NET INCOME PER COMMON UNIT - Schedule of net income per common unit (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net income per common unit
Net income attributable to controlling interests	$ 65	$ 56	$ 210	$ 204
Net income attributable to the Class B units	0	(1)	0	(1)
Net income attributable to the General Partner and common units	65	55	210	203
Net income attributable to the General Partner	(1)	(1)	(4)	(4)
Net income attributable to common units	$ 64	$ 54	$ 206	$ 199
Weighted average common units outstanding - basic and diluted (in shares)	71.3	71.3	71.3	71.3
Net income per common unit - basic and diluted (in dollars per share)	$ 0.90	$ 0.76	$ 2.89	$ 2.79