Fair Value Measurements (Reconciliation Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 243	$ 52	$ 523	$ 18
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	1,586	1,106	1,597	1,462
Total increase (decrease) in unrealized gains included in cost of products sold	313	69	861	139
Purchases	3,518	2,792	7,890	8,369
Sales	(3,282)	(2,655)	(8,264)	(8,526)
Settlements	(150)	(82)	(294)	(291)
Transfers into Level 3	273	82	358	148
Transfers out of Level 3	(242)	(98)	(132)	(87)
Balance at end of period	2,016	1,214	2,016	1,214
Significant Unobservable Inputs (Level 3) [Member] | Inventories Carried At Market [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	1,378	1,000	1,486	1,322
Total increase (decrease) in unrealized gains included in cost of products sold	183	15	559	(55)
Purchases	3,518	2,792	7,890	8,369
Sales	(3,282)	(2,655)	(8,264)	(8,526)
Settlements	0	0	0	0
Transfers into Level 3	235	37	235	37
Transfers out of Level 3	(233)	(95)	(107)	(53)
Balance at end of period	1,799	1,094	1,799	1,094
Significant Unobservable Inputs (Level 3) [Member] | Commodity Derivative Contracts Gains [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	208	106	111	140
Total increase (decrease) in unrealized gains included in cost of products sold	130	54	302	194
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	(150)	(82)	(294)	(291)
Transfers into Level 3	38	45	123	111
Transfers out of Level 3	(9)	(3)	(25)	(34)
Balance at end of period	$ 217	$ 120	$ 217	$ 120