Summarized Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 1,897		$ 1,529		$ 1,407		$ 1,593		$ 1,518		$ 903		$ 992		$ 891		$ 6,426	$ 4,304	$ 1,100
Income from operations	524		492		455		508		540		197		200		219		1,979	1,156	250
Net income	$ 351		$ 307		$ 281		$ 335		$ 374		$ 23		$ 46		$ 47		$ 1,274	$ 490	$ (171)
Net income (loss) per common unit—basic and diluted	$ 0.69	[1]	$ 0.60	[1]	$ 0.55	[1]	$ 0.67	[1]	$ 0.76	[1]	$ (1.10)	[1]	$ (3.71)	[1]	$ (0.80)	[1]	$ 2.51	$ (1.32)	$ (0.20)

[1] The sum of the quarterly net income (loss) per common unit may not equal the full year amount as the undistributed income and loss allocations and computations of the weighted average common units outstanding for basic and diluted common units outstanding for each quarter and the full year are performed independently.