Earnings Per Limited Partner Unit (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income		$ 44	$ 124	$ 149	$ 247
Net (loss) income attributable to noncontrolling interest		0	0	(7)	1
Series A Preferred Unit distributions		9	9	18	18
General partner interest in net income		0	0	0	0
Net Income Attributable to Common Units (Note 5)		$ 35	$ 115	$ 138	$ 228
Phantom units
Basic weighted average number of outstanding
Basic weighted average number of outstanding		2	1	2	1
Common Unit [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income Attributable to Common Units (Note 5)		$ 35	$ 115	$ 138	$ 228
Dilutive effect of Series A Preferred Unit distributions		0	0	18	0
Diluted net income		$ 35	$ 115	$ 156	$ 228
Basic earnings per unit
Basic earnings per unit		$ 0.08	$ 0.26	$ 0.32	$ 0.52
Basic weighted average number of outstanding
Basic weighted average number of outstanding	[1]	437	437	437	436
Dilutive effect of Series A Preferred Units (in units)		0	0	79	0
Diluted weighted average number of outstanding units		437	437	516	436
Diluted earnings per unit		$ 0.08	$ 0.26	$ 0.30	$ 0.52

[1] Basic weighted average number of outstanding common units includes approximately two million time-based phantom units for the three and six months ended June 30, 2020, and one million time-based phantom units for the three and six months ended June 30, 2019.