EQUITY INVESTMENTS (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended
	Apr. 30, 2006	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jul. 18, 2016	Jan. 01, 2016	Dec. 31, 2015
EQUITY INVESTMENTS
Equity Earnings		$ 22		$ 15	$ 64	$ 46
Equity Investments		$ 1,047			$ 1,047				$ 965
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		$ 16		15	$ 34	34
Equity Investments		455			455				480
Amortization period of transaction fee	12 years
Transaction fee	$ 10
Additional ownership interest acquired (as a percent)	20.00%
Assets
Cash and cash equivalents		16			16				27
Other current assets		34			34				33
Plant, property and equipment, net		1,108			1,108				1,124
Other assets		15			15				16
Assets, total		1,173			1,173				1,200
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		40			40				39
Deferred credits and other		27			27				26
Long-term debt, including current maturities, net		429			429				409
Partners' equity
Partners' equity		679			679				728
Accumulated other comprehensive loss		(2)			(2)				(2)
Liabilities and Partners' Equity, total		1,173			1,173				1,200
Revenues (expenses)
Transmission revenues		70		69	144	144
Operating expenses		(18)		(18)	(35)	(34)
Depreciation		(15)		(14)	(29)	(29)
Financial charges and other		(6)		(6)	(11)	(11)
Net income		$ 31		31	$ 69	70
Great Lakes
EQUITY INVESTMENTS
Ownership interest (as a percent)		46.45%	46.45%		46.45%
Equity Earnings		$ 4			$ 19	12
Equity Investments		472			472				485
Equity contribution			$ 4		4	4
Assets
Current assets		53			53				86
Plant, property and equipment, net		721			721				727
Assets, total		774			774				813
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		29			29				31
Long-term debt, including current maturities, net		288			288				297
Partners' equity
Partners' equity		457			457				485
Liabilities and Partners' Equity, total		774			774				813
Revenues (expenses)
Transmission revenues		36		28	97	76
Operating expenses		(15)		(14)	(30)	(25)
Depreciation		(7)		(7)	(14)	(14)
Financial charges and other		(5)		(6)	(11)	(12)
Net income		$ 9		$ 1	$ 42	$ 25
Portland Natural Gas Transmission System
EQUITY INVESTMENTS
Ownership interest (as a percent)		49.90%			49.90%		49.90%	49.90%
Equity Earnings		$ 2			$ 11
Equity Investments		120			120
Undistributed earnings		$ 0			0
Equity contribution					$ 193
ASU 2015-03, Interest - Imputation of Interest | Adjustment | Northern Border
Assets
Other assets									(2)
LIABILITIES AND PARTNERS' EQUITY
Long-term debt, including current maturities, net									$ (2)