Series A Preferred Units (Rollforward of Redeemable Preferred Units) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	[1]
Redeemable Noncontrolling Interest [Line Items]
Balance at December 31, 2019	$ 968
Distributions to unitholders and general partner	(1,445)	$ (1,038)
Balance at June 30, 2020	968
Series A Convertible Preferred Units
Redeemable Noncontrolling Interest [Line Items]
Balance at December 31, 2019	968
Net income allocated	41
Distributions to unitholders and general partner	(41)
Balance at June 30, 2020	$ 968

[1] Financial information for the six months ended June 30, 2019 has been retrospectively adjusted for the acquisition of ANDX. See Notes 1 and 3.