PROPERTY, PLANT AND EQUIPMENT - Summary (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
PROPERTY, PLANT AND EQUIPMENT
Cost	$ 2,997	$ 2,715
Accumulated Depreciation	(1,250)	(1,187)
Net Book Value	1,747	1,528
Pipeline
PROPERTY, PLANT AND EQUIPMENT
Cost	1,910	1,907
Accumulated Depreciation	(982)	(929)
Net Book Value	928	978
Compression
PROPERTY, PLANT AND EQUIPMENT
Cost	730	584
Accumulated Depreciation	(210)	(202)
Net Book Value	520	382
Metering and other
PROPERTY, PLANT AND EQUIPMENT
Cost	208	180
Accumulated Depreciation	(58)	(56)
Net Book Value	150	124
Payment to acquire commercial system	26
Metering and other \| Great Lakes Gas Transmissions Limited Partnership
PROPERTY, PLANT AND EQUIPMENT
Payment to acquire commercial system	12
Construction in progress
PROPERTY, PLANT AND EQUIPMENT
Cost	149	44
Net Book Value	$ 149	$ 44

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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