Equity Method Investments - Summary of Income Statement Data for Equity Method Investments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Schedule of Equity Method Investments [Line Items]
Total revenue	$ 131	$ 100
Operating income	65	5
Amberjack
Schedule of Equity Method Investments [Line Items]
Total Revenues	81
Total Operating Expenses	19
Operating Income	62
Net Income	62
Mars
Schedule of Equity Method Investments [Line Items]
Total Revenues	63	57
Total Operating Expenses	22	21
Operating Income	41	36
Net Income	41	36
Bengal
Schedule of Equity Method Investments [Line Items]
Total Revenues	18	15
Total Operating Expenses	7	4
Operating Income	11	11
Net Income	11	9
Poseidon
Schedule of Equity Method Investments [Line Items]
Total Revenues	31	29
Total Operating Expenses	9	9
Operating Income	22	20
Net Income	20	19
Proteus
Schedule of Equity Method Investments [Line Items]
Total Revenues	30	39
Total Operating Expenses	18	18
Operating Income	12	21
Net Income	$ 9	$ 19