Related Party Debt - Schedule of Consolidated Related Party Debt Obligations (Details) - USD ($) $ in Millions		3 Months Ended
	Nov. 03, 2014	Mar. 31, 2018	Mar. 31, 2019	Dec. 31, 2018
Line Of Credit Facility [Line Items]
Outstanding Balance			$ 2,091	$ 2,091
Unamortized debt issuance costs			(3)	(3)
Total Capacity			2,990	2,990
Available Capacity			896	896
Seven Year Fixed Facility
Line Of Credit Facility [Line Items]
Outstanding Balance			600	600
Total Capacity			600	600
Available Capacity			0	0
Five Year Revolver due July 2023
Line Of Credit Facility [Line Items]
Outstanding Balance			494	494
Total Capacity			760	760
Available Capacity			266	266
Five Year Revolver due December 2022
Line Of Credit Facility [Line Items]
Debt instrument term		5 years
Five Year Fixed Facility
Line Of Credit Facility [Line Items]
Debt instrument term	5 years
Outstanding Balance			600	600
Total Capacity			600	600
Available Capacity			0	0
Zydeco Revolver
Line Of Credit Facility [Line Items]
Outstanding Balance			0	0
Total Capacity			30	30
Available Capacity			30	30
Five Year Revolver due December 2022
Line Of Credit Facility [Line Items]
Debt instrument term		5 years
Outstanding Balance			400	400
Total Capacity			1,000	1,000
Available Capacity			$ 600	$ 600