CONSOLIDATED STATEMENTS OF INCOME (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Transmission revenues	$ 99	$ 93	$ 295	$ 299
Equity earnings (Note 5)	39	31	123	115
Operation and maintenance expenses	(16)	(18)	(48)	(51)
Property taxes	(7)	(6)	(20)	(19)
General and administrative	(1)	(2)	(4)	(6)
Depreciation and amortization	(29)	(19)	(68)	(58)
Financial charges and other (Note 15)	(17)	(20)	(54)	(63)
Net income before taxes	68	59	224	217
Income taxes	0	0	(1)	(1)
Net income	68	59	223	216
Net income attributable to non-controlling interest	3	3	13	12
Net income attributable to controlling interests	65	56	210	204
Net income attributable to controlling interest allocation (Note 9)
Common units	64	54	206	199
General Partner	1	1	4	4
Class B units	0	1	0	1
Net income attributable to controlling interests	$ 65	$ 56	$ 210	$ 204
Net income per common unit (Note 9) - basic and diluted (in dollars per share)	$ 0.90	$ 0.76	$ 2.89	$ 2.79
Weighted average common units outstanding - basic and diluted (in shares)	71.3	71.3	71.3	71.3
Common units outstanding, end of period (in shares)	71.3	71.3	71.3	71.3