LONG-TERM DEBT - Schedule of Activity and Summary of Principal Repayments (Details) CAD in Millions, $ in Millions	12 Months Ended
Dec. 31, 2015 CAD	Dec. 31, 2015 USD ($)	Dec. 31, 2014 CAD	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 31,584		CAD 24,757
Less: Current portion of Long-term debt	2,547		1,797
Long-term Debt, Excluding Current Maturities	29,037		22,960
Repayments of Long-term Debt [Abstract]
2016	2,547
2017	2,150
2018	3,379
2019	1,228
2020	1,801
TRANSCANADA PIPELINES LIMITED
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	26,685		20,916
TRANSCANADA PIPELINES LIMITED \| Debentures, Maturity Dates Between 2015 and 2020
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 599		CAD 749
Interest Rate	10.70%	10.70%	10.90%	10.90%
TRANSCANADA PIPELINES LIMITED \| Debentures, Maturity Date of 2021
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 554	$ 400	CAD 464	$ 400
Interest Rate	9.90%	9.90%	9.90%	9.90%
TRANSCANADA PIPELINES LIMITED \| Medium-Term Notes
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 5,192		CAD 4,048
Interest Rate	5.30%	5.30%	5.70%	5.70%
TRANSCANADA PIPELINES LIMITED \| Senior Unsecured Notes
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 20,340	$ 14,723	CAD 15,655	$ 13,526
Interest Rate	4.80%	4.80%	5.00%	5.00%
NOVA GAS TRANSMISSION LTD.
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 1,151		CAD 1,099
NOVA GAS TRANSMISSION LTD. \| Debentures and Notes, Maturity Dates between 2016 and 2024
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 325		CAD 325
Interest Rate	11.50%	11.50%	11.50%	11.50%
NOVA GAS TRANSMISSION LTD. \| Debentures and Notes, Maturity Date of 2023
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 277	$ 200	CAD 232	$ 200
Interest Rate	7.90%	7.90%	7.90%	7.90%
NOVA GAS TRANSMISSION LTD. \| Medium-Term Notes, Maturity between 2025 and 2030
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 504		CAD 504
Interest Rate	7.40%	7.40%	7.40%	7.40%
NOVA GAS TRANSMISSION LTD. \| Medium-Term Notes, Maturity Date of 2026
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 45	$ 33	CAD 38	$ 33
Interest Rate	7.50%	7.50%	7.50%	7.50%
NOVA GAS TRANSMISSION LTD. \| Debentures and Notes
Debt Instrument [Line Items]
Long-term debt issued with retraction provision	CAD 225
NOVA GAS TRANSMISSION LTD. \| Debentures and Notes \| Maximum
Debt Instrument [Line Items]
Redemption price, percentage	8.00%
ANR PIPELINE COMPANY \| Senior Unsecured Notes
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 598	$ 432	CAD 502	$ 432
Interest Rate	8.90%	8.90%	8.90%	8.90%
GAS TRANSMISSION NORTHWEST LLC
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 450		CAD 377
GAS TRANSMISSION NORTHWEST LLC \| Senior Unsecured Notes
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 346	$ 250	CAD 377	$ 325
Interest Rate	5.60%	5.60%	5.50%	5.50%
GAS TRANSMISSION NORTHWEST LLC \| Unsecured Term Loan
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 104	$ 75
Interest Rate	1.40%	1.40%
TC PIPELINES, LP
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 2,171		CAD 1,368
TC PIPELINES, LP \| Senior Unsecured Notes
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 967	$ 698	CAD 405	$ 350
Interest Rate	4.70%	4.70%	4.70%	4.70%
TC PIPELINES, LP \| Unsecured Term Loan
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 235	$ 170
Interest Rate	1.60%	1.60%
TC PIPELINES, LP \| Unsecured Loan
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 277	$ 200	CAD 383	$ 330
Interest Rate	1.60%	1.60%	1.40%	1.40%
TC PIPELINES, LP \| Unsecured Term Loan Facility
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 692	$ 500	CAD 580	$ 500
Interest Rate	1.60%	1.60%	1.40%	1.40%
GREAT LAKES GAS TRANSMISSION LIMITED PARTNERSHIP \| Senior Unsecured Notes
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 411	$ 297	CAD 367	$ 316
Interest Rate	7.80%	7.80%	7.80%	7.80%
TUSCARORA GAS TRANSMISSION COMPANY \| Secured Debt
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 22	$ 16	CAD 23	$ 20
Interest Rate	4.00%	4.00%	4.00%	4.00%
PORTLAND NATURAL GAS TRANSMISSION SYSTEM \| Secured Debt
Debt Instrument [Line Items]
Current and Long-Term Debt, Outstanding December 31	CAD 96	$ 69	CAD 105	$ 90
Interest Rate	6.10%	6.10%	6.10%	6.10%

Long-Term Debt Issued with Retraction Provision

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Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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Amount of long-term debt, after unamortized discount or premium, scheduled to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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