Related Party Transactions - Retail Vehicle Acquisitions (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Vehicle inventory	$ 2,285		$ 2,285		$ 1,036
Cost of goods sold, related to vehicles acquired	2,957	$ 1,282	7,648	$ 3,210
Used Vehicles | DriveTime Automotive Group, Inc. | Related Party
Related Party Transaction [Line Items]
Vehicle inventory	47		47
Used Vehicle Sales | DriveTime Automotive Group, Inc. | Related Party
Related Party Transaction [Line Items]
Cost of goods sold, related to vehicles acquired	$ 17		$ 19