Earnings per Unit - Basic and Diluted Earnings Per Unit (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Allocation of net income among partner interests:
Net income attributable to common unitholders	$ 163	$ 257	$ 387	$ 503
Class A common units
Allocation of net income among partner interests:
Net income attributable to common unitholders	$ 106	$ 142	$ 250	$ 277
Denominator - basic and diluted partnership units:
Total weighted average basic and diluted units outstanding (in shares)	202	202	202	202
Earnings per unit - basic and diluted:
Earnings per unit - basic and diluted (in usd per share)	$ 0.52	$ 0.70	$ 1.24	$ 1.37
Partnership exchangeable units
Allocation of net income among partner interests:
Net income attributable to common unitholders	$ 57	$ 115	$ 137	$ 226
Denominator - basic and diluted partnership units:
Total weighted average basic and diluted units outstanding (in shares)	164	207	165	207
Earnings per unit - basic and diluted:
Earnings per unit - basic and diluted (in usd per share)	$ 0.35	$ 0.55	$ 0.83	$ 1.09