Related Party Debt - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Line Of Credit Facility [Line Items]
Interest and fee expenses	$ 23	$ 22	$ 47	$ 41
Interest paid	24	$ 20	49	$ 39
Long-term debt, carrying value	2,694		2,694		$ 2,694
Long-term debt, fair value	2,891		2,891		2,825
Borrowing capacity	3,590		3,590		3,590
Ten Year Fixed Facility | Revolving Credit Facility
Line Of Credit Facility [Line Items]
Borrowing capacity	600		600		600
Seven Year Fixed Facility | Revolving Credit Facility
Line Of Credit Facility [Line Items]
Borrowing capacity	600		600		600
Five Year Revolver due July 2023 | Revolving Credit Facility
Line Of Credit Facility [Line Items]
Borrowing capacity	760		760		760
Five Year Fixed Facility | Revolving Credit Facility
Line Of Credit Facility [Line Items]
Borrowing capacity	$ 600		$ 600		$ 600