EQUITY INVESTMENTS (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Apr. 30, 2006	Mar. 31, 2017	Mar. 31, 2016	May 01, 2017	Apr. 28, 2017	Apr. 18, 2017	Dec. 31, 2016
EQUITY INVESTMENTS
Equity Earnings		$ 43	$ 42
Equity Investments		1,062					$ 1,044
LIABILITIES AND PARTNERS' EQUITY
Current portion of long-term debt		23					23
Amount borrowed			195
Great Lakes
EQUITY INVESTMENTS
Total cash call issued to fund debt repayment		$ 9
Northern Border
EQUITY INVESTMENTS
Ownership interest (as a percent)		50.00%			50.00%
Equity Earnings		$ 19	18
Equity Investments		441					444
Amortization period of transaction fee	12 years
Transaction fee	$ 10
Additional ownership interest acquired (as a percent)	20.00%
Assets
Cash and cash equivalents		18					14
Other current assets		36					36
Plant, property and equipment, net		1,085					1,089
Other assets		15					14
Assets, total		1,154					1,153
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		44					38
Deferred credits and other		29					28
Long-term debt, including current maturities, net		430					430
Partners' equity
Partners' equity		653					659
Accumulated other comprehensive loss		(2)					(2)
Liabilities and Partners' Equity, total		1,154					1,153
Revenues (expenses)
Transmission revenues		74	74
Operating expenses		(17)	(16)
Depreciation		(15)	(15)
Financial charges and other		(4)	(6)
Net income		$ 38	37
Great Lakes
EQUITY INVESTMENTS
Ownership interest (as a percent)		46.45%		46.45%
Equity Earnings		$ 17	15
Equity Investments		489					474
Equity contribution		4	4
Assets
Current assets		86					66
Plant, property and equipment, net		708					714
Assets, total		794					780
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		31					40
Long-term debt, including current maturities, net		269					278
Partners' equity
Partners' equity		494					462
Liabilities and Partners' Equity, total		794					780
Revenues (expenses)
Transmission revenues		63	61
Operating expenses		(14)	(15)
Depreciation		(7)	(7)
Financial charges and other		(5)	(6)
Net income		$ 37	33
Portland Natural Gas Transmission System
EQUITY INVESTMENTS
Ownership interest (as a percent)		49.90%				49.90%
Equity Earnings		$ 7	9
Equity Investments		132					$ 126
Undistributed earnings		$ 0
Equity contribution			$ 193