CONSOLIDATED STATEMENT OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Generated from Operations
Net income (loss)	$ 298.0	$ (165.0)	$ 263.0
Depreciation	78.0	97.0	97.0
Impairment of long lived assets (Note 7)		537.0
Impairment of goodwill (Note 4)		59.0
Amortization of debt issue costs reported as interest expense (Note 13)	2.0	2.0	2.0
Amortization of realized loss on derivative instrument (Note 20)		1.0	1.0
Equity earnings from equity investments (Note 5)	(160.0)	(173.0)	(124.0)
Distributions received from operating activities of equity investments (Note 5)	200.0	188.0	140.0
Change in other long-term liabilities	(1.0)	(2.0)
Equity allowance for funds used during construction	(2.0)	(1.0)	(1.0)
Change in operating working capital (Note 16)	(3.0)	(3.0)	(2.0)
Cash generated from operations	412.0	540.0	376.0
Investing Activities
Distribution received from return of investment (Note 5)	58.0	10.0	5.0
Capital expenditures	(75.0)	(40.0)	(29.0)
Other	(1.0)	4.0	1.0
Investing activities	(32.0)	(35.0)	(761.0)
Financing Activities
Distributions paid (Note 15)	(189.0)	(218.0)	(284.0)
Distributions paid to non-controlling interests	(22.0)	(14.0)	(5.0)
Distributions paid to former parent of PNGTS			(1.0)
Common unit issuance, net (Note 11)		40.0	176.0
Long-term debt issued, net of discount (Note 9)	30.0	219.0	802.0
Long-term debt repaid (Note 9)	(136.0)	(516.0)	(310.0)
Debt issuance costs		(1.0)	(2.0)
Financing activities	(330.0)	(505.0)	354.0
Increase/(decrease) in cash and cash equivalents	50.0		(31.0)
Cash and cash equivalents, beginning of year	33.0	33.0	64.0
Cash and cash equivalents, end of year	83.0	33.0	33.0
Interest payments paid	87.0	94.0	79.0
State income taxes paid	2.0	1.0	2.0
Supplemental information about non-cash investing and financing activities
Accrued capital expenditures	12.0	7.0	9.0
Class B Units
Financing Activities
Distributions paid to Class B units (Notes 11 and 15)	(13.0)	(15.0)	(22.0)
Portland Natural Gas Transmission System And Iroquois Acquisition
Investing Activities
Investment of interests			(646.0)
Great Lakes
Cash Generated from Operations
Equity earnings from equity investments (Note 5)	(51.0)	(59.0)	(31.0)
Investing Activities
Investment of interests	(10.0)	(9.0)	(9.0)
Iroquois
Cash Generated from Operations
Equity earnings from equity investments (Note 5)	(40.0)	(46.0)	(26.0)
Investing Activities
Investment of interests	(4.0)
Distribution received from return of investment (Note 5)	8.0	10.0	5.0
Northern Border
Cash Generated from Operations
Equity earnings from equity investments (Note 5)	(69.0)	$ (68.0)	(67.0)
Investing Activities
Investment of interests			$ (83.0)
Distribution received from return of investment (Note 5)	$ 50.0