Fair Value Measurements (Reconciliation Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$ 1,678	$ 1,670
Total increase (decrease) in unrealized gains included in cost of products sold	1,084	744
Purchases	14,185	10,833
Sales	(13,852)	(11,167)
Settlements	(257)	(421)
Transfers into Level 3	360	182
Transfers out of Level 3	(156)	(163)
Balance at end of period	3,042	1,678
Inventories Carried At Market [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	1,477	1,515
Total increase (decrease) in unrealized gains included in cost of products sold	146	327
Purchases	14,185	10,833
Sales	(13,852)	(11,167)
Transfers into Level 3	290	108
Transfers out of Level 3	(63)	(139)
Balance at end of period	2,183	1,477
Commodity Derivative Contracts Gains [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	201	155
Total increase (decrease) in unrealized gains included in cost of products sold	938	417
Settlements	(257)	(421)
Transfers into Level 3	70	74
Transfers out of Level 3	(93)	(24)
Balance at end of period	$ 859	$ 201