Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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Period Type:	duration

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The effective interest rate at the end of the reporting period.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount to which the maximum borrowing capacity under the credit facility could be expanded without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

No definition available.

+ Details

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Namespace Prefix:	wgp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percent of offering price to public.

+ References

No definition available.

+ Details

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Namespace Prefix:	wgp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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Debt and Interest Expense - Additional Information (Details) - USD ($)		9 Months Ended
	Feb. 16, 2018	Sep. 30, 2018	Sep. 30, 2017	Aug. 31, 2018	Mar. 31, 2018	Feb. 25, 2014
Revolving Credit Facility [Member] \| WGP RCF [Member]
Debt Instrument [Line Items]
Facility, maximum borrowing capacity	$ 35,000,000.0
Facility, expiration date	Mar. 14, 2019
Facility, outstanding borrowings		$ 28,000,000
Facility, available borrowing capacity		$ 7,000,000
Facility, interest rate at period end		4.25%	3.24%
Facility, fee rate		0.30%	0.30%
Western Gas Partners, LP [Member] \| 4.750% Senior Notes due 2028 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		4.75%
Offering percent				99.818%
Effective interest rate				4.885%
Western Gas Partners, LP [Member] \| 5.500% Senior Notes due 2048 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		5.50%
Offering percent				98.912%
Effective interest rate				5.652%
Western Gas Partners, LP [Member] \| 4.500% Senior Notes due 2028 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		4.50%
Offering percent					99.435%
Effective interest rate					4.682%
Western Gas Partners, LP [Member] \| 5.300% Senior Notes due 2048 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		5.30%
Offering percent					99.169%
Effective interest rate					5.431%
Western Gas Partners, LP [Member] \| Revolving Credit Facility [Member] \| WES RCF [Member]
Debt Instrument [Line Items]
Facility, maximum borrowing capacity	$ 1,500,000,000.0					$ 1,200,000,000.0
Facility, expiration date	Feb. 15, 2023
Facility, outstanding borrowings		$ 0
Facility, available borrowing capacity		$ 1,495,400,000
Facility, interest rate at period end		3.56%	2.54%
Facility, fee rate		0.20%	0.20%
Facility, expandable maximum borrowing capacity	$ 2,000,000,000
Outstanding letters of credit		$ 4,600,000
Western Gas Partners, LP [Member] \| Revolving Credit Facility [Member] \| WES RCF [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Facility, fee rate		0.125%
Western Gas Partners, LP [Member] \| Revolving Credit Facility [Member] \| WES RCF [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Facility, fee rate		0.25%
Western Gas Partners, LP [Member] \| Revolving Credit Facility [Member] \| WES RCF [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Alternate Base Rate [Member]
Debt Instrument [Line Items]
Applicable margin added		1.00%
Western Gas Partners, LP [Member] \| Revolving Credit Facility [Member] \| WES RCF [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Applicable margin added		1.00%
Western Gas Partners, LP [Member] \| Revolving Credit Facility [Member] \| WES RCF [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Applicable margin added		1.50%
Western Gas Partners, LP [Member] \| Revolving Credit Facility [Member] \| WES RCF [Member] \| Percentage Above Federal Funds Effective Rate [Member] \| Alternate Base Rate [Member]
Debt Instrument [Line Items]
Applicable margin added		0.50%
Western Gas Partners, LP [Member] \| Revolving Credit Facility [Member] \| WES RCF [Member] \| Base Rate [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Applicable margin added		0.00%
Western Gas Partners, LP [Member] \| Revolving Credit Facility [Member] \| WES RCF [Member] \| Base Rate [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Applicable margin added		0.50%