Debt Instruments - Floor Plan Facility (Details) - USD ($)				1 Months Ended
	Jul. 01, 2021	Mar. 01, 2021	Oct. 01, 2020	Nov. 30, 2019	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Line of credit, outstanding					$ 455,000,000	$ 40,000,000
Held in restricted cash					107,000,000	$ 28,000,000	$ 22,000,000	$ 42,000,000
Floor Plan Facility | Line of Credit
Line of Credit Facility [Line Items]
Outstanding balance, days held in inventory threshold				180 days
Outstanding balance, held in inventory, percentage of original principal amount due				10.00%
Outstanding balance, held in inventory, original principal amount, threshold				50.00%
Outstanding balance, held in inventory, wholesale value, threshold				50.00%
Deposit required under floor plan facility, percentage of principal balance				7.50%
Line of credit facility, maximum borrowing capacity	$ 1,750,000,000		$ 1,250,000,000		$ 1,750,000,000
Interest rate					2.62%	3.87%
Line of credit, outstanding					$ 455,000,000	$ 40,000,000
Line of credit facility, remaining borrowing capacity					1,300,000,000	1,200,000,000
Held in restricted cash					$ 34,000,000	$ 3,000,000
Floor Plan Facility | Line of Credit | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate		2.65%	3.15%
Floor Plan Facility | Line of Credit | Prime Rate
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	(0.50%)