Fair Value Measurements (Reconciliation Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$ 1,597	$ 1,462
Total increase (decrease) in unrealized gains included in cost of products sold	1,026	219
Purchases	11,153	11,236
Sales	(11,728)	(11,231)
Settlements	(468)	(369)
Transfers into Level 3	237	377
Transfers out of Level 3	(147)	(97)
Balance at end of period	1,670	1,597
Inventories Carried At Market [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	1,486	1,322
Total increase (decrease) in unrealized gains included in cost of products sold	631	(29)
Purchases	11,153	11,236
Sales	(11,728)	(11,231)
Transfers into Level 3	80	241
Transfers out of Level 3	(107)	(53)
Balance at end of period	1,515	1,486
Commodity Derivative Contracts Gains [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	111	140
Total increase (decrease) in unrealized gains included in cost of products sold	395	248
Settlements	(468)	(369)
Transfers into Level 3	157	136
Transfers out of Level 3	(40)	(44)
Balance at end of period	$ 155	$ 111