Fair Value Measurements (Reconciliation Of Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$ 172	$ 129
Total increase (decrease) in unrealized gains included in cost of products sold	253	579
Purchases	38	16
Sales	(25)	(15)
Settlements	(397)	(476)
Transfers into Level 3	128	158
Transfers out of Level 3	(27)	(219)
Balance at end of period	142	172
Commodity Derivative Contracts Losses [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	142	113
Total increase (decrease) in unrealized gains included in cost of products sold	257	566
Purchases	0	0
Sales	0	0
Settlements	(397)	(476)
Transfers into Level 3	128	158
Transfers out of Level 3	(27)	(219)
Balance at end of period	103	142
Inventory Related Payables [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	30	16
Total increase (decrease) in unrealized gains included in cost of products sold	(4)	13
Purchases	38	16
Sales	(25)	(15)
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance at end of period	$ 39	$ 30