Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accounting Policies [Abstract]
Motor fuel and sales taxes	$ 64	$ 100	$ 144	$ 194
Accounts Receivable, Allowance for Credit Loss	$ 16		$ 16