Related Party Debt - Additional Information (Details) - USD ($) $ in Millions					3 Months Ended		9 Months Ended
	Jul. 31, 2018	Feb. 06, 2018	Mar. 01, 2017	Nov. 03, 2014	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2018
Line Of Credit Facility [Line Items]
Interest and fee expenses					$ 20	$ 10
Interest paid					20	11
Borrowing capacity					2,990			$ 2,990
Repayments of debt					0	$ 973
Level 2
Line Of Credit Facility [Line Items]
Long-term debt, carrying value					2,094			2,094
Long-term debt, fair value					2,131			2,099
Five Year Fixed Facility
Line Of Credit Facility [Line Items]
Debt instrument term						5 years
Five Year Revolver due December 2022
Line Of Credit Facility [Line Items]
Borrowing capacity					1,000			1,000
Debt instrument term						5 years
Repayments of debt		$ 726
Five Year Fixed Facility
Line Of Credit Facility [Line Items]
Borrowing capacity					$ 600			$ 600
Debt instrument term				5 years
Repayments of debt		$ 247
Seven Year Fixed Facility | Shell Treasury Center West Inc | Fixed Facility | STCW
Line Of Credit Facility [Line Items]
Debt instrument term	7 years
Five Year Fixed Facility | Shell Treasury Center West Inc
Line Of Credit Facility [Line Items]
Debt instrument term							5 years
Five Year Fixed Facility | Shell Treasury Center West Inc | Fixed Facility
Line Of Credit Facility [Line Items]
Debt instrument term			5 years