Fair Value Measurements (Reconciliation Of Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 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)	$ (118)	$ (79)	$ (364)	$ (204)
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	222	186	142	172
Total increase (decrease) in unrealized losses included in cost of products sold	118	73	372	197
Purchases	30	2	54	19
Sales	(12)	(5)	(61)	(25)
Settlements	(130)	(123)	(348)	(289)
Transfers into Level 3	30	35	136	108
Transfers out of Level 3	(11)	(3)	(48)	(17)
Balance at end of period	247	165	247	165
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	22	32	39	30
Total increase (decrease) in unrealized losses included in cost of products sold	4	(9)	12	(4)
Purchases	30	2	54	19
Sales	(12)	(5)	(61)	(25)
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	44	20	44	20
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	200	154	103	142
Total increase (decrease) in unrealized losses included in cost of products sold	114	82	360	201
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	(130)	(123)	(348)	(289)
Transfers into Level 3	30	35	136	108
Transfers out of Level 3	(11)	(3)	(48)	(17)
Balance at end of period	$ 203	$ 145	$ 203	$ 145