Amount of additional cash paid to acquire the entity on closing, subject to certain post closing adjustments.

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The percentage of acquisition cost of a business combination allocated to the noncurrent portion of the long-term debt assumed from the acquired entity.

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The item represents the difference, if any, between the amount at which purchase price is paid over recorded equity investments accounted for under the equity method of accounting.

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Represents the equity method investment recorded at TransCanada's carrying value.

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Represents the price per unit of units sold in a public offering.

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Amount of potential cash payments that could result from the contingent consideration arrangement.

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Amount of cash paid to acquire the entity.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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This element represents the aggregate cost of investments accounted for under the equity method of accounting.

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The number of units or percentage investment held by the managing member or general partner of the LLC or LP.

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- Definition

Amount borrowed under the credit facility as of the balance sheet date.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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The minimum amount the entity agreed to spend under the long-term purchase commitment.

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Monetary value of the issuance of new units of limited partnership interest in a public offering, net of offering costs. This is a parenthetical disclosure.

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The number of units sold in a public offering of each class of partners' capital account. Units represent shares of ownership of the general, limited, and preferred partners.

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Cash outflow representing an adjustment to the purchase price of a previous acquisition.

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The cash inflow from the capital received in cash from a partner in a partnership during the period.

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-Name Statement of Financial Accounting Standard (FAS)

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ACQUISITIONS (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended			1 Months Ended	9 Months Ended	1 Months Ended		1 Months Ended			1 Months Ended					1 Months Ended	3 Months Ended	9 Months Ended
	May 31, 2011	Mar. 31, 2011 Yuma Lateral Asset Acquisition North Baja Pipeline, LLC	Jun. 29, 2010 Yuma Lateral Asset Acquisition North Baja Pipeline, LLC	May 31, 2011 General Partner GTN and Bison	Sep. 30, 2011 General Partner GTN and Bison	May 31, 2011 GTN and Bison	May 03, 2011 GTN and Bison	May 31, 2011 GTN and Bison GTN	May 03, 2011 GTN and Bison GTN	May 03, 2011 GTN and Bison Bison	May 31, 2011 GTN and Bison Bison Capital Commitment	May 03, 2011 GTN and Bison Bridge loan facility	May 03, 2011 GTN and Bison Senior revolving credit facility	May 03, 2011 GTN	May 03, 2011 Bison	May 31, 2011 General Partner	Sep. 30, 2011 General Partner	Sep. 30, 2011 General Partner	May 03, 2011 Bridge loan facility	Sep. 30, 2011 Senior revolving credit facility	Jul. 13, 2011 Senior revolving credit facility
Asset acquisition
Interest acquired by the Partnership (as a percent)								25.00%
Purchase price							$ 605.0		$ 405.0	$ 200.0
Payment to be made to TransCanada if other shippers contracted for services			2.4
Additional payment to TransCanada		2.4
Acquired debt									81.3
Percentage of acquired debt (as a percent)									25.00%
Future capital commitment to complete the Bison pipeline											9.1
Additional cash paid on closing							23.5
Cash in hand							14.5			538.1
Number of common units issued	7,245,000					7,245,000
Price per common unit issued (in dollars per unit)	$ 47.58					$ 47.58
Net proceeds from issuance of common units	330.9					330.9
Outstanding balance												61.0	125.0						61.0
Maximum borrowing capacity												400.0	250.0						400.0	500.0	250.0
Contribution by General Partners				6.7
General partner ownership interest in the partnership (as a percent)					2.00%											2.00%	2.00%	2.00%
Excess of purchase price over recorded equity investments							130.9
Equity investments recorded at TransCanada's carrying value														$ 245.9	$ 161.3