Fair Value Measurements - Additional Information (Details) $ in Millions	Sep. 30, 2018 USD ($) Swap
Fair Value Disclosures [Abstract]
Derivative financial instruments, fair value, net	$ 175.8
Derivative fair value of net liability if commodity price increases by 10 percent	281.7
Derivative fair value of net liability if commodity price decreases by 10 percent	$ 69.9
Number of natural gas basis swaps categorized as Level 3 \| Swap	16

Fair value as of the balance sheet date of the assets less the liabilities of a derivative or group of derivatives if the commodity price decreases by 10 percent.

No definition available.

+ Details

Name:	trgp_DerivativeFairValueOfAssetLiabilityNetIfCommodityPriceDecreasesBy10Percent
Namespace Prefix:	trgp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value as of the balance sheet date of the assets less the liabilities of a derivative or group of derivatives if the commodity price increases by 10 percent.

+ References

No definition available.

+ Details

Name:	trgp_DerivativeFairValueOfAssetLiabilityNetIfCommodityPriceIncreasesBy10Percent
Namespace Prefix:	trgp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This line item represents the number of natural gas basis swaps categorized as Level 3 by the entity.

+ References

No definition available.

+ Details

Name:	trgp_NumberOfNaturalGasBasisSwapsCategorizedAsLevel3
Namespace Prefix:	trgp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: 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=109250915&loc=d3e13433-108611

+ Details

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

- References

No definition available.

+ Details

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