Fair Value Measurements (Fair Value Measurements At Reporting Date) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets:
Marketable securities	$ 92	$ 483
Deferred receivables consideration	307	540
Fair Value, Measurements, Recurring [Member]
Assets:
Inventories carried at market	4,886	4,424
Cash Equivalents	352	286
Marketable securities	92	477
Segregated investments	1,733	1,613
Deferred receivables consideration	307	540
Total Assets	7,819	7,964
Liabilities:
Inventory-related payables	719	521
Total Liabilities	1,183	1,172
Fair Value, Measurements, Recurring [Member] | Commodity Contracts [Member]
Assets:
Derivative Asset	386	511
Liabilities:
Derivative Liability	371	561
Fair Value, Measurements, Recurring [Member] | Foreign Exchange Contracts [Member]
Assets:
Derivative Asset	63	102
Liabilities:
Derivative Liability	92	90
Fair Value, Measurements, Recurring [Member] | Interest Rate Contracts [Member]
Assets:
Derivative Asset		11
Liabilities:
Derivative Liability	1
Fair Value, Measurements, Recurring [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Assets:
Inventories carried at market	0	0
Cash Equivalents	352	286
Marketable securities	91	408
Segregated investments	1,733	1,613
Deferred receivables consideration	0	0
Total Assets	2,176	2,307
Liabilities:
Inventory-related payables	0	0
Total Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Commodity Contracts [Member]
Assets:
Derivative Asset	0	0
Liabilities:
Derivative Liability	0	0
Fair Value, Measurements, Recurring [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Foreign Exchange Contracts [Member]
Assets:
Derivative Asset	0	0
Liabilities:
Derivative Liability	0	0
Fair Value, Measurements, Recurring [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Interest Rate Contracts [Member]
Liabilities:
Derivative Liability	0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Inventories carried at market	3,400	3,102
Marketable securities	1	69
Deferred receivables consideration	307	540
Total Assets	4,046	4,195
Liabilities:
Inventory-related payables	680	491
Total Liabilities	1,041	1,000
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Commodity Contracts [Member]
Assets:
Derivative Asset	275	371
Liabilities:
Derivative Liability	268	419
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Foreign Exchange Contracts [Member]
Assets:
Derivative Asset	63	102
Liabilities:
Derivative Liability	92	90
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Contracts [Member]
Assets:
Derivative Asset		11
Liabilities:
Derivative Liability	1
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Inventories carried at market	1,486	1,322
Marketable securities	0	0
Deferred receivables consideration	0	0
Total Assets	1,597	1,462
Liabilities:
Inventory-related payables	39	30
Total Liabilities	142	172
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Commodity Contracts [Member]
Assets:
Derivative Asset	111	140
Liabilities:
Derivative Liability	103	142
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Foreign Exchange Contracts [Member]
Assets:
Derivative Asset	0	0
Liabilities:
Derivative Liability	0	$ 0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Interest Rate Contracts [Member]
Liabilities:
Derivative Liability	$ 0