 2.24% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.55%, 5/14/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,942,678 |  |  |
% of Partners' Capital | 2.24% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.55%, 5/21/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,939,879 |  |  |
% of Partners' Capital | 2.24% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.58%, 5/28/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,935,456 |  |  |
% of Partners' Capital | 2.23% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.53%, 6/04/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,934,556 |  |  |
% of Partners' Capital | 2.23% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.53%, 6/11/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,931,488 |  |  |
% of Partners' Capital | 2.23% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.54%, 6/18/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,928,175 |  |  |
% of Partners' Capital | 2.23% |  |  |
Cash Equivalents [Member] | United States Treasury Obligations [Member] | U.S. Treasury Bills, 1.57%, 6/25/2020 [Member] |  |  |  |
Principal Amount | $ 10,000,000 |  |  |
Market Value | $ 9,923,733 |  |  |
% of Partners' Capital | 2.23% |  |  |
Cash Equivalents [Member] | United States Contracts | Money Market Funds [Member] |  |  |  |
Market Value | $ 160,000,000 |  | $ 33,700,000 |
% of Partners' Capital | 35.99% |  | 13.59% |
Cash Equivalents [Member] | United States Contracts | Money Market Funds [Member] | Fidelity Investments Money Market Funds Government Portfolio [Member] |  |  |  |
Principal Amount | $ 115,000,000 |  | $ 2,500,000 |
Market Value | $ 115,000,000 |  | $ 2,500,000 |
% of Partners' Capital | 25.87% |  | 1.01% |
Cash Equivalents [Member] | United States Contracts | Money Market Funds [Member] | Goldman Sachs Financial Square Funds - Government Fund - Class FS [Member] |  |  |  |
Principal Amount | $ 25,000,000 |  | $ 31,200,000 |
Market Value | $ 25,000,000 |  | $ 31,200,000 |
% of Partners' Capital | 5.62% |  | 12.58% |
Cash Equivalents [Member] | United States Contracts | Money Market Funds [Member] | Morgan Stanley Institutional Liquidity Funds - Government Portfolio [Member] |  |  |  |
Principal Amount | $ 20,000,000 |  |  |
Market Value | $ 20,000,000 |  |  |
% of Partners' Capital | 4.50% |  |  |
[1] | Collateral amounted to $83,410,316 on open futures contracts.
[2] | Collateral amounted to $100,299,442 on open futures contracts.

X
- Definition Percentage of Partners Capital + References No definition available. + Details
Name: | ung_PercentageOfPartnersCapital
Namespace Prefix: | ung_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Unrealized gain (loss) on open commodity futures and cleared swap contracts. + References No definition available. + Details
Name: | ung_UnrealizedGainLossOnOpenCommodityFuturesAndClearedSwapContracts
Namespace Prefix: | ung_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Value of the investment at close of period. For schedules of investments that are categorized, the value would be aggregated by category. For investment in and advances to affiliates, if operations of any controlled companies are different in character from those of the company, group such affiliates within divisions and by type of activities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 210 -Section 50 -Paragraph 6 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=99383244&loc=d3e12121-115841 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-12C.Column C.7) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611225-123010 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 6 -Subparagraph (SX 210.12-14.Column E.2,3) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611322-123010 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-12.Column C.3,4) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611133-123010 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 5 -Subparagraph (SX 210.12-13.Column C.6) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611282-123010 + Details
Name: | us-gaap_InvestmentOwnedAtFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Balance held at close of period in number of contracts. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 6 -Subparagraph (SX 210.12-14.Column B) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611322-123010 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-12C.Column B) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611225-123010 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-12.Column B) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611133-123010 + Details
Name: | us-gaap_InvestmentOwnedBalanceContracts
Namespace Prefix: | us-gaap_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition For investments which are quantified by principal amount, the principle balance held at close of period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 210 -Section 50 -Paragraph 6 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=99383244&loc=d3e12121-115841 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-12C.Column B) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611225-123010 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 6 -Subparagraph (SX 210.12-14.Column B) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611322-123010 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-12.Column B) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611133-123010 + Details
Name: | us-gaap_InvestmentOwnedBalancePrincipalAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Nominal or face amount on the investment owned. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 20 -Section 10 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6438156&loc=d3e57880-113973 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 10 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6431724&loc=d3e32938-113948 + Details
Name: | us-gaap_InvestmentOwnedUnderlyingFaceAmountAtMarketValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_InvestmentTypeAxis=ung_OpenFuturesContractsLongMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_US
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_NYMEXNaturalGasFuturesNGFebruary2019ContractsExpiringJanuary2019Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_ICENaturalGasFuturesLD1HFebruary2019ContractsExpiringFebruary2019Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_CashEquivalentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CashAndCashEquivalentsAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsSixMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsSevenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillEightMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsNineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsTenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsElevenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsTwelveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsThirteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_USTreasuryBillFourteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFifteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsSixteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsSeventeenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsEighteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsNineteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsTwentyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsTwentyOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsTwentyTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsTwentyThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFourtyOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFourtyTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFourtyThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFourtyFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFourtyFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFourtySixMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFourtySevenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFourtyEightMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFourtyNineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFiftyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFiftyOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFiftyTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFiftyThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFiftyFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFiftyFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFiftySixMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFiftySevenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFiftyEightMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsFiftyNineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsSixtyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsSixtyOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsSixtyTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsSixtyThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsSixtyFourMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_UsTreasuryBillsSixtyFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CashAndCashEquivalentsAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_FidelityInvestmentsMoneyMarketFundsGovernmentPortfolioMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_GoldmanSachsFinancialSquareFundsGovernmentFundClassFsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ung_MorganStanleyInstitutionalLiquidityFundsGovernmentPortfolioMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |