Fair Value Measurements (Reconciliation Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	$ 280	$ 105	$ 491	$ 280
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	1,723	1,945	1,670	1,597
Total increase (decrease) in unrealized gains included in cost of products sold	321	114	444	441
Purchases	2,657	2,133	5,346	4,372
Sales	(2,958)	(2,832)	(5,782)	(4,982)
Settlements	(137)	(78)	(240)	(144)
Transfers into Level 3	242	397	265	425
Transfers out of Level 3	(301)	(93)	(156)	(123)
Balance at end of period	1,547	1,586	1,547	1,586
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	1,511	1,829	1,515	1,486
Total increase (decrease) in unrealized gains included in cost of products sold	237	(11)	216	269
Purchases	2,657	2,133	5,346	4,372
Sales	(2,958)	(2,832)	(5,782)	(4,982)
Settlements	0	0	0	0
Transfers into Level 3	232	340	232	340
Transfers out of Level 3	(291)	(81)	(139)	(107)
Balance at end of period	1,388	1,378	1,388	1,378
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	212	116	155	111
Total increase (decrease) in unrealized gains included in cost of products sold	84	125	228	172
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	(137)	(78)	(240)	(144)
Transfers into Level 3	10	57	33	85
Transfers out of Level 3	(10)	(12)	(17)	(16)
Balance at end of period	$ 159	$ 208	$ 159	$ 208