Derivatives and Risk Management Activities - Interest Rate Risk Hedging (Details) - Cash Flow Hedge $ in Millions	6 Months Ended
Jun. 30, 2025 USD ($) contract
8 forward starting interest rate swaps (30-year), 3.09%
Interest Rate Risk Hedging
Number of interest rate derivatives \| contract	8
Term of derivative contract	30 years
Notional amount of derivatives \| $	$ 200
Average rate locked (as a percent)	3.09%
4 forward starting interest rate swaps (30-year), 3.76%
Interest Rate Risk Hedging
Number of interest rate derivatives \| contract	4
Term of derivative contract	30 years
Notional amount of derivatives \| $	$ 100
Average rate locked (as a percent)	3.76%
4 Treasury Locks (10-year) 4.00%
Interest Rate Risk Hedging
Number of interest rate derivatives \| contract	4
Term of derivative contract	10 years
Notional amount of derivatives \| $	$ 100
Average rate locked (as a percent)	4.00%

Average fixed interest rate related to the group of interest rate derivatives.

No definition available.

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

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 181
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480401/815-10-55-181

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

+ Details

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

- Definition

Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_InterestRateDerivativesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of interest rate derivative instruments held by the entity at the reporting date.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

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Namespace Prefix:
Data Type:	na
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- Details

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Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=pagp_FourForwardStartingThirtyYearInterestRateSwaps3.76PercentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=pagp_FourTreasuryLocksTenYearInterestRateSwaps4.00PercentMember
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Data Type:	na
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