Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accounting Policies [Abstract]
Motor fuel and sales taxes	$ 82	$ 101	$ 226	$ 295
Accounts Receivable, Allowance for Credit Loss	$ 16		$ 16