Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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The average effective interest rate during the reporting period.

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DEBT AND CREDIT FACILITIES - Schedule of debt and credit facilities (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Jul. 23, 2020	Jun. 01, 2020
Debt Instrument [Line Items]
Debt, gross	$ 2,147	$ 2,012
Less: unamortized debt issuance costs and debt discount	7	9
Current portion of long-term debt	373	123
Debt, net	1,767	1,880
Revolving credit facility \| Senior Credit Facility due 2021
Debt Instrument [Line Items]
Debt, gross	$ 0	$ 0
Weighted average interest rate	0.00%	0.00%
Term loan \| 2013 Term Loan Facility due 2022
Debt Instrument [Line Items]
Debt, gross	$ 450	$ 450
Weighted average interest rate	2.03%	3.52%
Unsecured debt \| 4.65% Unsecured Senior Notes due 2021
Debt Instrument [Line Items]
Stated interest rate	4.65%
Debt, gross	$ 350	$ 350
Weighted average interest rate	4.65%	4.65%
Unsecured debt \| 4.375% Unsecured Senior Notes due 2025
Debt Instrument [Line Items]
Stated interest rate	4.375%
Debt, gross	$ 350	$ 350
Weighted average interest rate	4.375%	4.375%
Unsecured debt \| 3.90% Unsecured Senior Notes due 2027
Debt Instrument [Line Items]
Stated interest rate	3.90%
Debt, gross	$ 500	$ 500
Weighted average interest rate	3.90%	3.90%
GTN \| Secured debt \| 3.12% Series A Senior Notes due 2030
Debt Instrument [Line Items]
Stated interest rate	3.12%			3.12%
Debt, gross	$ 175	$ 0
Weighted average interest rate	3.12%	0.00%
GTN \| Unsecured debt \| 5.29% Unsecured Senior Notes due 2020
Debt Instrument [Line Items]
Stated interest rate	5.29%	5.29%		5.29%
Debt, gross	$ 0	$ 100
Weighted average interest rate	0.00%	5.29%
GTN \| Unsecured debt \| 5.69% Unsecured Senior Notes due 2035
Debt Instrument [Line Items]
Stated interest rate	5.69%
Debt, gross	$ 150	$ 150
Weighted average interest rate	5.69%	5.69%
PNGTS \| Secured debt \| Revolving Credit Facility due 2023
Debt Instrument [Line Items]
Debt, gross	$ 99	$ 39
Weighted average interest rate	2.02%	3.47%
Tuscarora \| Unsecured debt \| Unsecured Term Loan due 2021
Debt Instrument [Line Items]
Debt, gross	$ 23	$ 23	$ 23
Weighted average interest rate	2.13%	3.39%
North Baja \| Unsecured debt \| Unsecured Term Loan due 2021
Debt Instrument [Line Items]
Debt, gross	$ 50	$ 50
Weighted average interest rate	1.85%	3.34%