CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY - USD ($) shares in Millions, $ in Millions		Limited Partners Common units GTN	Limited Partners Common units Bison	Limited Partners Common units Portland Natural Gas Transmission System	Limited Partners Common units ATM Equity Issuance Program	Limited Partners Common units	Limited Partners Class B units	General Partner GTN	General Partner Portland Natural Gas Transmission System	General Partner ATM Equity Issuance Program	General Partner	Accumulated Other Comprehensive Loss	[1]	Class B units	Non-controlling interests GTN	Non-controlling interests Bison	Non-controlling interests	GTN	Bison	Portland Natural Gas Transmission System	ATM Equity Issuance Program	Total
Partners' Equity at beginning of year at Dec. 31, 2013						$ 1,322					$ 28	$ (1)					$ 440					$ 1,789
Partners' Equity at beginning of year (in units) at Dec. 31, 2013						62.3
Increase (Decrease) in Partners' Equity
Net income (loss)						$ 168					4						32					204
Other Comprehensive Income (Loss), net												(1)										(1)
Equity Issuance, net (Note 9); Issuance of Units (Note 6 and 9)					$ 71					$ 2											$ 73
Equity Issuance, net (Note 9); Issuance of Units (Note 6 and 9) (in units)					1.3
Acquisition of interest (Note 6)			$ (29)													$ (188)			$ (217)
Distributions						(207)					(5)						(50)					(262)
Partners' Equity at end of year at Dec. 31, 2014						$ 1,325					29	(2)					234					1,586
Partners' Equity at end of year (in units) at Dec. 31, 2014						63.6
Increase (Decrease) in Partners' Equity
Net income (loss)						$ (2)	$ 12				3						7					20
Equity Issuance, net (Note 9); Issuance of Units (Note 6 and 9)					$ 43		$ 95			1				$ 95							44
Equity Issuance, net (Note 9); Issuance of Units (Note 6 and 9) (in units)					0.7		1.9
Acquisition of interest (Note 6)		$ (124)						$ (3)							$ (232)			$ (359)
Equity Contribution (Note 6)											2											2
Distributions						(221)					(7)						$ (9)					(237)
Partners' Equity at end of year at Dec. 31, 2015						$ 1,021	$ 107				25	(2)										1,151
Partners' Equity at end of year (in units) at Dec. 31, 2015						64.3	1.9
Increase (Decrease) in Partners' Equity
Net income (loss)						$ 211	$ 22				11											244
Other Comprehensive Income (Loss), net												$ 2										2
Equity Issuance, net (Note 9); Issuance of Units (Note 6 and 9)					$ 82					$ 2											$ 84
Equity Issuance, net (Note 9); Issuance of Units (Note 6 and 9) (in units)					1.5
Common unit issuance subject to rescission, net (Note 9)						$ 81					2											83
Common unit issuance subject to rescission, net (Note 9) (in units)						1.6
Reclassification of common unit issuance subject to rescission, net (Note 9)	[2]					$ (81)					(2)											(83)
Acquisition of interest (Note 6)				$ (72)					$ (1)											$ (73)
Distributions						(240)	(12)				(10)											(262)
Partners' Equity at end of year at Dec. 31, 2016						$ 1,002	$ 117				$ 27											$ 1,146
Partners' Equity at end of year (in units) at Dec. 31, 2016						67.4	1.9

[1] Losses related to cash flow hedges reported in Accumulated Other Comprehensive Loss and expected to be reclassified to net income in the next 12 months are estimated to be nil. These estimates assume constant interest rates over time; however, the amounts reclassified will vary based on actual value of interest rates at the date of settlement.

[2] These units are treated as outstanding for financial reporting purposes.