Accounts Receivable (Accounts Receivable) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: Allowance for doubtful accounts	$ (148)	$ (130)
Accounts receivable, net	519	553
Retail And Wholesale [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	592	608
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 75	$ 75