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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	$ 165	$ 243	$ 656	$ 523
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	1,547	1,586	1,670	1,597
Total increase (decrease) in unrealized gains included in cost of products sold	118	313	467	861
Purchases	2,772	3,518	8,118	7,890
Sales	(2,643)	(3,282)	(8,425)	(8,264)
Settlements	(106)	(150)	(346)	(294)
Transfers into Level 3	234	273	267	358
Transfers out of Level 3	(331)	(242)	(160)	(132)
Balance at end of period	1,591	2,016	1,591	2,016
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	1,388	1,378	1,515	1,486
Total increase (decrease) in unrealized gains included in cost of products sold	27	183	148	559
Purchases	2,772	3,518	8,118	7,890
Sales	(2,643)	(3,282)	(8,425)	(8,264)
Settlements	0	0	0	0
Transfers into Level 3	213	235	213	235
Transfers out of Level 3	(327)	(233)	(139)	(107)
Balance at end of period	1,430	1,799	1,430	1,799
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	159	208	155	111
Total increase (decrease) in unrealized gains included in cost of products sold	91	130	319	302
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	(106)	(150)	(346)	(294)
Transfers into Level 3	21	38	54	123
Transfers out of Level 3	(4)	(9)	(21)	(25)
Balance at end of period	$ 161	$ 217	$ 161	$ 217