Fair Value Measurements (Reconciliation Of Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ (48)	$ 85	$ (246)	$ 124
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	366	151	142	172
Total increase (decrease) in unrealized losses included in cost of products sold	39	72	254	124
Purchases	3	16	24	17
Sales	(47)	(3)	(49)	(20)
Settlements	(161)	(98)	(218)	(166)
Transfers into Level 3	41	49	106	73
Transfers out of Level 3	(19)	(1)	(37)	(14)
Balance at end of period	222	186	222	186
Significant Unobservable Inputs (Level 3) [Member] | Inventory Related Payables [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	75	28	39	30
Total increase (decrease) in unrealized losses included in cost of products sold	(9)	(9)	8	5
Purchases	3	16	24	17
Sales	(47)	(3)	(49)	(20)
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance at end of period	22	32	22	32
Significant Unobservable Inputs (Level 3) [Member] | Commodity Derivative Contracts Losses [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	291	123	103	142
Total increase (decrease) in unrealized losses included in cost of products sold	48	81	246	119
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	(161)	(98)	(218)	(166)
Transfers into Level 3	41	49	106	73
Transfers out of Level 3	(19)	(1)	(37)	(14)
Balance at end of period	$ 200	$ 154	$ 200	$ 154