Fair Value Measurements (Reconciliation Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 210	$ 174
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	1,670	1,597
Total increase (decrease) in unrealized gains included in cost of products sold	117	220
Purchases	2,689	2,239
Sales	(2,824)	(2,150)
Settlements	(103)	(66)
Transfers into Level 3	320	215
Transfers out of Level 3	(146)	(110)
Balance at end of period	1,723	1,945
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	1,515	1,486
Total increase (decrease) in unrealized gains included in cost of products sold	(27)	173
Purchases	2,689	2,239
Sales	(2,824)	(2,150)
Settlements	0	0
Transfers into Level 3	297	187
Transfers out of Level 3	(139)	(106)
Balance at end of period	1,511	1,829
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	155	111
Total increase (decrease) in unrealized gains included in cost of products sold	144	47
Purchases	0	0
Sales	0	0
Settlements	(103)	(66)
Transfers into Level 3	23	28
Transfers out of Level 3	(7)	(4)
Balance at end of period	$ 212	$ 116