Net Income per Unit (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended				6 Months Ended
	May 19, 2020	Feb. 19, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share Basic [Line Items]
Net Income (Loss) Attributable to Parent			$ 157	$ (128)	$ 55	$ 109	$ 29	$ 164
Incentive distribution rights	$ 18	$ 18	17		17		35	35
Distributions on nonvested phantom unit awards			$ 2		$ 2		$ 4	4
Limited partners’ interest in net income (loss)								$ 124
Weighted average common units outstanding:
Common - basic (in shares)			83,030,286		82,742,323		83,022,027	82,726,842
Common - diluted (in shares)			83,598,730		83,509,987		83,022,027	83,455,021
Common units - basic			$ 1.65		$ 0.44		$ (0.12)	$ 1.51
Common units - diluted			$ 1.64		$ 0.43		$ (0.12)	$ 1.50
Common Units [Member]
Earnings Per Share Basic [Line Items]
Limited partners’ interest in net income (loss)			$ 138		$ 36		$ (10)	$ 125
Weighted average common units outstanding:
Common - basic (in shares)			83,030,286		82,742,323		83,022,027	82,726,842
Common - equivalents (in shares)			568,444		767,664		0	728,179
Common - diluted (in shares)			83,598,730		83,509,987		83,022,027	83,455,021