CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Transmission revenues	$ 101	$ 113
Equity earnings (Note 5)	55	54
Operation and maintenance expenses	(16)	(16)
Property taxes	(6)	(7)
General and administrative	(1)	(2)
Depreciation and amortization	(20)	(20)
Financial charges and other (Note 15)	(19)	(22)
Net income before taxes	94	100
Income taxes	0	0
Net income	94	100
Net income attributable to non-controlling interest	6	7
Net income attributable to controlling interests	88	93
Net income attributable to controlling interest allocation (Note 9)
Common units	86	91
General Partner	2	2
Net income attributable to controlling interests	$ 88	$ 93
Net income per common unit (Note 9) - basic and diluted (in dollars per unit)	$ 1.21	$ 1.28
Weighted average common units outstanding — basic and diluted (millions)	71.3	71.3
Common units outstanding, end of period (millions)	71.3	71.3