Inventories (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
LIFO inventory amount	$ 3,331	$ 3,123
Estimated excess of current replacement cost over LIFO cost of inventories	4,300	2,900
LIFO inventory liquidations	$ 0	$ 0	$ 0