Fair Value Measurements (Narrative) (Details) - Significant Unobservable Inputs (Level 3) [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Fair Value Measurements [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 669	$ 106
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 532	$ 260
Assets [Member] \| Weighted Average [Member] \| Fair Value, Measurements, Recurring [Member] \| Inventories Component [Member]
Fair Value Measurements [Line Items]
Basis	18.50%	12.80%
Liabilities [Member] \| Weighted Average [Member] \| Fair Value, Measurements, Recurring [Member] \| Inventories Component [Member]
Fair Value Measurements [Line Items]
Basis	125.00%	99.90%

Adjustment to current market value, based on location, that a market participant is willing to pay, used as an input to measure fair value.

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- Definition

Fair Value Measurements [Line Items]

+ References

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- Definition

Amount of unrealized (holding) gain (loss) which is included in the statement of income (or changes in net assets) related to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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Amount of unrealized (holding) gain (loss) which is included in the statement of income (or changes in net assets) related to those liabilities still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

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