Represents the number of customers with a credit risk concentration risk as of the date of the financial statements.

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- Definition

Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity.

+ References

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- Definition

Face (par) amount of debt instrument at time of issuance.

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- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and elected not to be offset.

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- Definition

Average fixed interest rate related to the group of interest rate derivatives.

+ References

No definition available.

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- Definition

The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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- Definition

The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

+ References

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- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and elected not to be offset.

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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.

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No definition available.

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FAIR VALUE MEASUREMENTS - Interest Rate Swaps (Details)	12 Months Ended
FAIR VALUE MEASUREMENTS - Interest Rate Swaps (Details)	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jul. 01, 2013 USD ($)
Accounts receivable
Interest rate derivatives
Maximum counterparty credit exposure	$ 0
Number of credit risk customers \| item	1
Term loan \| TC PipeLines, LP 2013 Term Loan Facility due 2018
Interest rate derivatives
Amount of facility				$ 500,000,000
Interest rate swaps \| Term loan \| TC PipeLines, LP 2013 Term Loan Facility due 2018
Interest rate derivatives
Weighted average fixed interest rate (as a percent)	2.31%
Hedges of cash flows \| Interest rate swaps
Interest rate derivatives
Change in fair value of interest rate derivative instruments recognized in other comprehensive income (loss)	$ 2,000,000	$ 0	$ (1,000,000)
Hedges of cash flows \| Interest rate swaps \| Financial charges and other.
Interest rate derivatives
Net realized loss related to the interest rate swaps	3,000,000	2,000,000	$ 2,000,000
Hedges of cash flows \| Interest rate swaps \| Recurring fair value measurement \| Level 2
Interest rate derivatives
Fair value of derivative asset, gross	1,000,000
Fair value of derivative liability, gross	1,000,000
Fair value of derivatives, net	$ 0	1,000,000
Designated as hedge \| Interest rate swaps \| Recurring fair value measurement \| Level 2
Interest rate derivatives
Fair value of derivative liability, gross		$ 1,000,000