Accounting for Derivative Instruments and Hedging Activities - Pre-tax effects of economic hedges not designated a cash flow hedges (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Unrealized mark-to-market results
Reversal of previously recognized unrealized losses on settled positions related to economic hedges	$ 2	$ 3
Net unrealized gains/(losses) on open positions related to economic hedges	194	(22)
Total unrealized mark-to-market gains/(losses) for economic hedging activities	196	(19)
Reversal of previously recognized unrealized gains on settled positions related to trading activity	(3)	(15)
Net unrealized gains on open positions related to trading activity	11	1
Total unrealized mark-to-market gains/(losses) for trading activity	8	(14)
Total unrealized losses	204	(33)
Credit Risk Related Contingent Features
Unrealized gain (loss) from open economic hedge positions	194	(22)
Collateral due on net liability position that has not been called by a certain marginable agreement counterparty	5
Adequate Assurance Clauses
Credit Risk Related Contingent Features
Derivative net liability position, collateral required Contracts with Credit Rating Contingent Feature	20
Credit Rating Contingent Features
Credit Risk Related Contingent Features
Derivative net liability position, collateral required Contracts with Credit Rating Contingent Feature	5
Commodity contracts
Unrealized mark-to-market results
Total unrealized losses	204	(33)
Commodity contracts \| Sales
Unrealized mark-to-market results
Total unrealized losses	(98)	104
Commodity contracts \| Cost of Sales
Unrealized mark-to-market results
Total unrealized losses	302	(137)
Interest rate contracts
Unrealized mark-to-market results
Total unrealized losses	$ 48	$ 5

-- None. No documentation exists for this element. --

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This element represents the amount recorded in the entity's statement of operations for net unrealized gains (losses) on open positions related to trading activities.

+ References

No definition available.

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Amount reversed into entity's statement of operations for previously recognized unrealized (gains) losses on settled positions related to economic hedges.

+ References

No definition available.

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- Definition

Amount reversed into entity's statement of operations for previously recognized unrealized (gains) losses on settled positions related to trading activities.

+ References

No definition available.

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- Definition

Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities

+ References

No definition available.

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Unrealized Gain (Loss) on Derivatives, Mark To Market, Trading Activities

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No definition available.

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- Definition

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
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

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- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

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- Definition

Amount of unrealized gain (loss) related to derivatives designated as cash flow hedging instruments, recorded in results of operations to the extent that the cash flow hedge is determined to be ineffective.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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