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Fair Value Measurements - Recurring - Changes in Level 3 Measurements (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017
Commodity Derivative Contracts (net) |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |
Fair value at beginning of period |  | $ (2) | $ (6)
Total gains (losses) (realized and unrealized) included in earnings | [1] | 0 | 5
Settlements |  | 0 | 1
Fair value at end of period |  | (2) | 0
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized losses relating to liabilities still held at end of period |  | 0 | 5
Embedded Derivatives in Commodity Contracts (net) |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |
Fair value at beginning of period |  | (64) | (54)
Total gains (losses) (realized and unrealized) included in earnings | [1] | 3 | 8
Settlements |  | 3 | 2
Fair value at end of period |  | (58) | (44)
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized losses relating to liabilities still held at end of period |  | $ 3 | $ 8
[1] | (1)Gains and losses on Commodity Derivative Contracts classified as Level 3 are recorded in “Product sales” in the accompanying Consolidated Statements of Income. Gains and losses derivatives embedded in commodity contracts are recorded in “Purchased product costs” and “Cost of revenues.”

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- Definition This element represents total unrealized gains or losses for the period, arising from assets and liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings. Such unrealized gains or losses relate to those contracts still held at the reporting date. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Amount of gain (loss) recognized in the income statement of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19279-110258 + Details
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- Definition Amount of settlements of financial instrument classified as a derivative asset (liability) after deduction of derivative liability, measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19279-110258 + Details
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- Definition Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19279-110258 + Details
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