CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Transmission revenues	$ 95	$ 93	$ 196	$ 206
Equity earnings (Note 5)	29	30	84	84
Operation and maintenance expenses	(16)	(17)	(32)	(33)
Property taxes	(7)	(6)	(13)	(13)
General and administrative	(2)	(2)	(3)	(4)
Depreciation and amortization	(19)	(19)	(39)	(39)
Financial charges and other (Note 15)	(18)	(21)	(37)	(43)
Net income before taxes	62	58	156	158
Income taxes	(1)	(1)	(1)	(1)
Net income	61	57	155	157
Net income attributable to non-controlling interest	4	2	10	9
Net income attributable to controlling interests	57	55	145	148
Net income attributable to controlling interest allocation (Note 9)
Common units	56	54	142	145
General Partner	1	1	3	3
Net income attributable to controlling interests	$ 57	$ 55	$ 145	$ 148
Net income per common unit (Note 9) - basic and diluted (in dollars per unit)	$ 0.78	$ 0.75	$ 1.99	$ 2.03
Weighted average common units outstanding — basic and diluted (millions)	71.3	71.3	71.3	71.3
Common units outstanding, end of period (millions)	71.3	71.3	71.3	71.3