Fair Value Measurements (Reconciliation Of Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$ 226	$ 263
Total increase (decrease) in unrealized gains included in cost of products sold	1,746	397
Purchases	37	48
Sales	(36)	(38)
Settlements	(1,059)	(451)
Transfers into Level 3	112	51
Transfers out of Level 3	(63)	(44)
Balance at end of period	963	226
Commodity Derivative Contracts Losses [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	199	245
Total increase (decrease) in unrealized gains included in cost of products sold	1,729	398
Purchases	0	0
Sales	0	0
Settlements	(1,059)	(451)
Transfers into Level 3	112	51
Transfers out of Level 3	(63)	(44)
Balance at end of period	918	199
Inventory Related Payables [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	27	18
Total increase (decrease) in unrealized gains included in cost of products sold	0	(1)
Purchases	20	48
Sales	(36)	(38)
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance at end of period	11	27
Long-term Debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	0
Sales	0
Settlements	0
Transfers into Level 3	0
Transfers out of Level 3	$ 0
Balance at end of period		$ 0