CONSOLIDATED STATEMENTS OF INCOME shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares
Transmission revenues	$ 357	$ 344	$ 336
Equity earnings (Note 4)	116	97	88
Impairment of equity-method investment (Note 4)		199
Operation and maintenance expenses	(50)	(53)	(54)
Property taxes	(19)	(19)	(21)
General and administrative	(7)	(9)	(9)
Depreciation	(86)	(85)	(86)
Financial charges and other (Note 11)	(67)	(56)	(50)
Net income	244	20	204
Net income attributable to non-controlling interests		7	32
Net income attributable to controlling interests	244	13	172
Net income (loss) attributable to controlling interest allocation (Note 12)
General Partner	11	3	4
Net income attributable to controlling interests	244	13	172
Common units
Net income (loss) attributable to controlling interest allocation (Note 12)
Limited partners	$ 211	$ (2)	$ 168
Net income (loss) per common unit (Note 12) - basic (in dollars per unit) | $ / shares	$ 3.21	$ (0.03)	$ 2.67
Net income (loss) per common unit (Note 12) - diluted (in dollars per unit) | $ / shares	$ 3.21	$ (0.03)	$ 2.67
Weighted average common units outstanding - basic (in units) | shares	65.7	63.9	62.7
Weighted average common units outstanding - diluted (in units) | shares	65.7	63.9	62.7
Common units outstanding, end of year (in units) | shares	67.4	64.3	63.6
Class B units
Net income (loss) attributable to controlling interest allocation (Note 12)
Limited partners	$ 22	$ 12