Supplemental Data (Summary of Accounts Receivable, Net) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Supplemental Data (Millions of dollars) [Abstract]
From customers	$ 2,132	$ 2,131
Other	153	181
Less allowance for doubtful accounts and sales discounts	(50)	(49)
Total	$ 2,235	$ 2,263