Segment Information, Revenues by Product and Service and Reconciliation of Operating Margin to Net Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Revenue from External Customer [Line Items]
Sale of commodities	$ 1,402.2us-gaap_RevenueMineralSales	$ 2,085.1us-gaap_RevenueMineralSales
Fees from midstream services	277.5us-gaap_NaturalGasMidstreamRevenue	209.6us-gaap_NaturalGasMidstreamRevenue
Total revenues	1,679.7	2,294.7
Reconciliation of operating margin to net income [Abstract]
Operating margin	300.0trgp_OperatingMargin	275.3trgp_OperatingMargin
Depreciation and amortization expense	(119.6)	(79.6)
General and administrative expense	(42.6)us-gaap_GeneralAndAdministrativeExpense	(38.0)us-gaap_GeneralAndAdministrativeExpense
Interest expense, net	(55.0)us-gaap_InterestIncomeExpenseNet	(33.9)us-gaap_InterestIncomeExpenseNet
Other, net	(33.0)us-gaap_OtherNonrecurringIncomeExpense	5.6us-gaap_OtherNonrecurringIncomeExpense
Income tax expense	(15.2)us-gaap_IncomeTaxExpenseBenefit	(22.5)us-gaap_IncomeTaxExpenseBenefit
Net income	34.6	106.9
Natural Gas Sales [Member]
Revenue from External Customer [Line Items]
Sale of commodities	302.1	391.8
NGL Sales [Member]
Revenue from External Customer [Line Items]
Sale of commodities	1,030.7	1,650.9
Condensate Sales [Member]
Revenue from External Customer [Line Items]
Sale of commodities	21.3	28.4
Petroleum Products [Member]
Revenue from External Customer [Line Items]
Sale of commodities	26.4	20.1
Derivative Settlements [Member]
Revenue from External Customer [Line Items]
Sale of commodities	21.7	(6.1)
Fractionating and Treating Fees [Member]
Revenue from External Customer [Line Items]
Fees from midstream services	49.8	46.5
Storage, Terminaling, Transportation and Export Fees [Member]
Revenue from External Customer [Line Items]
Fees from midstream services	136.2	101.2
Gathering and Processing Fees [Member]
Revenue from External Customer [Line Items]
Fees from midstream services	68.4	42.6
Other [Member]
Revenue from External Customer [Line Items]
Fees from midstream services	$ 23.1	$ 19.3

Revenues reduced by product purchases and operating expenses.

No definition available.

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The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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Revenue related to midstream and downstream gas activities. May include the following: gathering from wells, processing to remove impurities, storage, transmission, and the sale of natural gas and related products.

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The aggregate total of expenses of managing and administering the affairs of an entity, including affiliates of the reporting entity, which are not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Midstream refers to those gas industry activities that fall between exploration and production (upstream) and refining and marketing (downstream). It may be applied to the gathering, processing, transmission and storage of natural gas; including the treating of natural gas to remove impurities, along with the sale of by-products such as residue gas, natural gas liquids and condensate.

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Aggregate revenue from the sale of minerals and related products, and from rendering services such as exploration, development, mining, processing and providing mining support activities.

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