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Fair Value Measurements - Changes in Fair Value of Financial Instruments Classified as Level 3 (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Changes in fair value of financial instruments classified as Level 3 in fair value hierarchy [Roll Forward]
Change in contingent considerations		$ (0.3)	$ 8.7	$ (8.8)
Contingent Consideration [Member]
Changes in fair value of financial instruments classified as Level 3 in fair value hierarchy [Roll Forward]
Balance, beginning of period		(2.3)
New Level 3 derivative instruments		0.0
Transfers out of Level 3	[1]	0.0
Balance, end of period		(2.0)	(2.3)
Targa Pipeline Partners LP [Member] | Contingent Consideration [Member]
Changes in fair value of financial instruments classified as Level 3 in fair value hierarchy [Roll Forward]
Change in contingent considerations		0.3
Commodity Derivative Contracts Asset/(Liability) [Member]
Changes in fair value of financial instruments classified as Level 3 in fair value hierarchy [Roll Forward]
Balance, beginning of period		(0.3)
New Level 3 derivative instruments		(0.2)
Transfers out of Level 3	[1]	0.3
Balance, end of period		$ (0.2)	$ (0.3)
[1] Transfers relate to long-term over-the-counter swaps for NGL products for which observable market prices became available for substantially their full term.

X

- Definition

Amount of increase (decrease) in the value of a contingent consideration liability, including, but not limited to, differences arising upon settlement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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-Section 50
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- Definition

Amount of transfers of financial instrument classified as a liability into level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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- Definition

Amount of transfers of financial instrument classified as a liability out of level 3 of the fair value hierarchy.

+ References

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-Name Accounting Standards Codification
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Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfers of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset) into level 3 of the fair value hierarchy.

+ References

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Amount of transfers of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset) out of level 3 of the fair value hierarchy.

+ References

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Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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