Revenue Recognition - Contract Balances (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Movement in Deferred Revenue [Roll Forward]
Deferred revenue, beginning balance	$ 8
Deferred revenue, ending balance	1
Third Parties
Movement in Deferred Revenue [Roll Forward]
Deferred revenue, beginning balance	8
Additions	0
Reductions	(7)
Deferred revenue, ending balance	1
Related Parties
Movement in Deferred Revenue [Roll Forward]
Deferred revenue, beginning balance	3
Additions	0
Reductions	(2)
Deferred revenue, ending balance	$ 1