Fair Value Measurements (Reconciliation Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 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)	$ 182	$ 18
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	1,462	1,247
Total increase (decrease) in unrealized gains included in cost of products sold	(159)	(51)
Purchases	3,248	2,356
Sales	(3,194)	(2,237)
Settlements	(69)	(97)
Transfers into Level 3	81	120
Transfers out of Level 3	(67)	(151)
Balance at end of period	1,302	1,187
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	1,322	1,004
Total increase (decrease) in unrealized gains included in cost of products sold	(228)	(114)
Purchases	3,248	2,356
Sales	(3,194)	(2,237)
Settlements	0	0
Transfers into Level 3	34	88
Transfers out of Level 3	(53)	(128)
Balance at end of period	1,129	969
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	140	243
Total increase (decrease) in unrealized gains included in cost of products sold	69	63
Purchases	0	0
Sales	0	0
Settlements	(69)	(97)
Transfers into Level 3	47	32
Transfers out of Level 3	(14)	(23)
Balance at end of period	$ 173	$ 218