Fair Value Measurements (Reconciliation Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 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)	$ 174	$ 182
Significant Unobservable Inputs (Level 3) [Member]
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	220	(159)
Purchases	2,239	3,248
Sales	(2,150)	(3,194)
Settlements	(66)	(69)
Transfers into Level 3	215	81
Transfers out of Level 3	(110)	(67)
Balance at end of period	1,945	1,302
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	1,486	1,322
Total increase (decrease) in unrealized gains included in cost of products sold	173	(228)
Purchases	2,239	3,248
Sales	(2,150)	(3,194)
Settlements	0	0
Transfers into Level 3	187	34
Transfers out of Level 3	(106)	(53)
Balance at end of period	1,829	1,129
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	111	140
Total increase (decrease) in unrealized gains included in cost of products sold	47	69
Purchases	0	0
Sales	0	0
Settlements	(66)	(69)
Transfers into Level 3	28	47
Transfers out of Level 3	(4)	(14)
Balance at end of period	$ 116	$ 173