Net Income Per Limited Partner Unit (Schedule of Earnings Per unit of our Limited Partners) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Limited Partners' Capital Account [Line Items]
Net income	$ 226	$ 198
Less:
Distributions declared	209	184
Distributions less than net income	17	14
General Partner
Limited Partners' Capital Account [Line Items]
Net income		69
Less:
Distributions declared	0	69
Preferred Units | Limited Partner
Limited Partners' Capital Account [Line Items]
Net income	10	10
Less:
Distributions declared	10	10
Common Units | Limited Partner
Limited Partners' Capital Account [Line Items]
Net income	216	119
Less:
Distributions declared	$ 199	$ 105