Derivative Instruments and Fair Value Measurements - Narrative (Details) $ in Millions	9 Months Ended
Sep. 30, 2017 USD ($)
Derivative [Line Items]
Net deferred losses reported in AOCI to be reclassified into income in the next twelve months	$ (8)
Fair value of derivative instruments with credit-risk-related contingent features in a liability position	55
Additional collateral required to be posted if the credit risk related contingent features were triggered	48
Collateral posted	0
Accounts Receivable, Net
Derivative [Line Items]
Collateral posted	7
Accounts Receivable, Net \| Exchange-traded commodity
Derivative [Line Items]
Margin deposits	$ 9
Five Largest Accounts \| Customer Concentration Risk \| Accounts Receivable, Net
Derivative [Line Items]
Concentration percentage	28.00%

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624258-113959

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The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 1
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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
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Fair value of credit risk derivative liability.

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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.

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The amount of cash or securities placed with a broker or counterparty as security for a trading or derivatives securities position which was partially obtained with funds provided by the broker dealer.

+ References

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-Publisher FASB
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