Fair Value Measurements (Reconciliation Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
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	219	236
Purchases	11,236	9,900
Sales	(11,231)	(9,567)
Settlements	(369)	(420)
Transfers into Level 3	377	238
Transfers out of Level 3	(97)	(172)
Balance at end of period	1,597	1,462
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	(29)	44
Purchases	11,236	9,900
Sales	(11,231)	(9,567)
Transfers into Level 3	241	70
Transfers out of Level 3	(53)	(129)
Balance at end of period	1,486	1,322
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	248	192
Settlements	(369)	(420)
Transfers into Level 3	136	168
Transfers out of Level 3	(44)	(43)
Balance at end of period	$ 111	$ 140