Fair Value Measurements - Breakdown by Fair Value Hierarchy Category for Financial Instruments (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value [Abstract]
Assets from commodity derivative contracts		$ 72.3	$ 28.6
Liabilities from commodity derivative contracts		33.6	43.9
Carrying Value [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value [Abstract]
Assets from commodity derivative contracts	[1]	104.3	60.3
Liabilities from commodity derivative contracts	[1]	71.4	98.5
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
Cash and cash equivalents		219.8	137.2
Carrying Value [Member] | TRC Revolver [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
Long-term debt		435.0	435.0
Carrying Value [Member] | TRP Revolver [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
Long-term debt		380.0	20.0
Carrying Value [Member] | Partnership's Accounts Receivable Securitization Facility [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
Long-term debt		300.0	350.0
Carrying Value [Member] | Senior Unsecured Notes [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
Long-term debt		4,278.0	4,278.0
Carrying Value [Member] | Outrigger Permian Acquisition
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value [Abstract]
Additional cash paid in potential earn-out payment	[2]	373.0	317.0
Carrying Value [Member] | Targa Pipeline Partners LP [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value [Abstract]
Additional cash paid in potential earn-out payment	[3]	2.5	2.4
Fair Value [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value [Abstract]
Assets from commodity derivative contracts	[1]	104.3	60.3
Liabilities from commodity derivative contracts	[1]	71.4	98.5
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
Cash and cash equivalents		219.8	137.2
Fair Value [Member] | Level 1 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value [Abstract]
Assets from commodity derivative contracts	[1]	0.0	0.0
Liabilities from commodity derivative contracts	[1]	0.0	0.0
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
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 [Abstract]
Assets from commodity derivative contracts	[1]	103.9	58.8
Liabilities from commodity derivative contracts	[1]	67.7	93.3
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
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 [Abstract]
Assets from commodity derivative contracts	[1]	0.4	1.5
Liabilities from commodity derivative contracts	[1]	3.7	5.2
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
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 [Abstract]
Long-term debt		435.0	435.0
Fair Value [Member] | TRC Revolver [Member] | Level 1 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
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 [Abstract]
Long-term debt		435.0	435.0
Fair Value [Member] | TRC Revolver [Member] | Level 3 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
Long-term debt		0.0	0.0
Fair Value [Member] | TRP Revolver [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
Long-term debt		380.0	20.0
Fair Value [Member] | TRP Revolver [Member] | Level 1 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
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 [Abstract]
Long-term debt		380.0	20.0
Fair Value [Member] | TRP Revolver [Member] | Level 3 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
Long-term debt		0.0	0.0
Fair Value [Member] | Partnership's Accounts Receivable Securitization Facility [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
Long-term debt		300.0	350.0
Fair Value [Member] | Partnership's Accounts Receivable Securitization Facility [Member] | Level 1 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
Long-term debt		0.0	0.0
Fair Value [Member] | Partnership's Accounts Receivable Securitization Facility [Member] | Level 2 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
Long-term debt		300.0	350.0
Fair Value [Member] | Partnership's Accounts Receivable Securitization Facility [Member] | Level 3 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
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 [Abstract]
Long-term debt		4,257.0	4,362.4
Fair Value [Member] | Senior Unsecured Notes [Member] | Level 1 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
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 [Abstract]
Long-term debt		4,257.0	4,362.4
Fair Value [Member] | Senior Unsecured Notes [Member] | Level 3 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Carrying Value [Abstract]
Long-term debt		0.0	0.0
Fair Value [Member] | Outrigger Permian Acquisition
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value [Abstract]
Additional cash paid in potential earn-out payment	[2]	373.0	317.0
Fair Value [Member] | Outrigger Permian Acquisition | Level 1 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value [Abstract]
Additional cash paid in potential earn-out payment	[2]	0.0	0.0
Fair Value [Member] | Outrigger Permian Acquisition | Level 2 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value [Abstract]
Additional cash paid in potential earn-out payment	[2]	0.0	0.0
Fair Value [Member] | Outrigger Permian Acquisition | Level 3 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value [Abstract]
Additional cash paid in potential earn-out payment	[2]	373.0	317.0
Fair Value [Member] | Targa Pipeline Partners LP [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value [Abstract]
Additional cash paid in potential earn-out payment	[3]	2.5	2.4
Fair Value [Member] | Targa Pipeline Partners LP [Member] | Level 1 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value [Abstract]
Additional cash paid in potential earn-out payment	[3]	0.0	0.0
Fair Value [Member] | Targa Pipeline Partners LP [Member] | Level 2 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value [Abstract]
Additional cash paid in potential earn-out payment	[3]	0.0	0.0
Fair Value [Member] | Targa Pipeline Partners LP [Member] | Level 3 [Member]
Financial Instruments Recorded on Our Consolidated Balance Sheets at Fair Value [Abstract]
Additional cash paid in potential earn-out payment	[3]	$ 2.5	$ 2.4

[1] The fair value of derivative contracts in this table is presented on a different basis than the Consolidated Balance Sheets presentation as disclosed in Note 15 – Derivative Instruments and Hedging Activities. The above fair values reflect the total value of each derivative contract taken as a whole, whereas the Consolidated Balance Sheets presentation is based on the individual maturity dates of estimated future settlements. As such, an individual contract could have both an asset and liability position when segregated into its current and long-term portions for Consolidated Balance Sheets classification purposes.

[2] We have a contingent consideration liability related to the Permian Acquisition, which is carried at fair value. See Note 4 – Newly-Formed Joint Ventures and Acquisitions.

[3] We have a contingent consideration liability for TPL’s previous acquisition of a gas gathering system and related assets, which is carried at fair value.