Fair Value Measurements - Breakdown by Fair Value Hierarchy Category for Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value:
Assets from commodity derivative contracts	$ 21.1	$ 46.2
Liabilities from commodity derivative contracts	521.5	67.6
Carrying Value [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value:
Assets from commodity derivative contracts	96.1	134.8
Liabilities from commodity derivative contracts	623.5	186.0
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Cash and cash equivalents	228.6	242.8
Carrying Value [Member] \| TRC Revolver [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	0.0	555.0
Carrying Value [Member] \| TRP Revolver [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	0.0	280.0
Carrying Value [Member] \| Partnership's Securitization Facility [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	340.0	350.0
Carrying Value [Member] \| Senior Unsecured Notes [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	6,465.7	6,585.4
Fair Value [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value:
Assets from commodity derivative contracts	96.1	134.8
Liabilities from commodity derivative contracts	623.5	186.0
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Cash and cash equivalents	228.6	242.8
Fair Value [Member] \| Level 1 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value:
Assets from commodity derivative contracts	0.0	0.0
Liabilities from commodity derivative contracts	0.0	0.0
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Cash and cash equivalents	0.0	0.0
Fair Value [Member] \| Level 2 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value:
Assets from commodity derivative contracts	96.1	134.8
Liabilities from commodity derivative contracts	623.4	185.8
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Cash and cash equivalents	0.0	0.0
Fair Value [Member] \| Level 3 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value:
Assets from commodity derivative contracts	0.0	0.0
Liabilities from commodity derivative contracts	0.1	0.2
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Cash and cash equivalents	0.0	0.0
Fair Value [Member] \| TRC Revolver [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	0.0	555.0
Fair Value [Member] \| TRC Revolver [Member] \| Level 1 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	0.0	0.0
Fair Value [Member] \| TRC Revolver [Member] \| Level 2 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	0.0	555.0
Fair Value [Member] \| TRC Revolver [Member] \| Level 3 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	0.0	0.0
Fair Value [Member] \| TRP Revolver [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	0.0	280.0
Fair Value [Member] \| TRP Revolver [Member] \| Level 1 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	0.0	0.0
Fair Value [Member] \| TRP Revolver [Member] \| Level 2 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	0.0	280.0
Fair Value [Member] \| TRP Revolver [Member] \| Level 3 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	0.0	0.0
Fair Value [Member] \| Partnership's Securitization Facility [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	340.0	350.0
Fair Value [Member] \| Partnership's Securitization Facility [Member] \| Level 1 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	0.0	0.0
Fair Value [Member] \| Partnership's Securitization Facility [Member] \| Level 2 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	340.0	350.0
Fair Value [Member] \| Partnership's Securitization Facility [Member] \| Level 3 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	0.0	0.0
Fair Value [Member] \| Senior Unsecured Notes [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	6,909.8	7,036.8
Fair Value [Member] \| Senior Unsecured Notes [Member] \| Level 1 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	0.0	0.0
Fair Value [Member] \| Senior Unsecured Notes [Member] \| Level 2 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	6,909.8	7,036.8
Fair Value [Member] \| Senior Unsecured Notes [Member] \| Level 3 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value:
Long-term debt	$ 0.0	$ 0.0

Financial instruments recorded on our consolidated balance sheets at carrying value.

No definition available.

Name:	trgp_FinancialInstrumentsRecordedOnOurConsolidatedBalanceSheetsAtCarryingValueAbstract
Namespace Prefix:	trgp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Financial instruments recorded on our consolidated balance sheets at fair value.

+ References

No definition available.

+ Details

Name:	trgp_FinancialInstrumentsRecordedOnOurConsolidatedBalanceSheetsAtFairValueAbstract
Namespace Prefix:	trgp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

No definition available.

+ Details

Name:	us-gaap_CashAndCashEquivalentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69C
-URI http://asc.fasb.org/extlink&oid=123466577&loc=SL123495737-112612

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69B
-URI http://asc.fasb.org/extlink&oid=123466577&loc=SL123495735-112612

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=123594938&loc=d3e13433-108611

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1D
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611

+ Details

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

- Definition

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=123594938&loc=d3e13433-108611

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

Name:	us-gaap_DerivativeAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=123594938&loc=d3e13433-108611

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313

+ Details

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

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_CarryingReportedAmountFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=trgp_TRCRevolverMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=trgp_TRPRevolverMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=trgp_PartnershipsSecuritizationFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_UnsecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: