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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 52	$ 22	$ 18	$ 36
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	1,106	1,252	1,462	1,247
Total increase (decrease) in unrealized gains included in cost of products sold	69	(21)	139	(39)
Purchases	2,792	2,523	8,369	7,565
Sales	(2,655)	(2,529)	(8,526)	(7,272)
Settlements	(82)	(85)	(291)	(302)
Transfers into Level 3	82	272	148	338
Transfers out of Level 3	(98)	(44)	(87)	(169)
Balance at end of period	1,214	1,368	1,214	1,368
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	1,000	1,099	1,322	1,004
Total increase (decrease) in unrealized gains included in cost of products sold	15	(97)	(55)	(210)
Purchases	2,792	2,523	8,369	7,565
Sales	(2,655)	(2,529)	(8,526)	(7,272)
Settlements	0	0	0	0
Transfers into Level 3	37	206	37	206
Transfers out of Level 3	(95)	(38)	(53)	(129)
Balance at end of period	1,094	1,164	1,094	1,164
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	106	153	140	243
Total increase (decrease) in unrealized gains included in cost of products sold	54	76	194	171
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	(82)	(85)	(291)	(302)
Transfers into Level 3	45	66	111	132
Transfers out of Level 3	(3)	(6)	(34)	(40)
Balance at end of period	$ 120	$ 204	$ 120	$ 204