Percentage investment held by the managing member or general partner of the limited liability company (LLC) or limited partnership (LP).

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- Definition

Total contributions made by each class of partners (i.e., general, limited and preferred partners).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
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- Definition

Total change in each class of partners' capital accounts during the year due to the sale of units. All partners include general, limited and preferred partners.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
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- Definition

The cash outflow for cost incurred directly with the issuance of an equity security.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
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-Paragraph 15
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- Definition

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.

+ References

No definition available.

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PARTNERS' EQUITY - ATM Equity Issuance Program (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
PARTNERS' EQUITY
Net proceeds from issuance of common units			$ 40
General Partner
PARTNERS' EQUITY
Net proceeds from issuance of common units			$ 1
TC PipeLines GP, Inc. \| General Partner
PARTNERS' EQUITY
Ownership interest in the Partnership (as a percent)	2.00%	2.00%	2.00%	2.00%
ATM Equity Issuance Program \| Common Units
PARTNERS' EQUITY
Units sold	0.0		0.7
Sales agent commissions			$ 0
Net proceeds from issuance of common units			39
ATM Equity Issuance Program \| TC PipeLines GP, Inc. \| General Partner
PARTNERS' EQUITY
Equity contribution			$ 1