EQUITY INVESTMENTS (Details) - USD ($) $ in Millions			3 Months Ended
	May 01, 2019	Apr. 24, 2019	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
EQUITY INVESTMENTS
Equity Earnings			$ 54	$ 59
Equity Investments			1,196		$ 1,196
Equity contribution			5	4
LIABILITIES AND PARTNERS' EQUITY
Current portion of long-term debt (Note 7)			36		36
Distributions from Equity Investments
Distributions received from equity investments			58	45
Distributions from equity investments			56	43
Return on investment distribution classified as investing activities			2	2
Great Lakes
EQUITY INVESTMENTS
Total cash call issued to fund debt repayment			$ 11
Iroquois
EQUITY INVESTMENTS
Ownership interest (as a percent)	49.34%		49.34%
Distributions from Equity Investments
Distributions from equity investments	$ 14		$ 14	14
Return on investment distribution classified as investing activities	$ 2		$ 2	2
Limited partners, Distribution declared		$ 28
Northern Border
EQUITY INVESTMENTS
Ownership interest (as a percent)			50.00%
Equity Earnings			$ 21	17
Equity Investments			489		497
ASSETS
Cash and cash equivalents			14		10
Other current assets			38		36
Property, plant and equipment, net			1,023		1,037
Other assets			13		13
Assets, total			1,088		1,096
LIABILITIES AND PARTNERS' EQUITY
Current liabilities			41		34
Deferred credits and other			35		35
Net long-term debt, including current maturities			264		264
Current portion of long-term debt (Note 7)			0		0
Partners' capital			749		764
Accumulated other comprehensive loss			(1)		(1)
Liabilities and Partners' Equity, total			1,088		1,096
Revenues (expenses)
Transmission revenues			81	72
Operating expenses			(20)	(19)
Depreciation			(15)	(15)
Financial charges and other			(4)	(4)
Net income			$ 42	34
Great Lakes
EQUITY INVESTMENTS
Ownership interest (as a percent)			46.45%
Equity Earnings			$ 20	24
Equity Investments			498		489
Equity contribution			5	4
ASSETS
Current assets			86		75
Property, plant and equipment, net			685		689
Assets, total			771		764
LIABILITIES AND PARTNERS' EQUITY
Current liabilities			25		26
Net long-term debt, including current maturities			229		240
Current portion of long-term debt (Note 7)			21		21
Other non-current liabilities			4		4
Partners' capital			513		494
Liabilities and Partners' Equity, total			771		764
Revenues (expenses)
Transmission revenues			72	81
Operating expenses			(16)	(17)
Depreciation			(8)	(8)
Financial charges and other			(4)	(4)
Net income			$ 44	52
Iroquois
EQUITY INVESTMENTS
Ownership interest (as a percent)			49.34%
Equity Earnings			$ 13	18
Equity Investments			209		210
ASSETS
Cash and cash equivalents			84		80
Other current assets			30		32
Property, plant and equipment, net			576		581
Other assets			16		8
Assets, total			706		701
LIABILITIES AND PARTNERS' EQUITY
Current liabilities			19		19
Net long-term debt, including current maturities			325		325
Current portion of long-term debt (Note 7)			146		146
Other non-current liabilities			20		14
Partners' capital			342		343
Liabilities and Partners' Equity, total			706		$ 701
Revenues (expenses)
Transmission revenues			52	60
Operating expenses			(15)	(14)
Depreciation			(7)	(7)
Financial charges and other			(3)	(4)
Net income			$ 27	$ 35