Equity-Indexed Compensation Plans (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended	92 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015
Grant Date Fair Value of Outstanding AAP Management Units:
Equity-indexed compensation expense	$ 19	$ 34
AAP Management Units
Reserved for Future Grants
Reserved for future grants, beginning balance (in units)	3.0
Reserved for future grants, ending balance (in units)	3.0		3.0
Outstanding
Outstanding at the beginning of the period (in units)	49.1
Outstanding at the ending of the period (in units)	49.1		49.1
Outstanding Units Earned
Outstanding Units Earned, beginning balance (in units)	47.8
Earned (in units)	0.3
Outstanding Units Earned, end balance (in units)	48.1		48.1
Grant Date Fair Value of Outstanding AAP Management Units:
Grant Date Fair Value of Outstanding AAP Management Units, beginning balance	64
Grant Date Fair Value of Outstanding AAP Management Units, ending balance	64		64
Equity-indexed compensation expense	$ 1		$ 56

Name:	pagp_AAPManagementUnitActivityRollForward
Namespace Prefix:	pagp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	pagp_GrantDateFairValueOfOutstandingAAPManagementUnitsRollForward
Namespace Prefix:	pagp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	pagp_OutstandingUnitsEarnedRollForward
Namespace Prefix:	pagp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	pagp_OutstandingUnitsRollForward
Namespace Prefix:	pagp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of shares outstanding/issued under a share-based award plan which have become earned during the reporting period as certain performance conditions have been met giving the grantee the right to receive quarterly distributions.

+ References

No definition available.

+ Details

Name:	pagp_ShareBasedCompensationArrangementByShareBasedPaymentAwardEarnedInPeriod
Namespace Prefix:	pagp_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The grant date fair value of outstanding units.

+ References

No definition available.

+ Details

Name:	pagp_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedGrantDateFairValue
Namespace Prefix:	pagp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The number of outstanding awards on non-stock option plans for which the employer has issued equity instruments to an employee, including both employees who have and who have not yet satisfied service or performance criteria necessary to gain title to distributions to the shares.

+ References

No definition available.

+ Details

Name:	pagp_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstanding
Namespace Prefix:	pagp_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of authorized units that have not yet been granted/issued and are reserved for future grants.

+ References

No definition available.

+ Details

Name:	pagp_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReservedForFutureGrants
Namespace Prefix:	pagp_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of outstanding awards on non-stock option plans for which the employer has issued equity instruments to an employee and the units issued have been earned as required performance conditions have been met, giving the employee the right to receive quarterly distributions.

+ References

No definition available.

+ Details

Name:	pagp_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsUnitsEarnedOutstanding
Namespace Prefix:	pagp_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 14.F)

-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_PlanNameAxis=pagp_EquityBasedCompensationPlanAAPManagementUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: