EQUITY INVESTMENTS (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Apr. 30, 2006	Mar. 31, 2016	Mar. 31, 2015	Jan. 01, 2016	Dec. 31, 2015
Equity Investments
Equity Earnings		$ 42	$ 31
Equity Investments		1,083			$ 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%
Equity Earnings		$ 18	20
Equity Investments		476			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		35			27
Other current assets		34			33
Plant, property and equipment, net		1,117			1,124
Other assets		15			16
Assets, total		1,201			1,200
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		46			39
Deferred credits and other		26			26
Long-term debt, including current maturities, net		409			409
Partners' equity
Partners' equity		722			728
Accumulated other comprehensive loss		(2)			(2)
Liabilities and Partners' Equity, total		1,201			1,200
Revenues (expenses)
Transmission revenues		74	75
Operating expenses		(16)	(16)
Depreciation		(15)	(15)
Financial charges and other		(6)	(5)
Net income		$ 37	39
Great Lakes
Equity Investments
Ownership interest (as a percent)		46.45%
Equity Earnings		$ 15	11
Equity Investments		485			485
Equity contribution		4	4
Assets
Current assets		73			86
Plant, property and equipment, net		725			727
Assets, total		798			813
LIABILITIES AND PARTNERS' EQUITY
Current liabilities		25			31
Long-term debt, including current maturities, net		288			297
Partners' equity
Partners' equity		485			485
Liabilities and Partners' Equity, total		798			813
Revenues (expenses)
Transmission revenues		61	48
Operating expenses		(15)	(11)
Depreciation		(7)	(7)
Financial charges and other		(6)	(6)
Net income		$ 33	$ 24
Portland Natural Gas Transmission System
Equity Investments
Ownership interest (as a percent)		49.90%		49.90%
Equity Earnings		$ 9
Equity Investments		122
Undistributed earnings		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)