Net Income Per Limited Partner Unit (Schedule of Earnings Per unit of our Limited Partners) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Limited Partners' Capital Account [Line Items]
Net income	$ 255	$ 233	$ 481	$ 431
Less:
Distributions declared	209	186	418	370
Distributions less than net income	46	47	63	61
General Partner
Limited Partners' Capital Account [Line Items]
Net income		71		140
Less:
Distributions declared	0	70	0	139
Preferred Units | Limited Partner
Limited Partners' Capital Account [Line Items]
Net income	9		19	19
Less:
Distributions declared	9	9	19	19
Common Units | Limited Partner
Limited Partners' Capital Account [Line Items]
Net income	246	153	462	272
Less:
Distributions declared	$ 200	$ 107	$ 399	$ 212